Preparing for floods: interim guidance for improving the ... · ODPM Publications Centre PO Box 236 Wetherby West Yorkshire LS23 7NB Tel: 0870 1226 236 Fax: 0870 1226 237 Textphone:

Preparing for

Interim guidance for improving the flood resistance ofdomestic and small business properties

October 2003

FLOODS

Photo AcknowledgmentsEnvironment Agency, Kyriacos Akathiotis,Solent News Agency, HR Wallingford,WS Atkins, Lucy and Anthony Rees.

Office of the Deputy Prime MinisterEland HouseBressenden PlaceLondon SW1E 5DUTelephone 020 7944 4400Internet service www.odpm.gov.uk

© Crown copyright 2002.

Reprinted with amendments 2003Copyright in the typographical arrangement anddesign rests with the Crown.

This publication (excluding the Royal Arms andlogos) may be reproduced free of charge in anyformat or medium provided that it is reproducedaccurately and not used in a misleading context.The material must be acknowledged as Crowncopyright with the title and source of thepublication specified.

Further copies of this report are available from:

ODPM Publications CentrePO Box 236WetherbyWest YorkshireLS23 7NBTel: 0870 1226 236Fax: 0870 1226 237Textphone: 0870 1207 405E-mail: [email protected]

This document is also available on the ODPMwebsite: www.odpm.gov.uk

Published by the Office of the Deputy PrimeMinister. Amended and reprinted in the UK,October 2002 on material containing 75% post-consumer waste and 25% ECF pulp.

Product code 01CD1025

Contents

Foreword 1

Acknowledgments 3

1. Introduction 5

2. The Impact of Flooding 11The causes of flooding 11Flood damage – the effects of flooding 16

3. Existing Property Owners 25Assessing the risk of flooding 25Choosing the right options 36Keeping the water out using flood barriers 40Other permanent measures to improve flood 46resistance of propertyHistoric buildings 47

4. New Development 51Introduction 51Planning Guidance 51General principles of flood resistant design for 52new developmentInterface with Building Regulations 54

5. Permanent Measures to Reduce Flood 55Damage – New and Existing PropertiesIntroduction 55External walls 56Internal walls 62Floors 65Fittings and building services 72

6. Summary 83

7. Further Reading 87

8. Environment Agency Guidance 91

GENERAL

GENERAL

EXISTING PROPERTY OWNERS

DEVELOPERS

BUILDERS &EXISTING PROPERTY OWNERS

GENERAL

GENERAL

GENERAL

Preparing for Floods

Foreword

Foreword

I am pleased to welcome this interim guidance“Preparing for Floods”.

Recent occurrences of flooding in the UK have shownthe devastating effects that these events can have onpeople’s homes and businesses. Following the floodsduring the autumn of 2000, the Parliamentary SelectCommittee for the Environment, Transport andRegional Affairs recommended that guidance beproduced containing information for use by planningauthorities and advice on ways to improve theresistance to flooding of existing properties. Thisdocument has been produced in response to thoserecommendations.

The information compiled in this documentcomplements existing planning guidance and alsoadvice on taking extemporary measures to protectagainst flooding, which is available through theEnvironment Agency. The production of this interimguidance has been overseen by the UK’s leadingresearch and technical experts on flooding,organisations representing construction and insurancecompanies, the Environment Agency and twoGovernment Departments. It contains informedadvice that is relevant to the owners of homes andsmall businesses and people undertaking buildingwork as well as planning authorities.

This guidance has been produced quickly, so as tobring together information which will be of practicalhelp to those at immediate risk of flooding. We havenot been able to consult as widely as we would havewished with potential users on the content of thedocument, so any comments on the guidance, andhow it can be improved, would be welcomed. Furtherresearch into improving the flood resistance ofbuildings is being undertaken and we will update theguidance in the light of the research and anycomments received.

1

Since the impacts of

flooding are so devastating,

it is important that people

whose properties are at risk

take appropriate action to

resist flooding. Much can be

done to reduce the damage

caused by floods as this

guidance shows. We hope it

will be of practical help to

all those whose homes or

businesses may be at risk.


As well as the damage caused to property, floodinghas many other, less tangible, impacts on people’slives. These include the loss of sentimentalbelongings, the nuisance of cleaning up following a flood, inconvenience of having to live in temporaryaccommodation while this clean up takes place, andconcerns over security of empty properties.

Since the impacts of flooding are so devastating, it isimportant that people whose properties are at risktake appropriate action to resist flooding. Much canbe done to reduce the damage caused by floods asthis guidance shows. We hope it will be of practicalhelp to all those whose homes or businesses may beat risk.

2

Sally Keeble

Acknowledgments

Acknowledgments

Funding contributions for the project were provided by:The former Department for Transport, LocalGovernment and the RegionsDepartment of Trade and IndustryScottish ExecutiveEnvironment AgencyAssociation of British InsurersNHBC (National House Building Council)House Builders Federation.

The project steering group, who assisted with thedevelopment of the guidance, was managed by theConstruction Industry Directorate of the Departmentof Trade and Industry.

The project steering group consisted ofrepresentatives from the followingorganisations:

The former Department for Transport, LocalGovernment and the RegionsDepartment of Trade and IndustryScottish ExecutiveWelsh Assembly Government Environment AgencyAssociation of British Insurers (ABI)NHBC (National House Building Council)House Builders Federation (HBF)Building Research Establishment (BRE)Construction Industry Research and InformationAssociation (CIRIA)HR Wallingford.

The project steering group have contributedmuch of the technical information containedwithin this guide. The guidance thereforerepresents the industry’s current consensus viewon improving flood resistance of domesticproperties.

3


This document was updated with minor revisions(e.g. organisations; details of current projects, etc) inOctober 2003. Consideration will be given toproduction of a new edition following the completionby CIRIA in 2004 of its collaborative R&D project on‘Standards for the repair of buildings followingflooding’.

The guide was prepared by the research contractor,WS Atkins Consultants Ltd.

Please send any comments on the usefulness ofthis guidance, and how it can be improved, to:Buildings Division, ODPM, Eland House, Bressenden Place, London, SW1E 5DU (Fax: 020 7944 5739 or 5719; E-mail: [email protected]).

4

Introduction

Recent flooding events across the UK have shown thedevastating impact that flooding can have onpeople’s lives and businesses. During the autumn2000 floods alone over 10,000 homes and businesseswere flooded, causing damage to property andsevere distress to thousands of people across thecountry.

While it is not possible to eliminate the risk offlooding altogether, many practical steps can betaken to reduce the cost of flood damage repairs andspeed up recovery times. Although existing river andflood defences protect extensive areas of the UK,they cannot be designed to protect against extremeflooding events. Flood defences can only beimplemented in areas where the potential benefitsoutweigh the financial costs.

The aim of this guide is to provide guidance toproperty owners on how they can improve the floodresistance of their properties. The guide is alsointended for use by developers, local planningauthorities and others involved in construction ofnew buildings, and renovation of existing buildings,at risk of flooding. If adopted, the principles set outwithin this guide should help reduce the stress anddisruption of flooding and provide a more sustainableapproach to flood risk.

In preparing this guide, information has been drawnfrom Government, the Environment Agency, theInsurance industry, local authorities and, mostimportantly, families and small businesses who havebeen through the experience of a major flood. This isthe first time that best available information onimproving the flood resistance of buildings has beencollated within one document. The guide does notattempt to solve all the problems associated with

5

Introduction1

If adopted, the principles set

out within this guide should

help reduce the stress and

disruption of flooding and

provide a more sustainable

approach to flood risk.


flood damage but it does provide a range ofcommon-sense solutions and references to othersources of information.

The guide has been published as “Interim Guidance”and will be reviewed and updated in due course asadditional information is obtained. This document hasbeen prepared in response to a recommendationmade by the Parliamentary Select Committee for theEnvironment, Transport and Regional Affairsfollowing the autumn 2000 floods, to providesupplementary planning guidance for use by planningauthorities and information on improving floodresistance of existing properties.

Before undertaking any works referred towithin this guide it is important thatprofessional advice is first obtained to ensurethat the most appropriate improvementmeasures are chosen for the propertyconcerned.

What can I expect to find out in this guide?

This guide provides practical information on themeasures that can be taken to improve the floodresistance of both existing and new properties at riskof flooding within the UK. The guide is aimed at thefollowing target audiences:

• Existing homeowners and small business ownerswhose properties are at risk of flooding.

• Developers, builders, local planning authorities,building control bodies (local authority buildingcontrol or private approved inspectors) and othersinvolved with:

– Construction of new properties in areas of floodrisk; and

– Renovation of existing buildings in areas of flood risk.

Sections 1 and 2 provide a general introduction andsome background information on the causes andimpact of flooding.

6

This document has been

prepared in response to a

recommendation made by

the Parliamentary Select

Committee for the

Environment, Transport and

Regional Affairs following

the autumn 2000 floods, to

provide supplementary

planning guidance.

Introduction

Section 3 is aimed principally at existing homeownersand small business owners. It provides information onassessing the risks of flooding and guidance onselecting appropriate measures to improve the floodresistance of properties. Information is also providedon measures to prevent or reduce the volume offloodwater entering the building, including the use oftemporary flood barriers and other permanentmeasures to improve the flood resistance of thebuilding structure.

Many areas prone to flooding are in historic townsand villages, and contain properties of specialarchitectural or historic interest. Section 3 providesoutline advice on the special considerations thatapply to these buildings and gives references to moredetailed guidance provided by English Heritage.

Section 4 of this guide is for use by developers, localauthorities, building control bodies and othersinvolved with new development in high flood riskareas. It provides guidance on the forms ofconstruction that are most appropriate fordevelopments at risk of flooding.

New development in areas at risk of flooding is nowonly permitted in exceptional cases in accordancewith the Government’s new planning guidance ondevelopment and flood risk (Planning and PolicyGuidance Note 25: Development and Flood Risk(PPG25)). The guidance within PPG25 is based on aprecautionary approach so that risk is avoided wherepossible and managed elsewhere. The relevantdocument in Scotland is National Planning PolicyGuideline NPPG7 – Planning and Flooding. In Walesnew policy on development and flood risk isemerging through Draft Planning Policy Wales (PPW)and the revision of Technical Advice Note 15Development and Flood Risk (TAN 15).

Section 5 provides more technical information on thepermanent measures that can be taken to improvethe flood resistance of both existing and newbuildings with sub-sections discussing walls, floors

7

Many areas prone to

flooding are in historic

towns and villages, and

contain properties of special

architectural or historic

interest.


and building services and fittings (such as electricalwiring and fitted cupboards ). This section is aimedprincipally at builders but may also be of interest toproperty owners.

Section 6 provides a summary of the key steps toreducing the consequences of flooding as outlinedwithin the guide. Section 7 includes a list of relatedpublications for further reading, and Section 8 givesguidance from the Environment Agency’s Floodlineservice.

Case studies are included throughout this guide togive real-life examples of what steps homeownersand small business owners have taken to protect theirproperties from flooding. The first case studydescribes the measures taken by a fish and chip shopowner in the town of Bewdley, Worcestershire.Bewdley was severely affected by the autumn 2000floods when the River Severn overtopped its banks.

In addition to this guide there are many other on-going initiatives to improve flood protection of homesand businesses, including the planning, design andconstruction of flood defence improvements by theEnvironment Agency and local authorities, andimprovements to sewers by water companies. Otherflood related research projects are also underwayincluding work to provide national performancestandards against which flood protection productscan be tested, and work to improve knowledge onthe flood resistance of building materials.

It should be noted that while this guide providesinformation on how to improve flood resistance ofproperties it does not cover the steps required to clean,dry and restore properties after flooding has occurred.Information related to this is provided by CIRIA and theEnvironment Agency in their leaflets ‘After a Flood’ and‘Flood Products’. Further information is provided on theCIRIA website (www.ciria.org/flooding) where a seriesof advice sheets aimed at the householder on how toimprove the overall flood resistance of their homecan be found together with other pages on repairand restoration of buildings following floods.

8

In addition to this guide

there are many other on-

going initiatives to improve

flood protection of homes

and businesses, including

the planning, design and

construction of flood

defence improvements by

the Environment Agency

and local authorities.

Introduction

The Merchant’s Fish Bar occupies a prime site inBewdley, standing at the end of the main street, closeto the river, next to a pub. It is used by local residentsall year round, and by day-trippers, steam trainenthusiasts, holidaymakers and fishermen throughthe summer. The popularity of Bewdley as a touristtown gives the shop one of the best turnovers for itssize in the Midlands.

The chip shop and the tearoom next door belong toKyriacos Akathiotis, who has owned the business forthe last 17 years. In November 2000, the river rose tothe windowsills of the tearoom, flooding the riversidehouses, the chip shop, the pub forecourt and shopsfurther up the street. Kyriacos suffered an uninsuredloss of around £175,000. His insurance policyexcluded flood cover.

All the equipment in the chip shop had to be strippedout. There was no way of saving the fryers andfridges from that depth of water. Not only was therethe actual physical damage, but in a businesssupplying food, cleansing after a flood has to meetstringent standards of hygiene. “Everything went inthe bin, everything.” Much less damage was done inthe tearoom, where the equipment and furniture wassmaller and could be carried to safety.

He says he cannot afford for this to happen againand in the £100,000 refit following the flooding, hehas adapted the shop and the equipment to takeaccount of the possible risks.

The new fryers, which normally would have costaround £21,000, have been set on a hydraulic systemwhich enables them to be raised above the floodlevel – this at an extra cost of £14,000. The ductingfor the ventilation system has also been sealed toprevent water ingress. Before this work was carriedout, water entering the ducting used to stop theventilation from working and the shop had to close.The seven or eight fridges that the shop needs arenow all made from stainless steel, with the motorsset at the top rather than the bottom. Apart from the

9

CaseStudyCS


fryers, all the other equipment can now be removedbefore flooding occurs.

These remedial works will substantially reduce anyfuture flood damage repair costs and will allow thepremises to re-open for business more quickly ifflooding returns.

Source: Kyriacos Akathiotis

10

The Impact of Flooding

The causes of flooding

Flooding generally occurs through a combination ofevents:

• Rainfall fills rivers, streams and ditches beyond theirflow capacity. Floodwater overflows river banks andflood defences onto floodplains.

• Coastal storms can lead to overtopping andbreaching of coastal flood defences due to stormsurge and wave action.

• Blocked or overloaded drainage ditches, drains andsewers overflow across roads, gardens and intoproperty.

• Overloaded sewers can sometimes backflow intoproperty.

• Rain can be so heavy that run-off flows overlanddown hills and slopes.

• Rain soaks into the ground causing ground waterlevels to rise and flood.

Flooding in autumn 2000 was caused by a series ofstorms which crossed the country over a seven-weekperiod. Areas soon became waterlogged, resulting inrivers and streams rising very quickly as more rain fell.Many of the rainfall storms would have been severeenough to cause flooding on their own, but thecombination of storms led to repeated flooding inmany places and to prolonged flooding in others.

11

The Impact of Flooding2


In November 2000, the equivalent of two month’srain fell on the Yorkshire Dales in 10 days. It wasthe wettest autumn for 100 years resulting in thehighest recorded water levels for many riversdownstream. Fresh rain produced new torrents ofwater flowing into rivers that were alreadydangerously swollen. The resulting floods causedhavoc in Yorkshire and other regions. Along riverbanks in many parts of Britain water poured intohouses, sometimes whole estates. Months latermany victims were still not able to move back intotheir homes (BBC, Panorama 2001).

Flooding is not new

Flooding is not new to the UK and there are accountsof flooding causing severe damage and loss of lifesince records began.

“The central arch of Wallingford Bridge was sweptaway. Water reached as high as parlour windows andmany poor people ‘lost their all’. At Windsor, theEton Bridge was carried away and the fifteenth archof the Eton to Slough Bridge capsized due to theviolence of the surging waters. The people of Bishamalso lost their Green Bridge and there was nochurching on the following Sunday as the water wasso high”. The Great Thames flood of 1809 (Currieet.al, 1994).

“The 1894 floods were so spectacular, socatastrophic and so widespread that they were totake place in Berkshire’s folklore as the greatestfloods ever and the yardstick by which all futureinundations in the county would be measured. TheThames burst its banks and invaded scores of towns,villages, hamlets and farmsteads, thousands wereaffected”. (Currie et.al, 1994).

Despite the long history of flooding in the UK,experience in recent years suggests that the situationis getting worse. Changes in land and rivermanagement, development in floodplains and floodrisk areas, and variations in the intensity of rainfall

12

“The 1894 floods were so

spectacular, so catastrophic

and so widespread that they

were to take place in

Berkshire’s folklore as the

greatest floods ever and the

yardstick by which all future

inundations in the county

would be measured.”


may have all contributed to the severity of floodevents and their impacts.

There is also growing evidence that our climate ischanging because of pollution and that this changingclimate will increase the likelihood of flooding. This isdue to predicted increases in sea levels and increasesin the duration and intensity of rainfall, especially inwinter months. It is therefore likely that river, coastaland other types of flooding will affect more areas ofthe country with greater severity in future years.Over the last few years we have certainly seen worsethan average weather conditions.

What are the risks of flooding?

It has been estimated that over 5% of the people inEngland live lower than 5 metres above sea level,including large parts of our major cities such as Yorkand London. It has also been suggested that about7% of the country is likely to flood at least onceevery 100 years from rivers. In addition,approximately 30% of the coastline is developed andaround 1.5% of the country is at risk from directflooding from the sea. As a result, about 1.7millionhomes and 130,000 commercial properties worthover £200 billion, are at risk from river or coastalflooding in England. Many more properties are at riskfrom localised flash flooding.

Weather claims (including those for storm damage,burst pipes and flooding) form just part of theoverall claims picture for insurance companies.Nevertheless the insurance industry takes flood riskvery seriously. In the autumn 2000 event over10,000 homes were flooded resulting in over200,000 insurance claims. The current costestimate for the autumn 2000 floods is over £800million (Association of British Insurers).

13


What are the sources of flooding?

There are a number of different sources of floodingincluding:

• Rivers and streams

• The sea

• Groundwater

• Overland flow (especially over tarmac and otherhard surfaces)

• Blocked or overloaded drains and sewers

• Broken water mains.

• Rivers and streams. Excessive rainfall, snow orhail, or a combination of high river levels and hightides can cause river flooding. Flooding occurswhen surface water run-off from the surroundingarea exceeds the flow capacity of the river orstream. Saturation of surface soils due to wetweather can lead to greater run-off rates andhigher flooding levels.

Human activity has increased the risk of floodingfrom rivers and streams in many areas.Development has reduced the natural capacity offloodplains and increased the rate of surface waterrun-off.

Most areas are protected against river flooding byman-made flood defences. While these defencesreduce the likelihood of flooding they cannoteliminate risk altogether. Defences are designed towithstand specific flood heights but they can bebreached or overtopped should more extremeevents occur.

• The sea. Flooding from the sea can be caused byhigh tides, storm surges, waves overtopping orbreaching sea defences, or a combination of thesefactors.

• Groundwater flooding. Flooding fromgroundwater is most likely to occur in areas ofchalk, limestone or other aquifers. This type offlooding generally affects older buildings that backonto hillsides, buildings close to winterbournestreams or houses with basements that are

14


particularly prone to groundwater flooding.Depending on the local geology, groundwaterflooding can take a long time to recede. Propertiescan still be underwater many months after theheavy rains that caused the flooding have passed.

The heavy rainfall in autumn 2000 followed thewettest 12 months on record in many areas ofEngland and Wales. These high volumes of rainfallled to many aquifers recharging earlier than normal,leading to unusually high levels of groundwater. Insome areas, groundwater rose to the surface andformed springs, often in places where springs hadnot been seen for a generation or more. As a resultapproximately 1,000 homes and businesses wereaffected by groundwater flooding.

• Flooding from overland flow. Overland flows canbe caused by heavy rainfall falling on saturatedground, where groundwater levels are already high,or on paved areas of tarmac or concrete withinadequate drainage. Properties can be flooded byoverland flows if they are located in areas wherefloodwater can accumulate. Paved areas, such asroads, can act as channels for overland flows.

• Blocked or overloaded drainage systems.Localised flash flooding from blocked or overloadeddrainage systems can occur at times of heavyrainfall. This type of flooding is unpredictable andoften occurs in unexpected locations depending onthe location and intensity of rainfall.

Such drainage systems include open drainageditches & culverts and buried drains and sewers.Where flooding occurs from foul sewers the floodwaterwill often be contaminated with sewage. In somecases, contaminated floodwater can flow backthough foul sewers causing flooding inside buildings.

Flooding can also be caused by blocked oroverloaded roof drainage systems.

• Broken water mains. Localised flooding can becaused by burst water mains, although this rarelyleads to property flooding above ground level.Basements can be flooded if a water main burstsclose by.

15


Why do properties flood?

The extent to which flooding affects individualproperties will depend on the speed and depth of thefloodwater and the particular level and position ofthe building. The adjacent chart shows thedistribution of flooded properties by flood type,based on information collated from the autumn 2000floods.

Flood damage – the effects offlooding Flood damage can range from being relatively minor,where very limited volumes of floodwater enter thebuilding, to severe cases of deep water floodingwhere extensive damage occurs to the building andits contents. The amount of damage depends mainlyon the depth and duration of flooding.

The most important aspect to remember is that thedamage to property is only a small element of thetrue ‘human cost’ of a flood. The stress associatedwith losing personal belongings, having to live intemporary accommodation while repairs areundertaken, and the trauma of the clean-up andrestoration can be considerable. There are manyfactors that contribute to the suffering of individualsaffected by flooding. These can include:

• The loss of personal belongings, particularly thoseof sentimental value that cannot be replaced.

• The financial pressures of repairing flood damage,particularly for people who are not fully insured.

• Cleaning the property following flooding. Residual smells.

• Arranging repair work.

• The loss of employment or a business failure.

• The additional costs and stress of having to live intemporary accommodation while the property isrenovated. Worries over the security of the emptyproperty.

• The loss of pets.

16

28%

40%

18%

14%

Autumn 2000 floods: causes ofproperty flooding

Adapted from the EnvironmentAgency’s Lessons Learned Report

Overtopping of river defence

No flood protection on river

Flooding from streams andditches

Inadequate drainage etc.


• Damage to garages, garden plants/ponds, shedsand outbuildings.

• Potential reduction in property value.

• The fear of flooding happening again.

Flood depth

The water depth is clearly the key factor affecting thescale of flood damage. For very shallow flooding,where water does not rise above floor level, damageis unlikely to be significant for most properties.However, it should be remembered that even inshallow cases of flooding water can enter cellars,basements and voids beneath floors, and can causeproblems of damp in walls.

Damage increases significantly once water rises abovethe floor level and comes into contact with internalsurfaces, electrical sockets and equipment, kitchencupboards, carpets, furniture, and personalbelongings. Flood depths greater than 1 metre abovefloor level are likely to result in structural damage ofbuildings. The table on page 18 illustrates the typicalincrease in flood damage as the depth of floodwaterrises.

Research by the insurance industry has shown thathalf a metre of floodwater within a modernsemidetached house will result in an average cost of£15,000 to repair the building and around £9,000 toreplace damaged belongings (Information providedby the Association of British Insurers).

17

Damage increases

significantly once water rises

above the floor level and

comes into contact with

internal surfaces, electrical

sockets and equipment,

kitchen cupboards, carpets,

furniture, and personal

belongings.

Preparin

g fo

r Floo

ds

18

Depth of floodwater Damage to the building Damage to services and Damage to personalfittings possessions

Below ground floor level.

Up to half a metre aboveground floor level.

More than half a metreabove ground floor level.

Minimal damage to the mainbuilding.

Floodwater may enterbasements, cellars and voidsunder floors.

Possible erosion beneathfoundations.

Damage to internal finishes,such as wall coverings andplaster linings. Wall coveringsand linings may need to bestripped to allow walls to dry.

Floors and walls will becomesaturated and will requirecleaning and drying out.Damp problems may result.

Chipboard flooring likely torequire replacement.

Damage to internal andexternal doors and skirtingboards.

Increased damage to walls.Possible structural damage.

Damage to electrical socketsand other services inbasements and cellars.

Carpets in basements andcellars may need to bereplaced.

Damage to downstairselectricity meter andconsumer unit (fuse box).

Damage to gas meters andlow-level boilers andtelephone services.

Carpets and floor coveringsmay need to be replaced.

Chipboard kitchen units arelikely to require replacement.

Washing machines, freestanding cookers, fridges andfreezers may need to bereplaced.

Damage to higher units,electrical services andappliances.

Possessions and furniture inbasements and cellarsdamaged.

Damage to sofas, otherfurniture, and electricalgoods.

Damage to small personalpossessions, such as books,audio cassettes, videos, andphotos.

Food in lower kitchencupboards may becontaminated.

Damage to possessions onhigher shelves.

Floo

d d

amag

e for a typ

ical residen

tial pro

perty


Flooding duration

The length of time that floodwater remains in contactwith buildings is another key factor in the level ofdamage caused. Generally the longer the duration offlooding, the more extensive the damage will be.

The village of Gowdall is a community that was stillin crisis months after the floods in autumn 2000had abated. Around a hundred homes weredamaged and in March 2001 some homes werestill under several feet of water. The water stayed inGowdall for about two weeks and even threemonths after the flood had receded, Gowdall hadstill not returned to normal. In February 2001 someresidents were told that it would be more than ayear before they would be able to move backhome again. Most people lived in caravans outsidetheir homes while repairs were carried out (BBC,Panorama 2001).

Contamination of floodwater

Floodwater can be contaminated with sewage fromblocked drains and chemicals from people’s garagesor commercial premises that have spilled into thefloodwater. Once floodwater has receded a layer ofcontaminated silt is often left behind. Mould can alsogrow in the damp conditions following flooding.

Contamination can add to the cost of cleaning anddisinfecting buildings that have been flooded.Contaminated floodwater may create some risks tohealth. Protective clothing should be worn during theclean-up operation and other hygiene precautionsshould be taken. Advice on health and safetyprecautions to be taken when restoring floodedbuildings can be found on the Environment Agency’sFloodline website (www.environment agency.gov.uk/flood)and the CIRIA website (www.ciria.org/flooding).

In cases of flooding from the sea, saltwater can leadto corrosion of metallic fittings, including metalducting and switch boxes, and steel reinforcementwithin reinforced concrete. The insurance industry hasestimated that saltwater flooding can increase flooddamage repair costs by around 10%.

19

Once floodwater has

receded a layer of

contaminated silt is often

left behind. Mould can also

grow in the damp

conditions following

flooding.


Other issues

Flooding can also damage property outside thebuilding, such as cars, garages, sheds, gardenfurniture, gardening equipment and garden fences.Patio paving may need to be relaid, and gardenponds cleaned out and restocked.

Rats and other wildlife may also take shelter inproperty in or near flooded areas.

While some furniture, fittings and personalpossessions may dry out after exposure to floodwaterthey may be permanently stained.

20


“We had seen the water rising outside and knew itwould be inside soon but we expected it to comethrough the doorways”, said Carol Mawle fromBanbury in Oxfordshire. “I put towels down to blockthem but it did not help at all. As I heard gurglingnoises from the walls I realised that the water filled theholes in the cavities and then it came through the skirtingboards of the floor. It was eerie. One minute we weredry, the next minute we were walking on a moving carpet.”

By 3am she was forced to leave the bungalow. Herdogs were swimming in a river of sewage. “We liveso far away from the river that even in our wildestdreams we didn’t expect this to happen to us.” Carol and her husband returned to the bungalow ataround 8am to see the water receding and the dirt,covering everything like a layer of film, becamevisible. “The shock doesn’t hit you until you realisethat it wasn’t something that would disappear in aday”, continues Carol. “Getting water out of yourhouse is relatively easy, the problem starts whenyou’re left with everything wet and ruined. The initialdamage is nothing compared to the problems copingafterwards.”

Carol was lucky because she had an insurance policythat covered her household and its contents. “Welost everything. All our clothes, shoes, videos,cameras, kitchen electrical equipment, fridge,washing machine, dishwasher, all lost. I did a lot oftapestries as a hobby, they were all gone too, as theywere kept in the bottom drawer.”

The only things Carol saved was the television andvideo recorder, as she had put them on the bed whenthe water first started to seep in, plus, the kitchenchairs which went on top of the kitchen table, and aset of glass coffee tables.

“The biggest loss was my photographs – favouritemoments of the years gone by were lost and youcannot bring them back. I also had a painting fromsomeone who has since died and although it did notget destroyed, it has watermarks on it and the paintis peeling.“

21

CaseStudyCS


Carol’s insurance policy covered the damage so shecould get the bungalow renovated and decoratedand was able to buy new furnishings, equipment andfurniture, but she says it is not the same living in ahome without the memories.

“You work over the years and save up to buy bit bybit, so the reward of your work is visible in yoursurroundings. In 24 hours it’s all wiped out, all gone.We could at least pay for everything from theinsurance money but I know others might not be solucky as they might choose not to include everythingin the policy.”

Carol is more careful now and she keeps her personalbelongings in top drawers and cupboards. The floodshit her bungalow too fast to even think of what sheshould do to reduce the damage. Now she knowsthat if she had put her photographs, paintings andmost precious and valuable belongings up high shecould have saved them. “There’s only so much youcan do in a state of shock, especially in a bungalow.This is why it is most important to be prepared.”

Source: Environment Agency

22

“You work over the years

and save up to buy bit by

bit, so the reward of your

work is visible in your

surroundings. In 24 hours

it’s all wiped out, all gone.”


Flooding can happen without much warning, asresidents in Edinburgh’s Stockbridge area found outin April 2000. However, they have used theexperience to their benefit and have formed anaction group to educate themselves on all aspects offlooding to help prevent them from being caught outagain.

Built around 1860 to provide housing away from theslums of Edinburgh, the Stockbridge Colonies have avillage air with rows of neat Victorian B listed two-storey flats. Although the current residents, around380 in all, are modern city dwellers who relish theculture that Edinburgh provides, not much haschanged the peace and tranquillity of the area overthe past 140 years. Until one rainy night in April2000 that is…

The rain started gently but by next day had turnedinto a downpour. Residents near the River Leith couldsee that it was rising fast. People were concerned butthe river had always been there and it had neverflooded for at least 120 years. Why would this onebe any different? However, by one o’clock in themorning the peace of the area was shattered. Anumber of streets were in chaos as residentsstruggled to find sandbags to protect their propertyfrom the rising water, with some even digging uptheir gardens and putting the earth in black plasticbags to keep the water out of their homes.

The next morning those who had been floodedreturned to witness what remained of theirproperties. Although only a few streets in the areahad been hit badly, 50 people had been madehomeless. One ground floor flat had only six inchesof water throughout but it took a dehumidifier over2 months, 24 hours a day to dry out the plaster onthe walls. People still find it hard to talk about theirreplaceable personal possessions lost. Over a yearlater, only 75 percent of those left homeless wereback in their homes with the others still waiting forrebuilding work to be completed.

23

CaseStudyCS


While the peaceful ambience of the area hasreturned, the experience has left the inhabitantsdetermined to take action. The local residentsassociation spoke to other local victims of flooding inEdinburgh about their experiences and in December2000 the Edinburgh Flood Prevention Group wasformed. To date the group has had presentationsfrom SEPA hydrologists, Edinburgh City Council,Scottish Natural Heritage and an insurance company.For those who can’t attend the meetings, Newsline, aneighbourhood newsletter provides the 380 flats withall the information they need to know. On a brightsunny day it is hard to believe that the floods reallyhappened. The group feel that way too but aredetermined to keep the momentum of the floodeducation programme going so that their experiencesand the lessons learned are not forgotten.

Source: Scottish Environmental Protection Agency

24

On a bright sunny day it is

hard to believe that the

floods really happened.

Existing Property Owners

Assessing the risk of flooding

Before considering ways to protect your propertyagainst flooding it is essential to assess the flood risk.

Flood risk for a property is a combination of boththe likelihood of flooding occurring (how likely is itthat flooding will affect the property?) and theconsequence of flooding (what is the potentialdamage or impact that could be caused?) Thehigher the likelihood and impact of flooding, thehigher the level of flood risk.

Once the level of flood risk for the property isunderstood, more effective decisions can be madeabout the type of flood protection measures to install.

How to assess the likelihood of flooding

To assess the likelihood or probability of floodingaffecting your property, first consider thesurrounding area:

• Is the property near a river, stream or ditch?

• Is the land in a hollow or at the bottom of a hillwhere floodwater could collect?

• Is the area at risk from flooding from the sea?

• Is the area at risk from groundwater flooding?

• Do river or coastal flood defences protect your property?

As much information as possible should also beobtained on the history of flooding in your area.

• How many floods have occurred in your local areain the past and what were the flood levels inrelation to your property? You may have directexperience of flooding in your property, but youshould also be aware of previous floods thathappened before you moved in, that may havereached even higher levels.

25

Existing Property Owners3


• What was the source of the flooding? For examplefrom rivers, the sea or localised flooding fromblocked or overloaded drains or sewers?

• Is the property protected by existing river or coastalflood defences? Have there been any recentimprovement works that may have reduced yourflood risk, and are any further works planned?

Where can I find information on flood history?

There are a number of sources of informationdepending on the type and severity of flooding.

An important source of information will be yourfriends and neighbours who have lived in the area fora long time, community groups, parish councils andflood action groups. It may also be worth a visit tothe local history section of your local library to lookfor old photographs and reports.

This source of information is very important if you arenew to the area or if your property was only builtrecently, as the local community will have historicknowledge of the area before the development.

You can also contact the following organisations forinformation:

The Environment Agency

The Environment Agency works to preventdevelopment in flood prone areas and in locationsthat may increase the risk of flooding to others. Theoperational role of the Agency is to provide a floodwarning service for flooding from rivers and the seain England and Wales, working together with theemergency services and local authorities whenflooding occurs. It provides and maintains flooddefences along more than 34,000 km of rivers andcoastline. The Agency operates a 24 hour Floodlineservice on 0845 988 1188 that provides a usefulsource of information when investigating whether aparticular location is at risk of flooding. You can alsocall Floodline and listen to any flood warnings thatare in force in your area. Trained Floodline operatorscan also provide you with immediate practical adviceon what to do before, during and after a flood.

26

An important source of

information will be your

friends and neighbours who

have lived in the area for a

long time, community

groups, parish councils and

flood action groups.


The Environment Agency’s indicative floodplain mapsprovide a general overview of areas of land in naturalfloodplains that are at risk of flooding from rivers orthe sea. The maps use the best information availablebased on historical flood records and computermodels of river flows. They indicate where there maybe a risk of flooding from rivers, streams, otherwatercourses or from the sea. However, these mapsdo not cover flooding from other sources such asgroundwater flooding, burst water mains, roaddrains, run-off from hillsides, or sewer overflows, asthis type of flooding can occur almost anywheredepending on the pattern of rainfall. The mapsindicate the risk of flooding within the natural flood-plain and do not take account of protection providedby man made flood defences.

Flood mapping is not a precise science. The mapsonly provide an indication of areas that could flood inthe event of extremely bad weather. For example,they show the extent of river flooding that couldoccur once in 100 years – or in other words a floodwith a 1 per cent chance of happening in any oneyear. For flooding from the sea and tidal estuaries,the maps indicate a 1 in 200 year return period, i.e. aflood with a 0.5 per cent chance of happening in anyone year. It is important to remember that returnperiods are averages. Floods can occur in successiveyears or more than once in one year – the riskremains there all the time. For example there were 30floods in the 30 months between December 1997and June 2000.

For further information call the Environment Agency’sFloodline on 0845 988 1188 or visit their website(www.environment-agency.gov.uk/floodline). Theindicative floodplain maps can be viewed on thewebsite or obtained from Agency local officesthrough Floodline.

27

The maps use the best

information available based

on historical flood records

and computer models of

river flows. They indicate

where there may be a risk of

flooding from rivers,

streams, other watercourses

or from the sea.


Flood warnings

The Environment Agency provides a flood warningservice in England and Wales and supports the publictaking action to prepare and respond when thesewarnings are issued. The warnings are provided forflooding from rivers and the sea but not for localisedflash flooding that cannot be predicted, for examplefrom blocked or overloaded sewers or localgroundwater flooding.

The Environment Agency issues warnings through themedia on TV and radio weather bulletins and on itswebsite (www.environment-agency.gov.uk/floodline).In areas of particular risk, the Environment Agencycan send a warning message direct to people athome or at work by telephone, fax or pager using anAutomatic Voice Messaging (AVM) system. Sirens andflood warden schemes may also operate, particularlyin flood prone urban areas.

The Environment Agency’s Floodline 0845 988 1188service for England and Wales carries recordedinformation on flood warnings in force anywhere inEngland and Wales. The information is regularlyupdated and is available 24 hours a day.

The Floodline service which has been operational inEngland and Wales for several years has now beenextended by the Scottish Environment ProtectionAgency (SEPA) to cover the whole of Scotland. Aswell as providing the latest information on thepossible risk of flooding throughout Scotland 24hours a day, anyone concerned about flooding cancall the Floodline service for general advice andguidance on flooding. In a similar role to that of theEnvironment Agency in England and Wales, SEPAseek to avoid inappropriate development within thefloodplain that could lead to increased flood risk.

Local authorities and building control bodies

Local planning authorities can also provide a range ofuseful information. They have a number of plans anddocuments that provide information on local flooddefences and land-use planning and should also have

28

In areas of particular risk,

the Environment Agency can

send a warning message

direct to people at home or

at work by telephone, fax or

pager using an Automatic

Voice Messaging (AVM)

system.


information on past flooding events. Local authoritiesprovide and maintain flood defences on localwatercourses and are responsible for controllingdevelopment within the floodplain and elsewherewithin river catchments. The Building Control andHighway departments (or approved private sectorbodies) may have information on more localisedfloods such as those caused by ditches, streams andthe local drainage system. Water and seweragecompanies may also be able to provide informationon localised flooding from sewers.

Are flooding measures required?

If a property is at very low risk of flooding then stepsto improve flood resistance are clearly unnecessary.The following list of general questions can help toassess whether flood protection measures, as set outlater within this guide, are worth considering for aparticular property:

• Has the property or surrounding land and gardensever flooded in the past?

• Have neighbouring properties ever flooded?

• Is the property in a floodplain?

• Has the property been issued with a flood warning?

• Is the property close to a surface water drainageditch or stream that could overflow?

• Is the property in a hollow or low-lying area?

• Is the property protected by river or coastaldefences?

If you have answered “No” to all of these questionsthe risk of flooding affecting your property is smalland flood resistance measures are unlikely to benecessary. Conversely if you have answered “Yes” toone or more of these questions then implementingsome of the measures outlined in this guide may wellbe beneficial.

29

Local authorities provide

and maintain flood defences

on local watercourses and

are responsible for

controlling development

within the floodplain and

elsewhere within river

catchments.


The consequences of flooding

The consequences or impacts of flooding in terms offlood damage and the associated stress caused byflooding have been discussed above in Section 2. The potential flood repair costs associated with thebuilding, and replacement costs for personalpossessions and business stock, can only beconsidered once the likely frequency and depth offlooding are known.

A summary of the key elements in assessing the floodrisk for a particular domestic or small businessproperty are illustrated by the flowchart on page 31.

Deciding what flood level to defend against

The following sections within this guide discuss themeasures that can be taken to protect propertyagainst flooding. The measure or combination ofmeasures chosen will depend upon the depth towhich the property could be flooded and theflooding frequency. The case study on page 32gives an actual example of how a householder hasassessed the flood risk for her property and theappropriate level of protection to adopt.

30

The potential flood repair

costs associated with the

building, and replacement

costs for personal

possessions and business

stock, can only be

considered once the likely

frequency and depth of

flooding are known.


Identify the sourceof the flood risk.

Flood risk – the truecost of flooding.

Assess the cost ofrepairing damage andreplacing belongings ifthe property wasflooded to themaximum flood depth.

Assess the in-directcosts of being flooded,including the stress oflosing belongings,organising repairs andliving in temporaryaccommodation.

Qu

anti

fy t

he

likel

iho

od

Qu

anti

fy t

he

con

seq

uen

ceRisk assessment

How often doesflooding occur?

Maximum depth ofpast floods at the

property?

Damage to propertyand belongings.

Social costs offlooding.

31


“When the floods of autumn 2000 brought 0.5metres of water into my house, I thought it would bewise to look at river levels over a longer period than Ihad personally experienced, and decide what steps Icould reasonably take to minimise damage fromflooding”, said Bewdley resident Gill Holland. “If Iwas going to move the electrical sockets, meters andboiler above the flood level, how was I going todecide how high they should go?”

“It was soon obvious that the records that had beencarefully made by the police and borough councilwere no longer in existence. I phoned theEnvironment Agency and found that their floodwarning section could send me a graph of local floodlevels going back to 1925. If I had wantedinformation on Shrewsbury or Worcester, that wouldhave gone back even further, 300 years or so. I thinkon the whole 75 years (a lifetime) is enough to givean idea of the extremes. I was delighted to find thatthe exact information I wanted was freely available.The office couldn’t have been more helpful. Thegraph is very sobering. The normal pattern is forregular flooding of houses in the town. The floodsare not exactly cyclical, but the peaks seem to bebunched into groups. The flood of 1947, 0.28 metresabove the level I have just experienced, is alwaysquoted locally as the worst in living memory. Thelevel reached in 1946 was only a little less but isnever mentioned.”

“To find out the effect that such a major flood hadon the community, I went to look at copies of thelocal papers, which are held on microfilm at a localbranch of the county library. These make fascinatingreading, if only to put things in proportion. TheCounty Record Office has, in our case, very littlewritten evidence on floods, but better photographicevidence. The local Civic Society also has a largecollection of old photographs of the town which givean accurate idea of the extent of the water up themain street in 1947.”

“I would now be sceptical about most verbalaccounts of the height of the flood. After the 1947flood, height markers were mounted on quite a few

32

CaseStudyCS


houses. These were still there in the 1960s, but haveby now all been taken down by occupiers keen to selltheir properties. This has led to some wildlyexaggerated claims of the flood height. People havedescribed how the water was licking the ceilings ofthe houses, when it is clear that it could not havebeen much more than halfway up the windows.With this in mind, I think I should be looking not justat the 2000 level, which was 0.5 metres in my house,but should think how I would survive at least the1947 level which was 0.78 metres. This is the level,which the Environment Agency is taking as the 1 in100 year flood in my area, and up to last yearseemed improbable. I am not so certain now.”

“Some precautions are easily taken. It is not thatexpensive or inconvenient to have sockets a metre offfloor level. Moving an electric meter is moreexpensive, but worth it to maintain supply upstairsfor heating and lighting during and after a flood.Moving my existing gas boiler would be moredifficult, as the plumbing system sets a limit on howhigh you can raise it. It seems at this stage better toleave it in position until it suffers one flood too manyand it can’t be resuscitated, and then replace it witha smaller, more efficient modern boiler set higher up,or even on the first floor. I think you’re likely toreview your own situation in a different way,depending on what you can afford, your lifestyle, andindeed how you see the risks during your lifetime butthrough some simple research and fact finding, youcan significantly reduce the consequences of yourproperty being flooded.”

Source: Gillian Holland

33

Remember that all gas and

electrical appliances that

have come into contact with

floodwater must be

inspected by a qualified

engineer before they are

re-used.


Prepare a Flood Plan!

As well as the measures set out later in this guide tomake the property more flood resistant, it is alsoessential to prepare a flood plan so that you knowwhat immediate steps to take should a flood occur.The Environment Agency has produced a number ofuseful checklists which are included at the end of thisguide in Section 8. Updated versions can be found onthe Floodline website.

34


Roger Dixon, a solicitor, is no stranger to the misery aflood can bring. In March 1999 his office at StamfordBridge was flooded for a week when the RiverDerwent burst its banks. More than a year on, anindustrial dehumidifier was still at work in thebuilding.

Before the Stamford Bridge flood, his firm inCumberland Street, York, was seriously damaged byfloods in 1981 causing loss of business and hugeinsurance claims. Since then the office has sufferedflooding two or three more times. “Stamford Bridgewas unaffected – but it was touch and go at the Yorkoffice. There was about three inches to go before theundercroft would have flooded. But we had ourcontingency plans in place,” said Roger.

Since being flooded in the 1980s, the firm hasadopted a ‘be prepared’ policy. Storm lanterns, non-electric heaters and camping stoves are all kept at theoffices.

“Floods do happen to you,” said Roger. “No-one isto blame for the elements but with an advancedwarning system and a flood plan you can minimisethe damage. When it rains heavily now, we don’t justsit there remarking on the weather. We have a teamof people responsible for finding out exactly what’shappening weather-wise”. We have educatedourselves and we can generally work out how highthe river is likely to rise and what the critical levelsare. We know what organisations are responsible forwhat and we take action.”

Source: Environment Agency

35

CaseStudyCS

Carpets will normally need

to be replaced following

immersion in floodwater

although specialist cleaning

services are available.

Consider using loose fitting

rugs that can be moved and

stored upstairs before

flooding occurs.


Choosing the right options Once the flood risk has been assessed the measuresfor protecting the property can be considered. It isessential that the nature and depth of flooding isproperly assessed before any improvement measuresare considered, otherwise the most appropriate andcost effective option for the property may not bechosen. Information related to this is given on theCIRIA website (www.ciria.org/flooding) in a series ofadvice sheets on improving the overall floodresistance of a property, and in the EnvironmentAgency leaflet ‘Flood Products’, which is availablethrough Floodline 0845 988 1188.

Where can floodwater enter my property?Floodwater can find its way into properties through avariety of routes including:

• Ingress around closed doorways.

• Ingress through airbricks and up through theground floor.

• Backflow through overloaded sewers discharginginside the property through ground floor toilets andsinks.

• Seepage through the external walls.

• Seepage through the ground and up through theground floor.

• Ingress around cable services through external walls.

To reduce the likelihood of floodwater entering theproperty it is important to identify where the potentialpoints of entry are located. The flooding routes willdepend on the type of construction, the underlyingground conditions and the expected flood depth.

For example airbricks below ground floor level arenormally only found in properties with suspendedfloors to allow the void under the floor to beventilated. Other wall vents above the ground floor arelikely to be present if gas appliances are in the room. Ifsinks and downstairs toilets are located below theexpected flood depth it is possible that floodwater willflow back through the sewers and into the property,unless non-return valves are installed.

36

Backflow through surcharged drains

Water ingress at doors and windows

Ground seepage Water ingress through airbricks and other wall vents

Seepage throughcracks and jointsin walls and gaps around servicepipes and cables

Seepage through the external walls will depend uponthe flooding duration and the type of constructionand condition of the wall. Water will tend to find itsway through weak points within the wall such ascracks and voids in the mortar jointing, brickwork orrendering. For semidetached and terraced houses it isimportant to remember that floodwater may alsoseep through adjoining party walls with neighbouringproperties, above or below floor level.

Depending on the permeability of the ground underthe property, floodwater may seep through theground and up through gaps or cracks in floors orother weak points. The actual rate of seepage isdifficult to estimate, as this will depend on the typeof ground, the duration of the flooding and theconstruction of the property.

If your property has flooded in the past then you mayalready know where the entry points are located butit is recommended that these are reconsideredcarefully before any measures to reduce the impact offlooding are taken.

What measures could be taken to improve theflood resistance of the property?

There are many measures that can be taken toreduce the impact of flooding on the home orbusiness property. These measures generally fallwithin two main categories, those that are taken tokeep water out of the building, often called dry-proofing measures, and those to improve the abilityof the property to withstand the effects of floodingonce water has entered the building, known as wet-proofing.

Dry-proofing measures include moveable floodprotection barriers for doorways, low level windowsand other openings that can be installed before thearrival of floodwaters, and the installation of non-return valves on sewers to prevent backflow.


37

Valve to preventbackflow

Flood barriersfor doorways

Covers forairbricks andother wall vents

Improved flood resistance ofexternal walls and floors toprevent water ingress

Dry-proof measures


Wet-proofing measures include the use of floodresistant building materials within walls and floorsand in other parts of the structure, and the raising ofelectrical wiring above flood levels.

The measure or combination of measures chosen willbe dependent on the depth and frequency offlooding. The following sections provide more detailon the measures available for both keeping the waterout of the property (dry-proofing) and improving theflood resistance of the building elements (wet-proofing).It is recommended that all the dry-proofing and wet-proofing systems mentioned in this guide areconsidered so that the most appropriate measures foryour particular circumstances can be identified.

Cost implications of flood protection measures

The cost of improving the flood protection of aproperty will vary depending on many factorsincluding the flood depth, property size, constructiontype, internal finishes, and the location and type offittings and services. It is therefore difficult to provideany meaningful cost figures within this guide forcomparative purposes, however some usefulinformation is given in the ABI 2003 report on thecost and effectiveness of flood resistant measures.

When considering flood resistance measures the costsof installation needs to be weighed against thepotential cost savings that such measures couldprovide in terms of reduced repair costs, lowertemporary accommodation charges, and reducedbusiness losses following future flood events.

In the majority of cases taking steps to improve theflood resistance of properties at risk of flooding willprovide long term financial cost savings in addition toreduced levels of stress experienced when floodingoccurs.

Property audit tableBefore considering the various measures set out in thefollowing sections of this guide, the following tablecan be used as a simple property audit to help identifywhich measures may be appropriate for your property.

38

In the majority of cases

taking steps to improve the

flood resistance of

properties at risk of flooding

will provide long term

financial cost savings in

addition to reduced levels of

stress experienced when

flooding occurs.

Improved resistance of internal walls,floors and fittings to improve the ability of

p ,

materials to withstgg

and the efp

fectff s of internal flooding

Raiseelectricalsocketsaboveflood level

Wet-proof measures


39

Question Consequence

For semidetached and terraced houses, floodwater may seepthrough adjoining party walls. In bungalows it will be more difficult to move personalpossessions above the flood level.

With permeable ground conditions floodwater is more likely toseep up through floors, and flood barriers are less likely to beeffective (Section 4).

Standard flood barriers are available for doors, windows andairbricks. Longer span barriers will be needed for largerwindows and patio doors.

It may not be possible to preventing floodwater enteringconservatories.

Specialist advice must be obtained before undertaking anymeasures to prevent water ingress to basements (Section 5).

Cracks to walls and render can be repaired to reducefloodwater seepage.

The type of wall and surface finish affects the type of floodresistance measures that can be carried out. More detailedadvice is given later under Section 5.

The floor type is also important when considering improvingflood resistance. More detailed advice is given later underSection 5.

Services can be raised above flood levels.Kitchen units of chipboard or MDF usually require replacementif exposed to floodwater. Units can be raised on plastic legs.More detailed advice is given later under Section 5.

House type?• Detached.• Semidetached.• Terrace.• Bungalow.

Ground type?• Permeable (Chalk or gravel).• Impermeable (clay soils).

Routes of entry for floodwater?• How many external doors are

there?• Do you have patio doors?• Is there a connecting door to the

garage?• Do you have a conservatory?• Are there any airbricks or vents

below the flood level?• Are there any cables or pipes

passing through the walls?

Do you have a basement or cellar?

Condition of external walls?

Type of external wall? • Solid masonry, cavity, timber-

framed, half-timbered.

Type of internal wall? • Solid masonry, stud partitions,

timber framed.

Type of external wall finish?• Painted or rendered.

Type of internal wall finishes? • Plaster, plasterboard.• Painted, wallpapered.

Floor type?• Suspended timber, solid concrete,

suspended concrete.

Fittings and services?• Height of boiler, consumer unit

(fuse box), electrical sockets andgas meter above flood level?

• Type of kitchen units/cupboards?


Keeping the water out using floodbarriers

Introduction

Keeping water out of a property, or limiting theingress of floodwater, should always be the firstpriority when considering flood protection measures.Excluding water will help to reduce damage to theinternal fabric of the building and its contents thusreducing the associated stress and suffering ofhouseholders and business users. These measures areoften called dry-proofing and include:

• Temporary flood barriers.

• Measures to reduce seepage through walls andfloors.

• The installation of non-return valves on sewers.

Movable flood barriers can be very effective inpreventing or reducing the volume of floodwaterentering through doors and other external openingsin walls, such as windows and airbricks, as long as agood quality product is installed in accordance withthe manufacturer’s instructions.

Although barriers may not totally prevent the ingressof water into a building, as seepage may still occurthrough the floor or walls, they can provide valuabletime in which to move personal possessions to higherlevels before floodwater rises inside the building.Flood barriers on wall openings can also reduce theamount of contaminated silt and debris entering theproperty. Water that seeps through the ground orwalls is likely to be filtered to some extent andtherefore is usually cleaner than floodwater enteringlarger openings such as gaps around doors andairbricks.

Permanent measures to reduce seepage throughwalls and floors are covered later within this guideunder Section 5. The actual rate of seepage willdepend upon the building’s construction, the groundconditions and the duration of flooding. It should

40

Excluding water will help to

reduce damage to the

internal fabric of the

building and its contents

thus reducing the associated

stress and suffering of

householders and business

users.


also be remembered that in certain circumstancesfloodwater can backflow through sewers intoproperties unless non-return valves are installed.Guidance on the installation of these valves is alsoincluded in Section 5.

Taking action to erect flood barriers

Although temporary barriers have a number ofbenefits they rely on the householder taking positiveaction in good time before the floodwaters arrive.If householders or business users are away from theproperty at the time of the flooding (for example onholiday), or if the barriers are not erected quicklyenough following a flood warning, such temporarymeasures will provide no protection against flooding.Barriers may also not be suitable for use by vulnerablemembers of society who are not physically able touse them unless friends or family are at hand to help.

Remove all barriers after use!

Once the floodwaters have subsided it is veryimportant that all temporary covers to airbricksand other vents through external walls areremoved. Airbricks play a vital role in providing aflow of air beneath suspended floors to preventcondensation and possible decay of the structure.They are also required to disperse any build up ofdangerous gases that could collect within the sub-floor void.

Vents through external walls are often required abovefloor level in rooms with gas appliances to avoid anydangerous build up of carbon monoxide. Floodbarriers to such vents must be removed before gasappliances are switched back on. Keep a list of allvents that have been temporarily blocked before theflood so that they can be removed after thefloodwater recedes, but keep listening for furtherflood warnings from the Environment Agency.

What is the maximum barrier height?

When deciding whether to install flood barriers it isimportant to consider the expected flooding depth.

41

Flood barrier strong enoughto withstand the pressure offloodwater

Maximumheight ofprotection

Airbrick cover


Care must be taken to ensure that the external wallsof your property are strong enough to withstand theweight of floodwater, which increases with depth.For example floodwater 1 metre deep on the outsidea building (with no water inside the property) willexert a force of around half a tonne on an externaldoor.

For most properties the external walls should havesufficient strength to retain flood depths up to900mm (3 feet) above external ground level, with nowater inside the building. However, the actual waterlevel that can be safely retained by the external wallswill depend upon the construction, age and conditionof the walls. For expected flood depths between600mm and 900mm above external ground level(2 to 3 feet) it is recommended that the externalwalls are inspected by a qualified building surveyor,architect or structural engineer, before any barriersystem is installed. Similarly windows and patio doorshave limited strength and must not be relied upon towithstand the pressure of floodwater, unless they arealso protected with a robust barrier system.Floodwater can burst through unprotected windowsand glazed doors.

If the maximum expected flood level is above the saferetention level for the walls (normally up to 3 ft) ithas to be accepted that floodwater will enter theproperty should a flooding event of this magnitudeoccur. However, it should be borne in mind thatflooding depths vary in accordance with weatherconditions. Therefore although the maximumexpected flooding event may be above the saferetention level, flood barriers may still be effective forother shallower flooding events below this level. Thevariability in flood depth is therefore another keyissue when deciding whether temporary floodbarriers are suitable for your property.

42


What types of barrier system are available?

There are a number of flood barrier productsavailable in the UK (see Enviroment Agency leaflet on‘Flood Products’). The main types are as follows:

Barriers for external doors Barriers for external doors usually take the form ofplastic or aluminium flood boards that can be quicklyinstalled across a doorway in advance of floodwatersarriving. The flood boards normally slide into a frameattached around the doorframe to provide awatertight seal. After the floodwater has receded theboards can then be removed, cleaned and stored forre-use.

Barriers for windows and patio doorsBarriers for windows and patio doors are similar tothose for external doors. Flood boards, or beams forwider openings, are normally dropped into a frameattached around the opening. Such systems can alsobe used for shop windows and garage doors.

Airbrick coversA number of plastic covers are available that can befixed over airbricks and other vents in external walls.Such covers are usually clipped into a frame fixedaround the airbrick or vent opening. As discussedabove it is very important to remove such barriersonce floodwaters have subsided.

Flexible skirting systems As well as flood barriers for doors, windows and air-bricks, more advanced systems are available forenclosing the bottom 600mm to 900mm of buildingswith flexible plastic skirting to prevent the ingress offloodwater. The plastic skirting can be housed inunderground ducts and then lifted up to protect thewalls in advance of a flood. Such methods are likelyto be expensive to install but could be beneficial incertain circumstances, such as for detachedproperties that are regularly flooded.

43

Frame

Frame

Board

Sliding panel acrossan entrance

Airbrick cover clipped into frame

Frame


Flood barrier manufacturersContact details for manufacturers of temporarybarrier systems are listed on the National FloodForum’s website (www.floodforum.org.uk). Thosewith the Kitemark are listed on the EnvironmentAgency’s website (www.environment-agency.gov.uk/floodline).

It is recommended that a number of manufacturersare approached so that the most appropriate systemfor the property can be identified. When choosing abarrier system make sure that the product is suitablefor sealing the type of openings on your property,and is adequate to withstand the maximum expectedflood depth. Ask for a demonstration beforepurchasing any system to ensure it can be fittedquickly and effectively.

Standards for flood protection productsA new British Kitemark standard has been establishedfor the flood protection products described above, aswell as for temporary freestanding barriers (seebelow). The Kitemark award certifies that the producthas been rigorously tested to ensure that it is fit forpurpose if installed and used in accordance with themanufacturer’s or supplier’s instructions.

Sandbags As well as manufactured flood barrier products,sandbags can be effective in reducing the ingress offloodwater into buildings and are still widely used.The Environment Agency has produced separateadvice on how sandbags should be used, and onalternatives such as earth filled bags. Details can befound within the Agency’s leaflet ‘Damage Limitation’and on their Floodline website. The leaflet also givesadvice on how to make home-made flood boards.

Temporary freestanding flood barriers erectedaway from buildings All the barrier solutions described above are forinstallation around single buildings, to block doors,windows, and other wall openings.

44

When choosing a barrier

system make sure that the

product is suitable for

sealing the type of openings

on your property, and is

adequate to withstand the

maximum expected flood

depth.


In addition to these measures for single buildings,there are a number of available barrier systems thatcan be erected away from buildings to protect groupsof properties or surrounding land and gardens.Guidance on the use of these types of remote barrieris provided in the Environment Agency leaflet on‘Flood products’ and the seperate guide on‘Temporary and Demountable Defences’. Such barriersystems require careful selection and installation.

In certain circumstances where investment inconventional flood defences cannot be justifiedeconomically, or where there is an immediate needfor protection, local authorities may consider the useof such temporary barriers to protect small groups ofexisting properties.

National Flood ForumThe National Flood Forum are a national organisationworking with and representing those at risk offlooding. They can offer support to those affected byflooding including general information about all typesof flood products, possible sources of help andstrategies for coping. Visit the NFF website(www.floodforum.org.uk) or contact them on 01299403055.

45

The Environment Agency

has produced separate

advice on how sandbags

should be used, and on

alternatives such as earth

filled bags.


Other permanent measures toimprove flood resistance of propertyAs discussed above it has to be accepted thatfloodwaters will enter a property if the flood depth isgreater than the safe retention height for temporarybarriers. Even in areas of shallow flooding, water maystill enter properties unless suitable barrier systemscan be put in place in good time. Seepage is alsolikely to occur through floors and walls depending onthe type of construction, the ground conditions andthe duration of flooding.

In these circumstances, due to excessive flood depth,uncertainty over whether barrier systems could beinstalled in time, or seepage through floors and walls,there are a number of measures that can be taken toimprove the flood resistance of the internal buildingelements. These measures, often described as wet-proofing, can significantly reduce the cost of repairsfollowing internal property flooding and can speedup restoration times. There are two main occasionswhen householders or business owners mightconsider adopting these measures:

1) When restoring a building after it has beenflooded.

2) As part of planned improvement works, includingnew extensions.

After a property has been flooded the opportunitycan be taken to replace damaged elements such aswall plaster, flooring materials and kitchen units withmore flood resistant materials. Should flooding occuragain the property will then suffer less damage andshould dry out more quickly.

Similarly if you have suffered from flooding in thepast or live in an area at risk of flooding and you areplanning to carry out improvement works such as anew kitchen, or extension, this would be a good timeto build in flood resistant measures.

The different elements of the building fabric that canbe improved to resist the effects of flooding arediscussed in detail under Section 5.

46

After a property has been

flooded the opportunity can

be taken to replace

damaged elements such as

wall plaster, flooring

materials and kitchen units

with more flood resistant

materials.


It should be noted that the guidance provided withinSection 5 is of a more technical nature than previoussections. Professional advice should always beobtained before any improvement measures includedwithin this guide are carried out. When handlingbuilding materials care should also be taken to followmanufacturer’s health and safety instructions.

Building warrantiesIf you live in a new house that has been built withinthe last 10 years, your property may have insurancecover for protection against building defects, such as‘Buildmark’ cover given by the National HouseBuilding Council (NHBC). Similar cover may also applyto new extensions.

If this type of insurance applies to your property, it isimportant to read the terms of the policy and checkwith the insurance provider before carrying out anymeasures to improve flood resistance.

Historic buildingsMany of the properties affected by the autumn 2000floods were historic buildings. These can be statutorylisted buildings, unlisted buildings in conservationareas, locally listed buildings or buildings ofarchitectural or historic interest. These properties areoften more vulnerable to flood damage, particularlythe stone-work, brick and mortar walls, timberframes, wattle-and-daub panels, timber boarding andpanelling, earthen walls and floors, plaster, ceilingsand many decorative finishes.

English Heritage is currently producing guidance inthe form of a Technical Advisory Note (Flooding andHistoric Buildings) for those whose property may be atrisk from flooding. Interim guidance for historic buildingsis already available on the English Heritage website:(www.english-heritage.org.uk). The equivalentbodies to English Heritage in Scotland and Wales areHistoric Scotland and Cadw (Welsh Heritage).

47

Many of the properties

affected by the autumn

2000 floods were historic

buildings. These can be

statutory listed buildings,

unlisted buildings in

conservation areas, locally

listed buildings or buildings

of architectural or historic

interest.


The following section summarises some of the keypoints raised by English Heritage but it isrecommended that the local authority conservationofficer should be contacted in the first instance if ahistoric property has been, or is likely to be,inundated by floodwater.

• Flood protection measures must not damage thespecial interest or the integrity of the building. Inparticular, the existing structure, materials andappearance must be retained and respected. Thematerials and techniques used should be traditionaland compatible with existing ones and anyalterations should be detectable and reversible.

• Works that materially affect the character orappearance of a listed building, be they floodprevention barrier installations, or the removal andreplacement of parts of the building fabricfollowing flooding, may require consent from thelocal planning authority. Early consultationbeforehand is recommended. Similarly, works thataffect the external character or appearance ofunlisted buildings in conservation areas may needplanning permission.

• Historic property owners need to be more aware ofthe extra damage that can be caused by theunauthorised removal and disposal of wet timberpanelling and removal of plaster wall coveringsfrom listed buildings. In some cases the flooddamage responses advised by cleansing contractors,insurance companies and loss adjusters can result infurther damage. It is recommended that your localplanning department’s conservation officer isconsulted before consenting to any ‘clean-up’ or‘drying-out’ work.

• Historic materials that may appear to be beyondrestoration can often be restored and reused costeffectively. The first principle of good conservationis to retain as much authentic original fabric aspossible.

48

Historic materials that may

appear to be beyond

restoration can often be

restored and reused cost

effectively.


49

• Grants for emergency works may be available fromEnglish Heritage for the conservation and repair ofnationally important listed buildings after flooding,for specialist works not covered by owners’ floodinsurance. Advice should be sought from the localplanning authority’s conservation officer beforecontacting English Heritage’s regional offices.


50

New Development

51

New Development4IntroductionThis section of the guide has been prepared toprovide supplementary planning guidance for use bydevelopers, local authorities, building control bodiesand others involved with new development in areasof high flood risk, in support of the Government’snew planning guidance on development and floodrisk.

Planning GuidancePlanning Policy Guidance Note 25: Development andFlood Risk (PPG25) was published in July 2001 by theformer Department for Transport, Local Governmentand the Regions (DTLR). The guidance, which appliesonly to England, explains how flood risk should beconsidered at all stages of the planning anddevelopment process in order to reduce futuredamage to property and loss of life. It guides allparties involved in the planning and developmentprocess.

PPG25 requires a precautionary approach to ensurethat any development is safe and not exposedunnecessarily to flooding. The guidance also requiresthat run-off from development should not increaseflood risk elsewhere in the catchment, and thatdevelopment must not constrain the natural functionof the flood plain, either by impeding flood flow orreducing storage capacity. New development shouldtherefore be located in zones of little or no flood riskwherever possible.

Under PPG25 new building works within areas offlood risk are only permitted in exceptional caseswhere the risks are managed and adequate flooddefence measures and/or flood resistant constructiontechniques are adopted. Developments should alsoincorporate sustainable drainage systems wherepracticable and other mitigation measures to avoid


increasing the risk of flooding further downstream.The guidance within PPG25 takes a sequential risk-based approach. New development in high flood riskzones should only be permitted where it can bereasonably demonstrated that lower risk alternativesare not available. The developer must demonstrate tothe local planning authority that the proposeddevelopment fulfils the above requirements.

In Scotland guidance is provided by National PlanningPolicy Guideline NPPG7 – Planning and Floodingwhich was published in 1995 and is available fromthe Scottish Executive. It provides guidance toplanning authorities, developers and the public sothat flood risk can be properly taken into account indevelopment plans and development control. ScottishPlanning Policy 7, Planning and Flooding, was issuedfor consultation in 2003 (SPP7). Separate advice onsustainable drainage is given in Planning Advice Note61 – Planning Sustainable Drainage systems. In Walesnew policy on development and flood risk isemerging through the revision of Technical AdviceNote 15 Development and Flood Risk (TAN 15). SPP7and TAN 15 are expected to be issued in final formduring 2003.

General principles of flood resistantdesign for new developmentWhere new development is proposed within areas ofhigh flood risk, measures are required to reduce theimpact of flooding. Such development can includenew buildings and extensions to existing properties.

Applications for planning permission should beaccompanied by a detailed and robust flood risk andrun-off assessment for the particular site within itshydrological context. This assessment must be basedon up to date information to establish the likelyspeed with which flooding may occur, flow rates,water depth, duration and social and environmentalimpacts. Detailed guidance on how to undertakesuch a risk assessment is provided within PPG25 andby the SEPA Planning Authority Protocol. Completion

52

New development in high

flood risk zones should only

be permitted where it can

be reasonably demonstrated

that lower risk alternatives

are not available.

New Development

of the risk assessment is essential in order that thenature of flooding can be properly taken into accountin the design process.

Ground floor levels

The most important measure that can be taken toreduce the impact of flooding is to raise theminimum floor level of the property ordevelopment above expected flood levels. Thelocal planning authority has the power to impose acondition on planning permissions by specifying aminimum ground floor level.

Clearly there are practical limits to which ground floorraising can be employed if visually obtrusivedevelopment is to be avoided, but it is essential thatfloor levels are fully considered in the design andplanning process. For example on a sloping site itwould be preferable to develop residential housingon higher parts of the site above projected floodlevels and to use lower lying areas for landscape orrecreational areas. For flatter sites it may be possibleto raise ground locally to form higher formation levelsfor new buildings while reducing levels elsewhere onthe site in garden/landscape areas to avoid reducingfloodplain storage volumes. Other options caninclude the provision of flood defences within thelandscaping of the site provided flood storagevolumes are not reduced.

Forms of construction

Some types of construction may present particularproblems for developments in areas of flood riskunless specific measures are adopted. These includesingle storey buildings where occupants will beunable to move themselves or personal possessionsto an upper level at times of flooding, andbasements that could be inundated with floodwater.

Innovative designs where residential living areas areraised to first floor level may be appropriate in somecases, with the ground floor used as garages or

53

The local planning authority

has the power to impose a

condition on planning

permissions by specifying a

minimum ground floor level.


storage accepting that floodwater will enter fromtime to time. However such designs may result inaccess problems when floodwaters rise.

The type of floor construction should also beconsidered. Solid concrete floors are preferable tosuspended floor construction as they can provide aneffective seal against water rising up through thefloor, provided they are adequately designed. Solidconcrete floors generally suffer less damage thansuspended floors and are less expensive and faster torestore following exposure to floodwater.

Detailed measures to improve flood resistance

In addition to adopting appropriate forms ofconstruction and establishing raised ground floorlevels, consideration should also be given toimproving the flood resistance of the building fabricso that flood damage is minimised and properties canbe re-inhabited as quickly as possible afterfloodwaters have subsided. Detailed measures forwalls, floors, building services and fittings are set outwithin Section 5 of this guide. To provide adequateflood protection for new development, local planningauthorities may seek to require such measures byattaching conditions to planning permissions.

Interface with Building RegulationsThe Building Regulations are made to securereasonable standards of health and safety, welfareand convenience of people in and around buildings.

The Building Regulations cannot be made forpurposes of property protection. However, whereflooding may have implications for health or safety,appropriate guidance may be given in supportingdocuments.

54

Solid concrete floors are

preferable to suspended

floor construction as they

can provide an effective seal

against water rising up

through the floor, provided

they are adequately

designed.

Permanent Measures to Reduce Flood Damage

Introduction

This section of the guidance provides information onthe wide range of permanent measures that can beundertaken to improve the flood resistance of newand existing buildings. These measures can help toreduce the extent of flood damage, thereby reducingrepair costs and speeding up building restorationtimes. Four sub-sections are provided coveringimprovements to:

• External walls.

• Internal walls.

• Floors.

• Building services and fittings.

Whilst this section of the guidance is aimedprincipally at existing property owners it should alsohelp to raise awareness of the flood resistance measuresthat can be adopted in the design and constructionof new properties. Advice sheets on improving theoverall flood resistance of a property are available onthe CIRIA website (www.ciria.org/flooding). The useof temporary flood barrier systems for buildings isdiscussed in Section 3 and is not referred to withinthis part of the guide.

It should be noted that the guidance provided inthis part of the guide is of a more technicalnature than previous sections. Professionaladvice should always be obtained before anyimprovement measures contained within thisguide are undertaken. When handling buildingmaterials care should also be taken to followmanufacturer’s health and safety instructions.

Some flood resistance measures discussed withinthis section may require building control

55

Permanent Measures to Reduce FloodDamage – New and Existing Properties5

It should be noted that theillustrations contained within thissection of the guide are included todemonstrate the main differencesbetween the most common wall andfloor types found within domesticproperties. They are not drawn toscale and are included for generalinformation purposes only.


approval, depending on the type of propertyconcerned. If in doubt advice should be soughtfrom the local building control officer.

External walls

Introduction

A number of different external wall types are foundwithin domestic and small business properties acrossthe UK including solid masonry walls, cavity walls,timber-framed walls, and half-timbered walls. Beforeconsidering flood improvement measures it isnecessary to establish the type of wall, if necessary byseeking professional advice.

Please note that guidance on improving the floodresistance of half-timbered walls, which arenormally found in historic buildings, is not providedwithin this guide. English Heritage is currentlyproducing guidance in the form of a TechnicalAdvisory Note (see page 47).

The outside face of external walls

The outside face of most external walls is normallyconstructed of brickwork, which is either left exposed(fair faced), rendered and or/painted. For existingproperties, cracks within the brickwork joints orrender below the expected maximum flood levelshould be repaired to reduce the amount of seepagethrough the wall.

A variety of water-resistant paints and coatings (ortanking) are available that can help preventfloodwater soaking into the external face of the wall,thus allowing the wall to dry out more quickly.Specialist advice must always be obtained to ensurethat the most appropriate system is chosen for theproperty. Coatings should be applied to 500mmabove the maximum expected level of flooding. Anymeasures to improve water resistance must becompatible with the existing wall materials and mustallow adequate water vapour transmission to avoidtrapping moisture within the wall.

56

Solid wall of brick or blockwork, usually with inside finish of plaster

The external face is often rendered or painted to prevent rain/moisture penetration

Outer leaf, normally�of brick

Partial cavity fill insulation. Some walls may have no insulation or may be fully filled

Inner leaf of brick or blockwork, usually with a plastered finish

Outer leaf, usually brick

Cavity

Plywood sheathing (with breather membrane)

Timber framing infilled with insulation

Plasterboard internal finish (with vapour membrane)

a) Solid walls

b) Cavity walls

c) Timber-framed walls


For new properties the choice of materials includingbricks, mortars and renders should be carefullyconsidered to limit water penetration during flooding.Generally denser materials will provide greater floodresistance.

The outer leaf of a timber-framed wall is normallyformed from masonry with or without a sand/cementrender finish. Other cladding types, such as tiles,timber, plastic and metal sheeting, can also be foundbut these are often above the first floor level. Floodingis unlikely to damage these types of cladding,although some timber cladding boards may need tobe replaced. All fixings should be corrosion resistantespecially where there is a risk of seawater flooding.

The inside face of external walls

To improve the flood resistance of internal wallsurfaces (assuming that floodwater will enter thebuilding), there are a number of measures that canbe taken depending on the type of wall and surfacefinish as follows.

Gypsum plasterSolid and cavity masonry walls normally have aninternal finish of plaster applied directly to the brickor blockwork. Gypsum based plaster on masonrywalls is likely to deteriorate following repeatedexposure to floodwater.

It is normal practice for gypsum plaster to beremoved from the wall face after floodwaters havesubsided to a level just above the flood tidemark. Thisis normally carried out regardless of the plaster’scondition to allow the underlying masonry to dry out.

Consideration may be given to replacing gypsumplasters with more flood resistant materials such as:

• An internal water-resistant render and lime basedplaster finish.

• Ceramic tiles: particularly in kitchen areas.

• Hydraulic lime coatings.

57

Consideration may be given

to replacing gypsum plasters

with more flood resistant

materials.


Any new water resistant lining should be installed toa height of 500mm above the maximum expectedflood level to prevent water being absorbed into theold lining above. For refurbishment works and newbuildings it may be more cost effective to install thelining to ceiling level.

Lime based plasterLime based plaster products have good waterresistance properties and once installed over a waterresistant render, such as sand/cement or proprietarysealant, should provide effective resistance toflooding provided such finishes are applied in fullaccordance with the manufacturer’s instructions.Following immersion in floodwater lime based plastersover a water resistant render should dry out quicklyand should not deteriorate even if subjected torepeated exposure to floodwater. The water-resistantrender beneath the plaster reduces water penetrationinto the underlying masonry, allowing the wall to dryout more quickly without the need to remove theplaster finish. Hence repair costs can be reduced.

Hydraulic limeHydraulic lime finishes with water resisting additivescan also provide effective flood resistance formasonry walls, both internally and externally. As withlime based plaster, hydraulic lime coatings have goodwater resistance properties and can allow walls to dryout without the need for replacement followingimmersion in floodwater.

Ceramic tilesCeramic tiles can also provide a water-resistantsurface and can reduce the volume of floodwaterpenetrating through to the masonry from the insideface of the wall. Tiled finishes should not need to bereplaced following exposure to flooding provided awater resistant grout, suitable for the wall surface, isused in accordance with the manufacturer’sinstructions. Tiles should be laid over a sand/cementrender to provide a flat wall surface. For floodprotection purposes, tiles should not be placed overgypsum based plaster.

58

Following immersion in

floodwater lime based

plasters over a water

resistant render should dry

out quickly and should not

deteriorate even if subjected

to repeated exposure to

floodwater.


It is essential that specialist advice is obtainedbefore any low permeability linings (such as thoselisted above) are applied, to ensure that moisture isnot trapped within the wall, otherwise problems ofdamp may occur.

Plasterboard (solid walls and cavity walls)Solid masonry walls and cavity walls may haveplasterboard finishes, often known as ‘drylining’.Plasterboard has low flood resistance and will almostcertainly need to be replaced following exposure tofloodwater. Existing plasterboard on solid masonrywalls can be replaced with a water resisting liner suchas a lime based plaster, ceramic tiles or hydraulic limecoating as discussed above. Where this is notpracticable plasterboard sheets can be placedhorizontally rather than vertically. In the event offuture flooding this can reduce the amount ofplasterboard exposed to water damage, reducing thecost and time of repairs.

Fixings should be of galvanised/stainless steel orcopper rather than mild steel materials which mayrust and cause staining of wall surfaces.

Internal finishes of timber-framed wallsThere are no practical options for improving the floodresistance of the internal face of a timber-framedwall. In most cases the plasterboard will need to beremoved to allow the timber frame to dry out andthe plasterboard sheets themselves will also normallysuffer damage if exposed to floodwater.

Replacing plasterboard sheets horizontally on atimber framed wall is unlikely to be practicable dueto the presence of the vapour control layer betweenthe timber frame and the plasterboard lining. Thevapour control layer prevents condensation fromforming within the centre of the wall, avoidingpossible decay of the timber frame. It is thereforeessential that the vapour control layer is repairedduring flood damage restoration works. Replacingplasterboard sheets horizontally would createproblems in providing an effective joint in thevapour control layer.

59

Fixings should be of

galvanised/stainless steel or

copper rather than mild

steel materials which may

rust and cause staining of

wall surfaces.


There is unlikely to be any benefit in replacingplasterboard with water resistant timber sheeting asthis would still need to be removed to allow thetimber frame to dry out thus, negating any potentialcost savings.

Insulation materials and cavities

Solid masonry walls Solid masonry walls in modern properties may havean external or internal layer of insulation.

Solid walls with plasterboard finishes may incorporatean internal layer of insulation between the masonryand plasterboard. Low absorption boards or semi-rigid self draining mineral wool batts to 500mmabove the expected flood level should be consideredrather than quilted insulation materials. Insulationbonded to plasterboard will usually need replacementif exposed to floodwater.

External insulation incorporating self-draining mineralfibre batts or boards or rigid plastic insulation is likelyto be only temporarily affected by flooding and willultimately dry out.

Cavity walls Even if measures are taken to improve the waterresistance of the outside face of the wall it is likelythat some floodwater will seep through to the cavity,particularly in the case of long duration floods.

After repeated exposure to floodwater the steel wallties between the internal and outer leaf of the wallmay begin to corrode, particularly in cases ofsaltwater flooding. Wall tie corrosion can often bedetected from signs of cracking within the mortarjoints. Should corrosion be identified the ties shouldbe replaced with stainless steel ties. Specialist advicefrom a qualified building surveyor will be required forthe inspection and replacement of wall ties.

60

Solid walls with plasterboard

finishes may incorporate an

internal layer of insulation

between the masonry and

plasterboard.


Stainless steel ties should be used in all new buildproperties at risk of flooding.

The thermal performance of some insulationmaterials may be reduced following saturation fromfloodwater, particularly lightweight blown-inmaterials. For existing properties such materials canbe replaced with closed cell insulation foam, which isnot water absorbent, but this can be a difficult andexpensive task. Specialist advice from cavity-fillinstallers should be obtained to establish whetherreplacement is necessary and to identify the optionsavailable.

Timber-framed walls Existing insulation within a timber-framed wall willtypically consist of highly absorbent mineral wool thatis susceptible to flood damage. Such materials willneed to be replaced after exposure to floodwater.Other more flood resistant insulation materials areavailable but it is unlikely that using such materialswould provide any cost benefit as they wouldnormally still need to be removed in order to allowthe timber frame to dry out.

Replacing damaged insulation with new mineral woolis likely to be the most cost effective option after thetimber frame has been allowed to dry out acceptingthat the material will need to be replaced shouldflooding re-occur.

Sheathing fitted on the outside of the timber frame(normally plywood or oriented strand board) providesadditional stability to the timber frame called rackingresistance.

Fibreboard sheathing may become weakened as aresult of flooding. If a structural assessment by aqualified engineer shows the racking resistance to beinadequate new WBP bonded plywood sheathingshould be added to the inside of the frame.

61

Existing insulation within a

timber-framed wall will

typically consist of highly

absorbent mineral wool that

is susceptible to flood

damage. Such materials will

need to be replaced after

exposure to floodwater.


The timber frame within the wall is unlikely to beadversely affected by flooding provided it dries outwithin a few weeks. The longer the timber remainswet the greater the risk of decay.

Steel Framed WallsThere are now a number of specialist steel framedwall systems available within the UK. Advice on whatmeasures can be taken to improve the floodresistance of these systems should be sought fromthe product supplier.

Internal walls

Masonry walls The flood resistance of internal masonry walls can beimproved by following the principles set out on page 57relating to external masonry walls (inside face).

Some partition walls in older properties may have lathand plaster linings. After exposure to floodwaterlinings of lath and plaster, in good condition, can dryout within a few weeks in a heated building.However, repeated flooding will almost certainlyresult in decay of the lining and the need forreplacement.

Stud wallsSome stud partition walls may be load bearing(supporting walls and floors above) so it is importantto seek professional advice before carrying outremedial works.

Stud walls, comprising of timber framing andplasterboard are vulnerable to damage from flooding.Consideration should be given to replacing untreatedsoftwood timber with water-resistant timber sections.Plasterboard sheets can be replaced with timberpanels, using WBP bonded plywood, but this isunlikely to provide a good finish for decorations.Alternatively, plasterboard can be replacedhorizontally thus reducing the amount ofplasterboard replacement should flooding re-occur.

62

The timber frame within the

wall is unlikely to be

adversely affected by

flooding provided it dries

out within a few weeks. The

longer the timber remains

wet the greater the risk of

decay.


Partitions in timber-framed buildingsIn timber framed houses some internal walls may beload bearing. No vapour control layer will be presentand hence plasterboard sheets could be replacedhorizontally rather than vertically.

Separating wallsWalls used to separate semidetached or terracedhomes are designed to provide an effective soundand fire barrier. Alterations to separating wallsshould not be made without prior approval froma Building Control inspector.

Masonry walls of brick or blockwork are likely to beof solid or cavity construction finished with plaster orplasterboard.

In timber framed houses the separating wall is alsolikely to be timber-framed. These walls are finishedwith extra layers of plasterboard and incorporatesound absorbent material (interference with thesound absorbent material may permanently impairsound insulation properties). There are no practicalmeasures that can be taken to improve the floodresistance of these walls.

63

In timber framed houses

some internal walls may be

load bearing. No vapour

control layer will be present

and hence plasterboard

sheets could be replaced

horizontally rather than

vertically.


Lucy and Anthony Rees took a calculated risk whenthey bought an attractive cottage that had beenflooded the previous autumn. The young coupleloved the house, weighed up the odds of it floodingagain – it had only been flooded once in the past 30years – and thought it was worth taking the chance.The next autumn it was flooded again, this time to adepth of 0.6 metres.

Anthony had just qualified as a building surveyor andafter the kitchen units and plaster had been strippedout, he set about researching what should be putback. The loss adjuster (who was busy with a mass ofother claims) gladly agreed to him writing thespecification for the repairs, and organising thecontractors to carry out the work. Of all the floodedhouses in the town, his was probably the first to bere-occupied.

He decided that the first thing was to avoid usinggypsum plaster, which had not withstood this floodor the one before, and rather to use a sand/cementrender with a lime-based rather than gypsum-basedskim coat.

Before these were applied, he decided to waterproofthe inside of the walls, using a sealant product usedfor basements, tunnels, and shower floors. In thisway only the plaster layer would need to be dried outbefore the house was re-occupied, not the entirethickness of the wall.

To maintain the tanking, the skirting boards havebeen glued to the wall rather than screwed and canbe quickly removed. He has also installed a sump foran electric pump, which he intended to use withflood doors as the first line of defence. Before theycould test the system, Anthony and Lucy have movedhouse – not because of the threat of flooding, butbecause of a change of job. The fact that they soldthe cottage at the asking price, within weeks of itbeing put on the market, must be partly due to theflood protection measures they put in place.

Source: Lucy and Anthony Rees

64

CaseStudyCS


Floors

There are three main floor types used withinresidential buildings and small business properties inthe UK, suspended timber floors, solid concrete floorsand suspended concrete floors.

Suspended timber floors

Timber joists and floorboards will normally dry outafter being immersed in floodwater without any longterm effects provided they have been treated with anappropriate preservative. Should joists need to bereplaced they can, subject to professional advice, besupported on hangers rather than being built intowalls. This can help to minimise the risk of futuredistortion following wetting and drying. Additionalstruts or battens can also be installed between joiststo reduce the risk of future distortion.

Flooring materialsChipboard flooring usually needs to be replacedfollowing exposure to floodwater and should bereplaced with appropriately treated floor boards orWBP plywood. Removable hatches should be installedto allow access to the sub floor void and to allow thevoid to dry out following flooding.

InsulationMany suspended timber floors in modern buildingshave mineral wool insulation between the timberjoists. This material has poor flood resistance and willneed to be replaced following exposure to floodwater.

Other more water resistant insulation materials areavailable, such as low absorption boards. Although itmay be possible to re-use this type of insulation afterexposure to floodwater it would be more expensiveto install than mineral wool, and would need to beremoved temporarily to allow the timber joists to dryout. The additional material and labour costs involvedare likely to outweigh any replacement cost savings.Hence replacing damaged floor insulation withtraditional mineral wool is likely to be the least costoption, accepting that this material will needreplacement should flooding return.

65

Ground level

Floorboard

concrete slab

Soil Level

Floor joists

F d tiFoundation

Airbrick

PeriscopeVentilator

DampProof Course

Suspended timber floor


Sub-floor void

After floodwaters have subsided water is likely to beretained below the suspended floor within the sub-floor void. The sub-floor void should be cleaned ofdebris to allow future floodwater to be quicklypumped away and to avoid moisture retention. In thecase of refurbishment works or new propertiesconsideration should be given to providing a fall to thesub-floor surface to a sump at an identified drainagepoint where a pump can be installed to evacuatemoderate seepage flow from future flood events.

For modern buildings the sub floor area is likely to becovered with 100mm of concrete or heavy-dutypolyethylene sheeting with concrete or sand blinding.Any damage to these linings as a result of floodingshould be repaired during the drying out period.

Solid concrete floors

Modern solid concrete floors with damp proofmembranes are generally regarded as the most floodresistant floor type as they can reduce the rate ofseepage into the building and are generally easier toclean and restore when compared to suspended floors.In particular solid floors do not have sub-floor voidswhich often require cleaning out following flooding.

However it should be noted that very few solid floorsin existing properties have effective connectionsbetween the damp proof membrane (dpm) and thedamp proof course (dpc) in the walls, so floodwateringress is likely to occur at the floor/wall joint. Fornew properties, or replacement floors, in areas at riskof flooding effective connections between the dpmand dpc should be provided.

Older properties with solid concrete floors, especiallythose built before the 1950s, have no dpm beneaththe concrete slab and will be less effective in reducingfloodwater ingress, particularly in areas of permeableground conditions and where the floor slabs arecracked.

66

Modern solid concrete floors

with damp proof membranes

are generally regarded as

the most flood resistant

floor type.


Although concrete floor slabs are unlikely to besignificantly damaged by flooding they can take along time to dry out depending on the location ofthe (dpm). Floors with the dpm between the surfacescreed and the concrete slab will dry out more quicklythan floors with the dpm below the concrete slab.

Floor materialsIn more modern buildings, solid floors also include alayer of insulation which can be located either aboveor below the concrete slab. Insulation for solidconcrete floors in areas of flood risk should take theform of rigid boards with low water absorption.

Some concrete floors have chipboard finishes abovethe concrete slab, sometimes supported on timberbattens. If exposed to floodwater it is likely that suchfinishes will require replacement. Considerationshould be given to replacing chipboard with screed(to a minimum thickness of 65mm), tiles or WBPbonded plywood.

Underfloor heating systems can be found in somesolid concrete floors, particularly in those constructedduring the 1970s. Such systems may be damaged byflooding and should be checked by a qualifiedelectrical engineer before re-use.

Suspended concrete floorsSuspended concrete floors are typically formed by in-situ or precast concrete beams with infill units oflightweight concrete or clay blocks. A damp proofmembrane of polyethylene directly above the floorunits is normally laid to prevent moisture from thesub-floor void reaching the floor surface. Insulation oflightweight blocks or moisture resistant material isoften laid between the separating layer and surfacescreed.

As with suspended timber floors floodwater is likelyto collect in the void beneath the floor. In the case ofrefurbishment works or new properties considerationshould be given to providing a fall to the sub-floorsurface to an identified drainage point.

67

Ground level

Screed

Concrete Slab

Soil

Damp proof membrane - 1950s onwards

F d tiFoundation

Compacted Hardcore

DampProof Course

Solid concrete floor


Chipboard boarding is sometimes found withsuspended concrete floors rather than a finishinglayer of screed. As discussed above under solidconcrete floors such finishes will nearly always needto be replaced following exposure to floodwater. Aconcrete screed of minimum thickness 65mm willprovide a more flood resistant surface and if properlyinstalled should not require replacement followingexposure to floodwater, provided access panels areprovided to gain access to the sub-floor void.

Concrete beams within suspended concrete floorscontain reinforcement that can corrode if there is ahigh chloride content within the floodwater. Duringrestoration of a property after flooding the conditionof the concrete beams should be inspected for signsof corrosion.

Replacement floors

In cases of repeated flooding consideration may begiven to replacing existing suspended floors with anew solid concrete floor. Solid concrete floors,provided they are properly designed to withstand thepressure of floodwater, can provide an effective sealto prevent water seeping up from the ground.Effective connections are however required betweenthe damp proof membrane beneath the concrete slaband the damp proof course in the walls. Solidconcrete floors generally suffer less damage thansuspended timber floors and are normally lessexpensive and faster to restore following exposure tofloodwater.

Radon and landfill gas barriers

In many parts of the country ground floors need tobe sealed to prevent naturally occurring radon gas, ormethane or carbon dioxide from landfill sites, fromseeping into the building though the ground. Forsolid concrete floors the radon barrier also serves asthe damp proof membrane beneath the concreteslab. For suspended timber floors polythenemembranes are installed below ground level.

68

Ground level

Screed

Soil levelSoil level

Void under floor

Concrete beamswith

block infillPeriscopeVentilator

F d tiFoundation

DampProof Course

Wall

Concrete block

Suspended concrete floor


In areas of high radon levels ventilation sumps aresometimes installed. Such sumps are likely to requiremaintenance following flooding.

When undertaking any measures to improve theflood resistance of ground floors it is importantnot to damage such gas barriers or sumps. If indoubt seek professional advice.

Basements

For existing properties with basements specialistadvice must always be obtained before undertakingany measures to prevent water ingress. Restrictingingress through internal or external tanking forexample may lead to an increase in hydrostaticpressure acting on the basement walls leading topossible structural damage.

Basement construction should usually be avoided fornew properties within flood risk areas.

69

For existing properties with

basements specialist advice

must always be obtained

before undertaking any

measures to prevent water

ingress.


Andrew Arrol is a conservation architect living inShrewsbury close to the River Severn. When he andhis wife Meg moved into their house in 1972, thetide mark from the 1947 flood was still visible on thewalls. When the floods of 1998 brought 75mm ofwater into their home, Andrew and Meg set aboutmaking it more flood-resistant. Using his professionalknowledge combined with a practical, commonsenseapproach, they have adapted their house to be asflood-resistant as possible without using materials orfinishes that look out of place.

They have chosen solid floors rather than suspendedtimber flooring, avoiding hidden spaces that canharbour moisture and be difficult to dry out. Thereare no fitted carpets on the ground floor. Electricitysockets, telephone points and electric and gas metershave been raised above likely flood levels enablingthem to remain comfortably upstairs during a floodevent. Temporary drain-stops are used in the sewersto prevent sewage being forced back up into thehouse by the rising floodwater. They also weightdown manhole covers to prevent them lifting, sealoverflow pipes, and cover ventilation grilles andairbricks before a flood. They use plywood floodboards on mastic bedding across the doors. Insteadof MDF or chipboard kitchen units, they havedesigned a shelving system from marine ply, strongenough to take the weight of the white goods,which can then be temporarily stored on top.

For the interior lining of the walls, they have workedon the principle of air gaps and moisture breaks. Forplaster they have used a hydraulic lime, applied tostainless steel mesh. The mesh is mounted ontanalised battens using stainless steel screws, and athin layer of plastic membrane separates the battensfrom the wall. The hydraulic lime contains an additivemaking it impermeable to water but permeable towater vapour. It has been finished with a compatiblepermeable paint. The plaster layer sheds the wateralmost immediately and the gap between the plasterand the brickwork means that air can circulate freely,speeding up the drying process. The rooms are

70

CaseStudyCS


habitable in a very short time and the brickwork candry out at its own pace.

The skirting boards have been made of treatedtimber, and have been painted all over so that theydon’t absorb water and warp. The skirtings are boxedout from the wall so that there is an air gap behindthem.

In 1998 the force of the rising water had actuallycracked the concrete floor slab in the hall. This wasrenewed leaving a small gap around the edges torelieve the pressure of the water. Polystyreneinsulation under the concrete was continued upround the edges to fill this space.

The precautions that Andrew and Meg have takenwere tested by 0.525m of water in the floods ofautumn 2000. The only damage sustained was acracked floor slab in the hall, and that has now beenrenewed in the same way as the dining room floorwhich survived unscathed. Thanks to timely warningsfrom the Environment Agency, and much hard workall the furniture was moved upstairs beforehand –Andrew and Meg advocate a policy of “one hundredpercent rescue”. In future they hope thatredecoration will be the only repair work necessaryafter a major flood.

The steps they have taken to improve the floodresistance of their house has significantly reduced thecost of flood damage repairs and restoration times.

Source: Andrew and Meg Arrol

71


Fittings and Building Services

Kitchens

CupboardsThe majority of kitchen storage units are formed fromchipboard and MDF with plastic coatings. Such unitswill almost always need to be replaced when exposedto floodwater. It is preferable to raise such units100mm to 150mm above floor level by means ofplastic legs to prevent damage during shallowflooding events.

Cupboard doors and worktops are also often madefrom chipboard or MDF and these will also usuallyrequire replacement if exposed to floodwater. Solidhardwood doors may dry out but warping ordiscolouration of the surface finish may still result inthe doors needing to be replaced. If sufficientwarning is provided cupboard doors may be removedin advance of floodwaters entering the property.

Water-resistant PVCu kitchen units that can becleaned and re-used following exposure tofloodwater are now available in the UK. Such systemsshould be considered when undertakingrefurbishment works or building new propertieswithin flood risk areas. It should be noted howeverthat such water-resistant units would often still needto be removed temporarily following flooding toallow the floors and walls to be cleaned and dried.

AppliancesSeparate hobs and built-in ovens are preferable tocombined free-standing cookers as these aremounted above floor level and may not be affectedby shallow flooding. Remember that all gas andelectrical appliances that have come into contact withfloodwater must be inspected by a qualified engineerbefore they are re-used.

Washing machines and fridge freezers usually need tostand on the floor due to their weight and should notbe permanently raised to provide protection against

72

Remember that all gas and

electrical appliances that

have come into contact with

floodwater must be

inspected by a qualified

engineer before they are

re-used.


floodwater, unless specialist design measures aretaken. It may be possible to empty and temporarilyraise freezers on low-level blocks provided there issufficient flood warning time.For properties at risk of flooding separate fridge andfreezer units should be considered rather thancombined fridge/freezers as they would be easier tolift in the event of flooding.

73


In April 2000 Mary and Arthur Lynch moved into acottage on the banks of the River Severn. They wereinformed by local residents and their surveyor’s HomeBuyer’s Report, that the house hadn’t been floodedeven in 1947, when river levels had been the highestin living memory.

However, six months later, in a flood that fellconsiderably short of the 1947 level, the Lynch’s had0.7metres of water in their house. They retreatedupstairs with supplies of bread and cheese and ginand tonic to sit out the flood.

When the river levels receded, their brand newkitchen, finished only weeks before, was completelyruined. The MDF panels had become soggy andswollen and the entire kitchen had to be ripped outand thrown away.

Rather than put back a second kitchen made of MDF,the kitchen fitter suggested that he should try andfind a more durable material. He has constructedstrong plastic base units that, are resistant to water,easy to clean and disinfect, and can be put back intoservice once the water has receded. The backs of thecabinets are designed so they can be removed, whichallows the wall behind to be cleaned and dried. Theclip-on plinths can be removed and stored in a dryplace before the flood, and this allows easy access tothe floor area for cleaning and drying afterwards. Thequick fit-and-release doors can be easily removed,and so don’t need to be waterproof, giving acomplete choice of materials.

The kitchen offers other solutions: the electric ovencan be disconnected, lifted out and placed on top ofthe work surface, and the units are also strongenough to support items such as the fridge andfreezer, which then can still be used.

Mary is delighted with the kitchen, as she has nointention of moving. “I would rather live by the riverand be flooded, than live without the river”, she says.

74

CaseStudyCS


Meanwhile the kitchen fitter is gathering other ideasfor coping with flooding, and has established a smallspecialist firm installing flood-resistant cabinets inkitchens and offices lying in the floodplain.Source: Mary and Arthur Lynch

Bathrooms

Toilets and hand basins are not normally affected byflooding. However, many plastic baths have integralchipboard bases to provide rigidity. These bases canoften become contaminated on exposure tofloodwater resulting in the need to replace the bathunit. Higher quality bath fittings should be consideredduring refurbishment works or for new buildproperties at risk of flooding.

Doors

There are a number of external and internal doortypes including timber, PVCu and aluminium.Generally solid doors and frames are less susceptibleto flood damage than hollow types which can fill upwith contaminated water during flooding which canbe difficult to drain.

Timber doors

Hollow timber doors, although less expensive thansolid timber, will often de-laminate on exposure tofloodwater and will usually need to be replaced. Solidtimber doors are likely to be only slightly affectedby flooding but some distortion often occurs andre-fitting is usually necessary. Such distortion canbe minimised by ensuring all faces of the timber,including the bottom face, are effectively sealed usingeither an oil-based or waterproof stain or paint.

Fire doors

Fire doors are often constructed with layers of fireresistant material that can become damaged ifexposed to floodwater. Fire doors that have beenimmersed in floodwater should always be replaced,together with the door frame seals.

75

Solid timber doors are likely

to be only slightly affected

by flooding but some

distortion often occurs and

re-fitting is usually necessary.


Windows

Timber windowsTimber window frames may distort followingexposure to floodwater and may need to be re-fitted.As with timber doors such distortion can beminimised by ensuring the timber is effectively sealedusing either an oil-based or waterproof stain.

Double-glazed aluminium and PVCu windowsand patio doorsModern double-glazed windows and patio doors arenormally made from hollow extruded aluminium orPVCu sections. These can fill up with floodwater andcan be difficult to drain.

For prolonged floods lasting more than a few hourswater can penetrate through the edge seal of doubleglazed units into the cavity between the glazing. Insuch cases the glazed units will require replacement.

Staircases

Solid timber staircases will generally only be slightlyaffected by flooding. However care should be takento ensure that the staircase has not become unstableand any loose treads should be replaced.

In some modern housing staircases are formed fromMDF and these may need to be re-fitted or replacedfollowing exposure to floodwater. Duringrefurbishment works and for new properties, theinstallation of solid timber staircases should beconsidered below the expected flood level.

Skirting boards

Skirting boards are normally formed from softwoodtimber or MDF.

Solid timber skirting boards should not be affected byfloodwater provided that all faces, including the backface and underside, are sealed with an oil-basedpaint or stain before fixing to the wall. Timberskirting boards will however normally need to betemporarily removed to allow the walls to dry out.

76

During refurbishment works

and for new properties, the

installation of solid timber

staircases should be

considered below the

expected flood level.


Non-treated timber boards will distort followingflooding and will usually need to be replaced.

Skirting boards formed from MDF are likely to requirereplacement if immersed in floodwater.

Floor coverings

For properties at risk of flooding fitted carpets shouldbe avoided where possible. Carpets will normallyneed to be replaced following immersion infloodwater although specialist cleaning services areavailable. Consider using loose fitting rugs that canbe moved and stored upstairs before flooding occurs.

For kitchens and bathrooms, the type of floorcovering will depend on the floor type. For solidconcrete floors, stone, concrete or ceramic floor tilesshould not normally be affected by flooding.However care should be taken to ensure that the tileresin or grout is sufficiently water resistant.

For suspended concrete and timber floors, permanentfloor tiles are not usually suitable as they would needto be removed following flooding to gain access tothe sub-floor void. Less expensive synthetic floorcovers should be considered such as lino etc althoughthese floor coverings will normally need to bereplaced following immersion in floodwater.

Wooden laminate flooring is also likely to be damagedby floodwater and will normally require replacement.

Wall coverings

Redecoration of the internal walls will almost alwaysbe required following flooding. Wallpapers willnormally peel away from the wall or become badlystained following immersion in floodwater and willneed to be replaced. Hence for properties at risk offlooding it is recommended that papered finishesshould be avoided.

Painted walls will normally also need to beredecorated following flooding but will be less

77

Carpets will normally need

to be replaced following

immersion in floodwater

although specialist cleaning

services are available.

Consider using loose fitting

rugs that can be moved and

stored upstairs before

flooding occurs.


expensive to refurbish than papered walls. The use oflow permeability lime-based paints rather than oilbased paints or emulsion can allow walls to dry outmore quickly following flooding.

Ceramic tiling may also be used as discussed aboveunder solid masonry walls (on page 58) but specialistadvice should be obtained to ensure that such lowpermeability finishes do not lead to problems ofdamp in the walls.

Electricity supply

Before floodwaters arrive the electricity supply shouldbe turned off at the consumer unit (fuse box).Following internal property flooding a qualifiedelectrician should be called to check the building’selectrical system (and any appliances that have beenimmersed) before it is re-connected.

Location of meter and consumer unit (fuse box)For many older properties both the electricity meterand consumer unit (fuse box) are located at low levelinside the house, often in the cupboard under thestairs. If there is sufficient space raising the meter andconsumer unit (fuse box) to a higher level above theexpected flood level could be considered subject toapproval by the local electricity supply company.

For modern houses the electricity meter is often locatedoutside the property in a box mounted on the externalwall. For new properties within flood risk areas locatingthe meter box and internal consumer unit above theexpected maximum flood level should be considered.

WiringModern electrical wiring is not normally affected byimmersion in floodwater. However for long durationfloods lasting several hours, water may penetrate theinsulation and in such cases the wiring may needreplacement. During refurbishment works, or whenbuilding new properties, moving the ground floor ringmain cables to first floor level could be consideredwith drop down cables to ground floor sockets.

78

For new properties within

flood risk areas locating the

meter box and internal

consumer unit above the

expected maximum flood

level should be considered.


It is also advisable to use plastic cable conduits ratherthan to plaster cables directly into the wall in order toreduce the cost of future rewiring should this berequired. However care must be taken to ensure thatcable conduits are installed to avoid low points thatcould collect water in the event of flooding.

Socket heightFor properties at risk of flooding raising the socketsto an appropriate height above flood levels could beconsidered. Although this could lead to savings inflood repair costs it should be noted that theappliance cables would become more visible insidethe room.

Gas supplyIn the event of flooding the gas supply should beturned off at the meter. Following immersion byfloodwater it is essential for safety reasons that theoperation of the gas system and individual gasappliances are inspected by a CORGI registeredengineer before the system is re-used.

During a flood, water and silt may find its way intogas systems affecting their safe operation. Theappliances may light and appear to be workingnormally but the flue or ventilation systems may havebeen adversely affected by the floodwater or partiallyfilled with water.

Gas meters may be affected by floodwater and it isworth considering raising meters above the expectedflood levels during refurbishment works or for newbuild properties. Provision should be made forpurging gas supply pipes through the installation ofappropriate drain points.

79

Following immersion by

floodwater it is essential for

safety reasons that the

operation of the gas system

and individual gas appliances

are inspected by a CORGI

registered engineer before

the system is re-used.


Central heating systems

BoilersGas and oil fired boilers and associated pumps andcontrols should preferably be installed above themaximum expected flood level. Fittings that havebeen immersed by floodwater should be inspected bya qualified engineer before re-use and may need tobe replaced.

PipeworkHessian or fibre insulation to pipes below suspendedfloors can reduce in thickness following soakingleading to a reduction in thermal effectiveness. Pipeinsulation below the expected flood level shouldpreferably be replaced with closed cell insulation.

When installing new heating systems, pipeworkroutes should be easily accessible to allow pipes to bemaintained and washed down following flooding.Central heating pipework and radiators are unlikelyto suffer damage from flooding, unless corrosionoccurs as a result of several weeks of contact withwater containing salts. This can happen if, forexample, pipes are inaccessible within concrete floors.

Storage HeatersElectrical storage heaters will normally requirereplacement following immersion in floodwater.

Drainage

Non-return valvesFlooding can create blockages in drains and sewerswhich can lead to the backflow of sewage intoproperties through low level drain gulleys, toilets, andwashing machine outlets. Backflow through drains isparticularly likely where floodwater is prevented fromentering the property using temporary barriers andwhere the external flooding depth outside is abovethe internal level of the drain entry points.

Such flooding can be effectively controlled byinstalling non-return valves, often called anti-floodingdevices, within the private sewer of a propertyupstream of the public sewerage system. These

80

When installing new heating

systems, pipework routes

should be easily accessible

to allow pipes to be

maintained and washed

down following flooding.


devices are typically between 0.5 to 1 metre in lengthand are installed in-line within an inspection chamberto allow access for maintenance. They are designedfor installation within gravity sewers or drains andnormally use flap gates to prevent backflow. Furtherdetails are provided by the CIRIA publication ‘Low-cost options for prevention of flooding from sewers’.

It must be remembered that once an anti-floodingdevice has closed to prevent backflow, it effectivelydisconnects the property from the public seweragesystem. Appliances within the property, such astoilets, and washing machines cannot be used untilthe flooding has subsided and the device re-opens,otherwise the property may be flooded by its owndischarges.

It is important to remember that anti-flooding devicesrequire careful installation and must be regularlymaintained. Maintenance depends on the type ofdevice fitted, but is normally required every sixmonths.

Private sewage systems

Flooding of a private sewage system can create aback-up of sewage into the property and lack ofsanitation. Damaged septic tanks, cesspools, or smallpackage sewage systems should be inspected by aqualified engineer before the drainage system isre-used.

Water supply

Water meters and pipework will not normally beaffected by flooding but some pipework insulationmaterials may become damaged. This should bereplaced with flood resistant closed cell materialbelow the expected flooding level.

Telephone and cable services

Following flooding some problems have been foundwith communications wiring due to the collection offloodwater within cable conduits. Suppliers of the

81

It is important to remember

that anti-flooding devices

require careful installation

and must be regularly

maintained. Maintenance

depends on the type of

device fitted, but is normally

required every six months.


relevant services should be consulted on suitableinstallation methods in areas liable to flooding.Where possible incoming telephone lines, andinternal control boxes, should be raised above theexpected flood levels.

82

Summary

The aim of this guide has been to bring together bestavailable information on the measures that can betaken to minimise the impact of flooding on existingdomestic and small business properties and toprovide guidance on how the most appropriateoptions can be selected.

Advice and guidance is also provided to developersand local authorities involved in new buildconstruction and the renovation of existing propertiesat risk of flooding in support of the Government’snew planning policy on development and flood risk(PPG25).

The table below illustrates some of the main impactsof flooding that can be reduced by effective pre-planning and implementation of appropriate floodprotection measures detailed within this guide. Thekey message is that a combination of both pre-planning and flood protection measures will providethe greatest benefit.

83

Summary6

Howpreventativemeasures canreduce costsand stress

Loss of personal

belongings

Temporary loss of

home/business

Clean-up costs

Restoration costs

Replacement and

purchase costs

Preparing aFlood Plan

Measures tokeep the waterout

Measures toimprove theinternal floodresistance ofthe building

Combination ofmeasures

✓✓ ✓✓ - ✓✓✓

✓✓ ✓✓ ✓✓ ✓✓✓

✓✓ ✓✓ ✓✓ ✓✓✓✓✓ ✓✓ ✓✓ ✓✓✓

✓✓ ✓✓ ✓✓ ✓✓✓

✓✓Some reduction in

flood impact

✓✓✓Significant reduction

in flood impact


For existing householders and small business ownersat risk of flooding the adoption of measuresdiscussed within this guide should help to reduce thefear and stress of flooding, reduce the cost of flooddamage repairs and enable individuals and businessesto return to normality more quickly.The guidance is the first attempt to collate suchinformation in one source document and willcontinue to be improved and updated as newinformation becomes available and feedback isreceived. In particular, work is now underway toprovide national performance standards againstwhich flood protection products can be tested, andto improve knowledge on the flood resistance ofbuilding materials.

84

The guidance is the first

attempt to collate such

information in one source

document and will continue

to be improved and updated

as new information

becomes available and

feedback is received.

Summary

85

Identify the sourceof the flood risk.

Flood risk – thetrue cost of flooding

Assess the cost ofrepairing flood damageand replacing belongingsif the property wasflooded to the maximumflood depth.

Assess the indirect costs ofbeing flooded including thestress of losing belongings,organising repairs, and livingin temporary accommodation.

Qu

anti

fy t

he

likel

iho

od

Qu

anti

fy t

he

con

seq

uen

ceA

sses

s th

e O

pti

on

s to

red

uce

ris

kIm

ple

men

t &

Rev

iew

Action plan

How often doesflooding occur?

Maximum depthof past floods at the

property.

Damage to propertyand belongings.

Donothing

Plan ahead toreduce flood

damage

Take measuresto keep the waterout (dry-proofing)

Take measuresto improve internal

flood resistance(wet-proofing)

The social costs offlooding.

Assess combinations of options

Decide on an option or combination of options

Put the options into practice

Review the options after flooding

What is the cost of carrying out the measure?What is the reduction in flood damage?

What is the saving?


86

Further Reading

General reading

• Floodline information pack contains basic advice onthe Environment Agency’s flood warning serviceand what to do before, during and after a flood(Available from Floodline).

• Information guides; Flood Products – Using FloodProtection Products – A Guide for Homeowners,After a Flood – how to restore your home,Drainage Limitation – how to make your homemore flood resistant and Flooding in Gardens(Available from Floodline).

• Lessons Learned Autumn 2000 Floods (EnvironmentAgency).

• Webpages on Repair and restoration of buildingsfollowing floods. Includes advice sheets aimed atthe householder on how to improve the overallflood resistance of their home. (CIRIA –www.ciria.org/flooding)

Technical reading

• DETR (2001) Planning Policy Guidance Note 25:Development and Flood Risk (DTLR, London).

• Learning to Live with Rivers, Institution of CivilEngineers (November 2001).

• Flooding: A Partnering Approach to ProtectingPeople, ABI (November 2001).

• Assessment of costs and effectiveness on futureclaims of installing flood damage resistantmeasures. ABI May 2003. ISBN 1-903-193 24-9

• Floods and Historic Buildings: Technical advisorynote (in preparation), English Heritage.

• Flooding and Historic Buildings: Proceedings of thejoint conference of English Heritage andShrewsbury and Atcham Council held inShrewsbury 27th March 2001 (in preparation),English Heritage.

87

Further Reading7


• Temporary and Demountable Flood Protection –Interim Guidance on Use. Environment Agency, R&D Publication 130, 2002.

• Reducing the Impacts of flooding – ExtemporaryMeasures. Special Publication SP15S (CIRIA) 2001.

• DETR (2001) The Government’s Response to theSecond Report in Session 2000-01 of theEnvironment, Transport and Regional AffairsCommittee: Development on, or Affecting, theFloodplain (HMSO, London).

• Environment Agency (2000) An EnvironmentalVision: The Environment Agency’s contribution tosustainable development (Environment Agency).

• Scottish Office (1996) Design Guidance on FloodDamage to Dwellings (HMSO).

• Federal Emergency Management Agency (1995)Engineering Principles and Practices for RetrofittingFlood-prone Residential Structures IndependentStudy Course (USA).

• Building Research Establishment (1997) RepairingFlood Damage Part 1: Immediate Action. GoodRepair Guide 11 (CRC, Watford).

• Building Research Establishment (1997) RepairingFlood Damage Part 2: Ground Floor and Basements.BRE Good Repair Guide 11 (CRC, Watford).

• Building Research Establishment (1997) RepairingFlood Damage Part 3: Foundations and Walls. GoodRepair Guide 11 (CRC, Watford).

• Building Research Establishment (1997) RepairingFlood Damage Part 4: Services, Secondary Elements,Finishes, Fittings. Good Repair Guide 11(CRC, Watford).

Useful websites

• Association of British Insurers (ABI):www.abi.org.uk

• British Damage Management Association (BDMA):www.bdma.org.uk

88

Further Reading

• Building Research Establishment (BRE):www.bre.com; www.ask.bre.com; andwww.brebookshop.com

• National Flood Forum (NFF):www.floodforum.org.uk

• Flood Protection Association:www.floodprotectionassociation.org

• Construction Industry Research and InformationService (CIRIA):www.ciria.org.uk/flooding

• Office of the Deputy Prime Ministerwww.odpm.gov.uk

• English Heritage:www.english-heritage.org.uk

• Environment Agency:www.environment-agency.gov.uk/floodresearchfor electronic copies of Environment Agency R&Doutputs.

• Middlesex University’s Flood Hazard ResearchCentre:www.fhrc.mdx.ac.uk

• Scottish Executive:www.scotland.gsi.gov.uk

89


90

Environment Agency Guidance

What to do before, during and after aflood

The Environment Agency recommends that thefollowing steps are taken to prepare for possibleflooding and offers advice on what to do whenwarnings are issued and how to cope in theaftermath. For more information call the Agency’s24 hour Floodline on 0845 988 1188 or check theirwebsite (www.environment-agency.gov.uk/floodline).

91

Environment Agency Guidance8


Be prepared

• Keep a list of useful numbers to hand: for exampleyour local council, the emergency services, yourinsurance company and Floodline – 0845 988 1188.

• Have a few sandbags or floorboards prepared toblock doorways and airbricks.

• Make up a flood kit, including a torch, blankets,waterproof clothing, wellingtons, a portable radio,first aid kit, rubber gloves and key personaldocuments. Keep it upstairs, if possible.

• Talk about possible flooding with your family orthose you live with. Consider writing a flood plan,and store these notes with your flood kit.

• Make sure you know where to turn off your gasand electricity. If you’re not sure, ask the personwho checks your meter when they next visit. Markthe tap or switch with a sticker to help youremember.

• What about your pets? Where will you move themto if a flood is on the way?

• Think about your car. Where could you move it toin the event of a flood warning?

• Get into the habit of storing valuable orsentimental personal belongings upstairs or in ahigh place downstairs.

• Think about medication. In the event of a flood,you’ll still need to take it.

• Contact your insurance company to check you haveadequate flood cover.

92


Ideas for a family action plan

✓ Do know how to contact each other. Your familycould be anywhere when a flood happens.

✓ Do find out where your family would be evacuatedto. Make sure you all know where that is. Floodsmay force you to leave your home.

✓ Do put the emergency numbers in a safe place.Prepare a flood kit which can be kept in a safeplace.

✓ Do know where to turn off your power supplies.Do you have a torch handy in case it’s dark?

✓ Do make sure you understand what the floodwarning service for your area is.

✓ Do find out whether your area has flooded before.Look in the library or ask neighbours whathappened and how they coped.

✓ Do tell a friend or neighbour about your plan. Youmay need their help if there’s a flood, or they mayneed yours.

✓ Do read through the Agency fact sheet ‘Are youprepared for a flood?’.

✓ Do think if there is someone who will need yourhelp.

✗ Don’t wait for a flood to find out whether yourplan works. Try it now.

93


Coping after a flood – the first steps:

✓ Do open your doors and windows to ventilate yourhome. It takes a brick about an inch a month todry out. Do take care to ensure your house issecure. Remember to unblock airbricks anddoorways.

✓ Do wash your hands with disinfectant if you comeinto contact with the water directly. Watch out forany broken glass or nails while you’re clearing up.

✓ Do check in Yellow Pages under Flood Damage forsuppliers of cleaning materials or equipment to dryout your property.

✓ Do wash taps and run them for a few minutesbefore use. Mains tap water should not becontaminated but check with your local watercompany if you’re concerned.

✗ Don’t attempt to operate any damaged electricalgoods until they have been checked by a certifiedelectrical engineer. Floodwater conducts electricity.

✗ Don’t attempt to operate any gas appliances untila certified gas engineer has checked them. Becareful with naked flames. Gas pockets, oil andother contaminants can build up in and aroundfloodwater.

✗ Don’t eat food that has come into contact with thewater – floodwater contains sewage and othercontaminants.

✗ Don’t walk through fast flowing water in thehome or outside – floodwater can be fast moving.Just six inches of water can knock you off yourfeet. Be careful of holes and dips when movingaround. Use a stick to gauge depth.

94


Claiming on your insurance

✓ Do telephone your insurance company’s 24 houremergency helpline as soon as possible. They willbe able to provide information on dealing withyour claim, and assistance in getting things back tonormal.

✓ Do commission immediate emergency pumpingand repair work to protect the property fromfurther damage. This can be undertaken withoutinsurer approval (remember to get receipts).

✓ Do get advice where detailed, lengthy repairs areneeded. Your insurer or loss adjuster can giveadvice on reputable contractors and tradesmen.Be aware of bogus tradesmen.

✓ Do check with your insurer if you have to moveinto alternative accommodation as the cost isnormally covered under a household policy.

✓ Do make sure your insurance company knowswhere to contact you if you have to move out ofyour home.

✓ Do make notes to assist your insurer in dealingwith your claim, including:

• time of flood warning.

• time the flood waters entered your home.

• the maximum depth of the flood (this can bemarked on a wall).

• how long the flood water was in your home.

• presence of any contaminants (oil, sewage, etc).

• what damage was done to building (walls,floors, etc) and contents (carpets, sofas,electrical goods). If possible, take pictures ofwhat was damaged.

95


Restoring your property – first steps

✓ Do check the external walls and roof of your homefor structural damage to make sure it is safe to enter.If necessary, contact your local authority for advice.

✓ Do leave all the internal and external doors andwindows open in the house where possible. Thiswill help walls and floors to dry out.

✓ Do try to keep an inventory of correspondenceafter the flood (e.g. letters to local authority,builders, your insurer, loss adjuster)

✗ Don’t attempt to dry out paper or photographs.Place them in a plastic bag and if possible placethem in the fridge.

✗ Don’t panic if you feel you can’t cope. Your localCitizens Advice Bureau and other organisationsmay be able to help if you feel under pressure –check their number in the phone book.

✗ Don’t think it can’t happen again. Restock yoursupplies.

96

Documents

Preparing for floods: interim guidance for improving the ... · ODPM Publications Centre PO Box 236 Wetherby West Yorkshire LS23 7NB Tel: 0870 1226 236 Fax: 0870 1226 237 Textphone: