Chilterns Area of Outstanding Natural Beauty · note.Adherence to the guidelines does not mean that development proposals will necessarily be approved because other planning policies

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Chilterns Roofing Materials Supplementary Technical Note -Adopted Version

Acknowledgements

2 ChilternsRoofingMaterials

This Technical Note has been published by theChilterns Conservation Board which would like toexpress its thanks to Dr. James Moir who hasresearched and written this Note.

Thanks must also go to members of the AdvisoryGroup who have given extensive help and advicevoluntarily.

Thanks also to Colin White, ChilternsConservation Board Planning Officer for his helpin organising the Group and input into revisionsto the text.

Particular thanks are also due to the following:

Tim Amsden (SMT Conservation)MartinAndrew (Wycombe District Council)George Crutcher (Formerly of South BedfordshireDistrict Council)Nick Doggett (CGMS Consulting)Roger Evans (Former Buckinghamshire HistoricBuildings Officer)Jimmy Goodchild (Goodchild Roofing)Simon Jones (Simon Jones, Architect)Glyn Kuhn (Polar Design)Jim Matthews (HG Matthews)Catherine Murray (Chiltern District Council)Ian Pritchett (IJP Building Conservation Ltd.)Derek Rogers (Architect)

All photographs are by Dr. James Moir unlessotherwise acknowledged. All drawings are bySimon Jones and Glyn Kuhn.

The Chilterns Conservation Board wishes toacknowledge the generous grant aid madeavailable by the following organisations towardsthe cost of producing this Note:

The Countryside Agency (now Natural England)South East England Development Agency,Chiltern District Council,South Oxfordshire District Council,Dacorum Borough Council,South Bedfordshire District Council,Wycombe District Council,Bovingdon Brickworks Ltd,Dunton Brothers andH G Matthews.

Chilterns Buildings Design Guide - Chilterns RoofingMaterials, Supplementary Technical Note

Published March 2007

No part of this publication may be reproduced ortransmitted in any form without the prior permission ofthe Chilterns Conservation Board.

ISBN 0-9545242-4-1

c

Cottages (Penn)

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ForewordThe Chilterns Conservation Board recognises theimportance of good design in the built heritage ofthe Chilterns Area of Outstanding Natural Beauty(AONB).We published the Chilterns BuildingsDesign Guide in 1999 and have supplemented itwith Technical Notes on Brick and Flint.

The intention of these publications is to makeproperty owners, builders and architects aware ofthe need to protect the distinctive character of ourbuildings and settlements.

The Board wishes to encourage the use ofappropriate materials for roofs and has, therefore,prepared this Technical Note.

The previous notes have encouraged the use ofsustainable local resources. This one follows thesame pattern in promoting the use of tiles, as well

3

as other appropriate materials, in newdevelopments in the Chilterns. The methods oftile use have changed little over the centuries.They came in a variety of shapes sizes andcolours and have been used on every type ofbuilding. Tiles are, once again, being made in theChilterns in the traditional manner for the firsttime for 50 years.

We only need to see a line of traditionalbuildings in a Chilterns town or village torecognise the harmony of brick and flint wallscrowned with tiles of local manufacture.

Sir John JohnsonChairman, Chilterns Conservation BoardMarch 2007

Chapter 1Introduction 4Chapter 2Background 8Evolution of the Roof 9Historical Manufacture and Use of Tiles 12Other Roofing Materials 14

Chapter 3Designing the Roof 16An Inspirational Inheritance 16Preliminaries 16Massing and Geometry 19Roof and Building Performance 21Material Choice and Combinations 22Material Selection and Specification 26

Chapter 4Detailing the Roof 29Openings 29Eaves, Verges and Ridges 30Valleys, Hips and Abutments 34Rainwater Goods 37Chimneys, Flues and Vent Pipes 38

Chapter 5Sourcing and Selection 39Selecting a Contractor 39Obtaining RoofingMaterials 39

Chapter 6Repairs, Alterations andExtensions 40Repairs and Maintenance 40Conversions 43Extensions and Alterations 44

Chapter 7Designing for Sustainability 45

Contents

School Complex (Ibstone)

ChilternsRoofingMaterials

Glossary 47Bibliography 49Further Advice 49

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Introduction

4

Chapter 1

1.1 Roofing materials have a major influence uponthe built environment of the Chilterns and thecharacter of its individual buildings. The firstimpression approaching a village or town is oftenthe view of its roofs seen from a distance. Thehilly terrain allows views over buildings andcreates roofscapes which would not otherwise beseen. Roofs should, therefore, be designed to thehighest standards and clad in attractive materialswhich make a positive contribution to thecharacter of the area.

1.2 Many roof types and styles can be found inthe Chilterns, and thatch, slate, corrugated iron,lead and wooden shingles cover a proportion ofthe region’s older buildings. However, plain claytiles are universally predominant and their texturalrichness and distinctive dark orange or red colourleave a lasting visual impression. Such tiles havean unbroken history since the early medievalperiod and this long usage has invested theregion’s buildings with a particularly strong andconsistent character and identity. That identityhas nevertheless been eroded by the appearanceof new roofing materials and forms; some have aplace but others are used in inappropriatecontexts.

1.3 The Objectives of the guidance are to:

� Raise awareness of the quality of thetraditional built character of the ChilternsAONB by highlighting the importance oflocal styles and forms of roofing

� Create respect for the historical diversity ofroofs in the region

� Re-establish traditional character in areas ofthe AONB where it has been damaged oreroded

� Protect the distinctive character of the builtenvironment by encouraging good repairpractices

� Foster an interest in reviving traditionalmaterials and skills in the region so as toencourage a more sustainable approach toroofing

� Promote the appropriate use of roofingmaterials in new developments so as tocreate respect for the traditional builtcharacter of theAONB

� Encourage roofing of the highest standardto inspire high quality design in newdevelopments

Chapter 1 : Introduction

Clay roofs characterise this village (Little Missenden) (Image GeoPerspectives.com)c

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1.4 Much of the Chiltern Hills is designated anArea of Outstanding Natural Beauty (AONB). TheChilterns Conservation Board is responsible forconserving and enhancing the natural beauty ofthe AONB, increasing the understanding andenjoyment of its special qualities, and fosteringthe economic and social well-being of localcommunities, within theAONB. It may offerassistance to local authorities with the aim ofensuring their policies and practices are co-ordinated and consistent with guidance that hasbeen adopted.

1.5 To this end, the Chilterns Buildings DesignGuide was published in 1999 to provideguidance on how to achieve high qualitydesign in new developments. The Guideprovides a framework for protecting andenhancing the identity of the traditional builtcharacter of the Chilterns, which has beensteadily eroded by the use of standardiseddesigns and non-local materials. This series ofTechnical Notes is intended to supplement theChilterns Building Design Guide by providingadditional guidance on the appropriate use ofmaterials.(visitwww.chilternsaonb.org the ChilternsAONB website for details of other TechnicalNotes.)

1.6 All new building work, including extensionsand conversions, will require careful considerationof the roof design and its covering; repairs toexisting buildings may also involve changing theroofing material or improving its performance. Thisnote aims to provide guidance in these areas butis not a comprehensive historical and designstatement. It illustrates a potential for excellence,diversity and flexibility in new design whilst stillrespecting the distinctive qualities of the area.

1.7 This guidance is intended to be used by allinvolved in the development process: owners;

architects; designers; developers; builders;planning authorities; parish councils and anyorganisation or individual with an interest in thebuilt environment of the ChilternsAONB.


Aylesbury

DunstableLuton

Chesham

Marlow

WallingfordBeaconsfield

PrincesRisborough

Tring

River Thames

Henley-on-Thames

Wendover

River Thames

M1

M40

M25

HighWycombe

Amersham

Berkhamsted

Goring

HemelHempstead

St Albans

Hitchin

Reading

Map 1The Chilterns Area ofOutstanding NaturalBeauty




1.8 The note is a material planning considerationand will contribute to decision-making onplanning applications. Local planning authoritieswill be invited to adopt it as a materialconsideration so as to ensure consistency acrossthe 15 local planning authorities within which theAONB lies. If adopted, the planning authoritieswill expect all relevant planning applications in theAONB to demonstrate how these guidelines havebeen taken into account. Contact theConservation Board to check on the status of thenote. Adherence to the guidelines does not meanthat development proposals will necessarily beapproved because other planning policies willapply. Specific design and planning guidance isalso likely to apply to buildings that have been

listed or are situated in conservation areas. Thelocal planning authority should be contacted fordetails.

1.9 This note was the subject of publicconsultation prior to adoption. The views ofconsultees were taken into account and in somecases changes were made. A copy of all therepresentations made during the consultationperiod and the Conservation Board’s response isavailable from the ChilternsAONB office.

Sustainability

1.10 Roofs play a key role in enhancing the builtenvironment of the Chilterns. The use and re-useof traditional materials will help retain the existingidentity of the Chilterns and create attractive newdevelopments of lasting character. Many artificialand natural but non-indigenous materials areimported into the region.Apart from their visualimpact, they are likely to be costly in energy toproduce and to transport; their life expectancymay also be far less than a traditional roofingproduct. With increasing concern for theenvironment, development should aim to usematerials which produce lasting buildings.Materials that can be recycled and repaired ratherthan thrown away or replaced should beencouraged. However, they must be technically

6

appropriate for new work, should always becarefully sourced and should not involve materialsbeing stolen from a historic building.

1.11Clay is a natural material; roof tiles aredurable, natural, sustainable products thatimprove with age and weathering.Anumber ofsmall firms in the south of England produce hand-made clay-peg tiles which blend well with localexamples; their use supports craft skills andeconomies of scale in production. Clay tiles arestill competitive in terms of costs, are perhaps theeasiest and most economical roofing material interms of fixing, and have a life of sixty years ormore with little need for care or maintenance.

Streetscape (Nettlebed)Concrete tiles and flat roofs – alien materials and formin the Chilterns (Hemel Hempstead)



7

1.12 Until the Second World War, tiles wereproduced in conjunction with locally-made bricks;and it is this which may once again provide aspringboard for a renewal of the craft. Re-establishing local tile production offers one of thekey conservation opportunities in the region forthe 21st c. Brick manufacturers in the Chilterns areideally placed to pioneer the re-introduction oftilemaking given the relative ease with which theskills and machinery required to mould brickspecials can be adapted and transferred to tilemaking. There is a real possibility that roof tileswill once again be produced commercially in theChilterns.

1.13 The Government is committed to thereduction of greenhouse gases as a result of theKyotoAccord on Climate Change. In terms of roofdesign, the impact is to require more insulation onthe envelope, limit heat loss from pipes and ducts,and assist in providing more energy efficientheating, cooling and ventilation systems. Roofdesign and performance therefore have a majorrole to play in determining the building’s overallenergy performance. The combination of covering,underlay and insulation are controlled by BuildingRegulations; within these constraints, roofs canbecome effective solar heaters; rainwaterharvesting systems can capture water run-off; and

Chiltern District Council Foyer, demonstration modelshowing local, sustainable, building materials(Amersham) (Photo by C. White)

Reviving the Chilterns tile makingindustry (H. G. Matthews)


PictureofChilternDCfoyerexhibit(CWwilltakeifnecessary)

New construction using prototypeChiltern tiles

roof surfaces can positively support and enrichthe ecology of the surrounding environment.

1.14 The convergence of conservation policies (topreserve historic buildings by encouragingsympathetic renovations and extensions) andsustainability agendas (to stimulate local indus-tries to keep transport costs low) has created a‘niche’ opportunity to revive the Chilterntilemaking industry.

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2.4 In the Chilterns, littleelaboration and decoration isfound in tile roofs. Pitches arerelatively steep; eaves tend to befinished with plain half-roundguttering; and gables rather than

hips produce straight verges without recourse tobargeboards.

2.5 Other roofing materials have been used in thepast. Research into insurance records demonstratethat in 1801, roughly two-thirds of all roofs weretiled, one third thatched (see Fig 1). Slate was justbeginning to make an appearance in the area,particularly in the market towns and on largeestates such as Ashridge due to the evolvingcanal network. Some early industrial buildingswere experimenting with corrugated iron and eventarred paper. Grander buildings often had metalroofs of lead or copper.

2.6 The market for native Chiltern roofingmaterials continued to be eroded throughout the19thc. and 20thc. by imports (both from elsewhere inthis country and abroad). The Second World Warappears to have placed a final seal on tileproduction within the region. Tilemakers wererecorded at: Ley Hill up to 1928; at Chalfont StPeter to 1935; at Hedgerley up to 1936, and the

8 Chapter 2 : Background

BackgroundChapter 2

2.1 No stone suitable for producing slates isavailable in the Chilterns. In many areas of theregion, deposits of clay-with-flints overlayingthe chalk bed rock have for centuries yieldedclay suitable for both brickmaking and tilemaking – this opportunity for dual output ishistorically why peg tiles were the mostcommonly used roofing material in the Chilterns.

2.2 Differences in the clay inevitably producesubtle variations across the Chilterns in tilecolour and texture, but these tend not to be aspronounced as for the region’s bricks.Differences in hand moulding, fuel, firing time,temperature and position within the kiln can alsoall affect the tile’s appearance.

2.3 Most tiles are rectangular in shape, butvariously shaped tiles laid in a variety ofpatterns may be encountered, sometimespromoted by large estates aiming to achieve a

distinctive design. Profiledtiles are found in the northeast of the region, spillingover from the pantiled areasof EastAnglia.

Shaped and patternedtiling (Little Kimble)

Map 2 Distribution of Tiles in England

plain tiles

pantiles

Steep pitched plain tiled roof(nr. West Wycombe)



9Chapter 2 : Background

Allied Brick and Tile Works in Copperkins Lane,Amersham struggled on until c.1949.Subsequently supplies came from tileworks on themargins of the region such as at Reading butthese too gradually dried up in the final decadesof the 20thc. Although a reasonably healthy hand-made tile making industry survives in England,this is based in the South East and Midlands,using clays that cannot exactly match the colourand texture of native Chiltern tiles.

(Source: Sample policies from Sun Life Insurance Records, Guildhall Library, London.)

Fig 1: Chiltern Roofing Materials, 1801

Dwellings Ancillary Domestic Farm Buildings Industrial

Numbers ofbuildings

600

500

400

300

200

100

0

Roofscapes have evolved over time (Hemel Hempstead)

2.8As box-framing emerged, timber roofs evolvedto resist the lateral tensions which otherwisewould force the walls apart. To prevent sagging,collars were introduced to link pairs or couples ofrafters across the building. These might be furtherstiffened with struts and braces. An alternativemethod of preventing lateral thrust was to tie thewall-plates together across the building with tie-beams. On these, the principal rafters sat. Tie-beams were used at intervals, effectively dividingthe building up into bays. To prevent the trussesor coupled rafters from racking, collar and ridgepurlins and windbraces were introduced. Earlybuildings tended to have ‘in-line plans’ but largermedieval buildings had cross-wings, resulting inthe creation of valleys. As two storey buildingsbecame more common from the 15thc., chimneys

Evolution of the Roof

2.7 The purpose of a roof is toprotect the living space fromrain. Early roof designs werebased on cruck frames, wherethe weight of the roof wastransferred directly to theground. Examples of crucks areencountered in the Chilternsbut are rare after the end of the15thc.

Tile

Thatch

Other



Early chimneys (West Wycombe)

Principal roof trusses (Fingest) Parapet walls (Hemel Hempstead)

Dated hopper (Hemel Hempstead)


appeared at gable ends, on side walls of cross-wings, or axially set on ridges. When compared tothatch, tiles caused rainwater to run off morequickly. Eaves overhangs steadily reduced asrainwater disposal was increasingly controlledthrough the introduction of gutters anddownpipes.

2.9 Roofs with principal trusses were predominantin the Chilterns between the 15thc. and 19thc.,

although roof members tended to become moreslender over time. This whole period wasundoubtedly the heyday for the clay tile, as thatchincreasingly fell out of use (particularly in urbanareas due to the risk of fire) or became relegated toancillary buildings. Particularly in towns, roofsbecame concealed behind parapet walls. Cast irongutters and downpipes became more universal.

2.10 In the 19thc., new technologies inspiredresearch into new roof forms. Timber trusses stillpredominated but increasingly they were bolted –the king post roof being a particularly commonform; later still the strutted purlin roof emerged.Wider spans were achieved with tensioned metaltrusses. Shallower pitches emerged in response toimported materials – at first slate (penetrating the

area with thedevelopment ofcanals and thenrailways), thensheet metals.The latter alsoallowedcurvilinear roofsto emerge.

Decorated ridge tiles became a more commonsight, particularly in towns. Gables, bayprojections, porches and complicated roof profileschallenged roofers to produce cut roofs to a highstandard. Thatch enjoyed a limited revival in the



11Chapter 2 : Background

late 19thc. and early 20thc. in conjunction with theArts and Crafts movement and the emigration ofcity dwellers in search of their rural idylls.

2.11 In the 20thc., roof structures evolved in twodirections. On the one hand, lighter roof trusseswere developed and post WWII pitched roofswere built with economic, lightweight, wooden,premanufactured roof trusses designed forshallower pitches – 35 to 40° depending on roofspan. From c.1964 the ‘W’ shaped trussed rafterroof using metal connector plates to join thetimbers emerged as the main form of roofconstruction. These allowed pitches to drop aslow as 22 – 30°, and by the early 1970s some roofswere down to 15° for up to 12 metre spans. But asroofs became flatter – or even flat - somestructures had to be reinforced to take the heaviermaterials being developed to make them watertight

2.13 Ancillary aspects of roofs have also changeddramatically. Chimneys and stacks have beenreplaced by metal flues or disappeared altogether.Pressures on space have caused dormers andskylights to sprout on roofs everywhere, breakingup uninterrupted planes. Requirements forventilation have tended to push eaves overhangsoutwards, although increasingly it can bediscreetly incorporated in roof slopes and ridges.

Arts and Crafts thatch (Penn)

– concrete tiles, asphalt, felts, and so on. Theoverloading of older roofs designed for lightermaterials was also an unfortunate spin-off.

2.12 Whereas in the 19thc. traditional roofcoverings could be accommodated on most roofs,the development of truss construction andmaterials in the 20thc. have limited some of thecontexts in which they would be appropriate orindeed perform at all. The development of glass,plastics, and lightweight materials has allowedspectacular new roof forms to be engineered.Nevertheless, clay tiles have responded tochanges in pitch and design remarkably well. Theyhave in fact benefited in recent years from areaction to low-pitched, trussed rafter roofs -these have been abandoned in favour of steeperpitches to meet space and design requirements bykeeping building mass and rooflines down andsqueezing more living room out of roof spaces.

Light roof trusses (Berkhamsted)

Example of poorly designed steep pitched roof withrooms squeezed into roofspace (Flamstead) Poorly designed modern roof



HistoricalManufactureandUse of Tiles

Early tiles (173 High St., Berkhamsted)

Tilemaking and brickmaking – a decorative tiled roofadjacent to bottle kiln (Nettlebed)

Paw-print in tile (ChilternOpen Air Museum)


2.14 The word ‘tegula’ or tile was used to describeseveral clay products including bricks and paviorsas well as roofing tiles.

2.15Older tiles are difficult to date, but tile-makingin the Chilterns is known to date back to the 13thc.and 14thc; tile kilns excavated at Ley Hill may infact predate the medieval revival of brick. In the13thc., the price for roof tiles averaged at threeshillings per thousand. At Penn and Tylers Green,a floor tile industry flourished between 1340-1390.See article by Miles Green in ‘Records of Bucks’Volume45, page 152 (2005).

2.16 The plain tile is so-called because itdescribes the ‘plane’ as opposed to variousprofiled tiles that were used. From an early datevarious urban authorities in particular attempted

to counter the danger of thatch fires by legislatingfor the use of tiles. Tiling battens had to be moreclosely and uniformly spaced as a result.

2.17 Apart from fire-resistance, the spread of tilessteadily produced a more uniform and more long-lasting roof covering. The size has changed littlesince the time of Edward IV when it was requiredthat a plain tile should be 10˚” long by 6˘” wide(most clay tiles today are 10˚” by 6˚” or 265 x165mm).

2.18 Bricks and tiles were generally manufacturedtogether. Both tiles and bricks were normally madefrom local clay, which was usually dug by hand inthe winter from pits using a clay spade. Havingbeen broken down by the frosts, the clay was thenwetted and mixed to a dough-like consistency.Each individual tile was made by hand; the claywas pressed by hand into moulds which had beendusted with sand. The tiles were then allowed todry on stackable coved racks (to give the requiredcurve) and then burnt in a clamp or kiln made atthe building site.

2.19 From 1784 onwards the price of tiles wasaffected by the Brick Tax to defray the cost of theAmerican War of Independence. Plain tilesattracted a duty of 3s.(15p.) and ridge tiles 8s(40p.) per 1,000. In 1833 (when the tax on tiles wasremoved) 42 million tiles were subject to the levy.

2.20 Traditionally, plain tiles were hung from laths.Each tile had two holes formed near its head. Pegsmade of oak or Baltic pine were pushed throughone or sometimes two of the holes and werehooked over the laths made of riven oak orchestnut which were nailed or sometimes peggedto the rafters. In plaintile roofs the position ofthe hole varied; theshape of the peg varied;the thickness andcontour of the lathvaried and the raftersvaried in size.



Chapter 2 : Background 13

2.21 Whatever the uniformity ofsize in the tiles, the resulting roofwas far from uniform in surface andappearance. To aid water run-off,the tiles were curved in length andhad a varying curve in width. Thiscross-camber helped direct waterrunning off one tile to the middle ofthe tile below. It also created biggerspaces between the tiles, avoidingany capillary paths and allowingproper ventilation. Cross-camberalso meant that the bottom edge of each tile wassupported on two points, not on a continuousedge which might be far from straight. The tilesthus had a more stable ‘sit’. The 1945 BritishStandard specified only a longitudinal camber.

Earlymachine-madetiles werecompletely flat,suffering muchfrost damage as aresult.

2.22 Following apatent granted in1836, the practicedeveloped ofincluding one ortwo nibs at thehead of each tile in

order to hang the tiles frommachine-sawn laths. Only certaincourses of tiles at the eaves and atlevels up the roof were nailed intothe laths. However, nibbed tiles didnot come into general use until latein the 19thc.

2.23Normally tiles were bedded insome material which would help toexclude draughts and make the roofresistant to the danger of driven

snow, a potential threat even to the steeply-pitched tiled roofs of the Chilterns. The normalbedding used in this region was straw (or hay);and this can still occasionally be found on some

surviving roofs. 17thc. accounts refer to mossbeing used in the Hughenden Valley.

2.24 During the 18thc. and early 19thc., fishscaleand other variations in shape were sometimesused – Bourne End, for example, has a particularconcentration. Subtle banding andpatterning effects were also created usingdifferent coloured tiles.

2.25 Tiles have occasionally been usedto clad walls in the Chilterns as well asroofs; it is a more common practice in thesouth-east of England. It is found onsome Edwardian – mainly Arts and Crafts- houses. Good examples are found

Cambered roof tiles

Nibbed tiles (173 High St.,Berkhamsted)

Tiles bedded in straw. Note also the wooden pegs(Fingest)

Tile-clad walls (Berkhamsted)

Decorative clay-tiled 19thc. roof (Flaunden)




around Goring, Whitchurch and Medmenham. Itbecame more widespread in the post-war era, oftenas a means of concealing block construction andprotecting leaky walls.

2.26 Tile-making machines, though invented inthe 19thc., appear to have largely by-passed theChilterns. However, machine-made tiles,particularly those made from the Etruria marl clays,allowed mass-produced brands such as‘Rosemary,’ ‘Acme,’ ‘Dreadnought’and ‘Broseley’to make inroads into the region. The Victoriantaste for elaborate mixtures of architectural stylesand materials also meant that free use was made oftiles in a greater variety of colour and shape. TheHoffman kiln had been developed in the 19thc. andwas the favoured method of firing tiles up to thetime production ceased. Other processes alsoevolved - machinery was used to crush, roll andfilter the clay and drying rooms were built tospeed up the process of reducing moisturecontent before firing. But by and large,mechanisation had little impact on the Chiltern tile-manufacturers, an obvious contributory factor toproduction declining in the 20thc.

OtherRoofingMaterials

Timber2.27 There is littlefirm evidence forthe use ofshingles in theChilterns excepton a few ‘superior’buildings. Oaklogs were cleftwith a froe; pegswere made tohang the shinglesfrom the roofingbattens. Becauseof their weightthey areparticularly suitedto very steep pitches – and thus are encounteredoccasionally on spires.

Thatch2.28 Research has indicated that a small numberof medieval thatched buildings survive with anoriginal base layer of thatch - this has becomeblackened by being exposed to smoke from anopen hall fire percolating up into the roofspace.No examples in the Chilterns have yet beenlocated, although a number survive in the Vale ofAylesbury. Insurance records demonstrate that in

1801, thatch was particularly common on smallerrural buildings such as cottages, farm buildings,outhouses and rural industrial buildings. Themajority of these roofs have since disappeared orbeen re-covered with another material. It is highlylikely that some of these lowly buildings weremaintained by farm labourers rather than masterthatchers, and base layers may again provideimportant clues as to idiosyncratic thatchingtechniques.

2.29 The majority of surviving examples howeverhave been thatched using long straw. Eaves wereliggered and ridges were plain. (For furtherinformation see English Heritage guidance note‘Thatch and Thatching’.)

Shingled roof (Hemel Hempstead)

Thatch (Wormsley)



Chapter 2 : Background 15

Slate2.30 Improved transport links, especially canalsand railways, brought slate mainly from Wales,particularly the great Penrhyn quarry at Bethesdain North Wales. In the 20thc., other markets openedup and Spanish and Chinese slates have allappeared on local roofs.

Slate (Kensworth)

Metal2.31 Grander buildings often had metal roofs ofimported lead or copper. (See English Heritage’sTechnical Handbook:Vol.4: Metals.) Some earlyindustrial buildings experimented with corrugatediron, which gradually covered over and eventuallyreplaced many of the humbler thatched roofs inthe region.

Glass2.32 Large span glass roofs developed from the1790’s and were mainly associated withgreenhouses, conservatories, orangeries andother garden structures. Conservatories fell out offavour during the early half of the 20thc., butreturned with a vengeance in the second half,unfortunately often using alternative Upvcproducts.

20th c. introductions2.33 New materials such as asbestos tiles becameparticularly prominent on the straggling ribbondevelopment to many Chiltern villages thatmushroomed in the interwar period. Flat roofsbecame common, particularly for extensions,favouring the spread of bitumen based productssuch as felts and asphalt. Concrete tiles madecomparatively little inroads into the Chilternsoutside the towns. Similarly, plastic and profiledmetal roof coverings have had little impact on theAONB except where light industry has beenLead (Nettlebed)

Corrugated iron (Henton Chapel, Chiltern Open AirMuseum)

allowed; associated roofing products such asfascias, verges and bargeboards, are, bycomparison, inappropriately conspicuous. Glazingtechnology also rapidly advanced, allowing amore inspired range of glass roof applications.



16

An InspirationalInheritance

3.1 The typical Chiltern roof has evolved inresponse to a subtle blend of environmentalfactors – a gentle inland climate which allowssmall and relatively light tiles to be placed on,rather than pinned to, the roof and which permitsverges and eaves to remain largely exposed ratherthan having to be shielded by coped gables andtall parapets; a broadly consistent geology whichproduces clay peg-tiles and associatedaccessories of a red/orange colour across theregion, together with the bricks which blend soharmoniously with the tiled roof coverings; all on

Characteristic traditional tiled roof under threat(Prestwood)

a human scale which has left roofs largelyuncluttered by complex detailing and over-elaborate ornamentation. The resulting subtle mixof shapes and materials contrast with theconsistency and machine-like quality of manymodern roofing products.

3.2 Many traditional roofs survive in theChilterns. Their shape, form and detailing shouldact as a template to inspire roofing of the highestquality, fit for its present day purpose. Eachproject will have its unique characteristics but alltoo often designers ignore this inheritance and failto ensure new roofs blend in with the existingenvironment. The essential features to create abalanced design are:

Preliminaries

a. Building type, usage and context

3.3 What is the function of the building and is itfit for its purpose? If new, is the buildingresidential, industrial, commercial, or is it anancillary/secondary building? Will it need to blendinto an existing group of buildings or can itsisolated position be exploited to advantage? Ifextending a building, consider how best tointegrate new and old roofs. If the current roof isfailing, the survey should identify the repairsrequired and a methodology to ensure they are

Chapter 3 Designing the Roof

Tiling in progress (Hemel Hempstead)

carried out with due regard to the survivinghistoric fabric.

b. Primary material choice

3.4 Decide what roofing material fits best with thecontext of the project. Should it be combined withother roofing materials? Consider also theimmediate built environment – what roofingmaterial has been used most extensively in thearea. In most areas of the Chilterns, this will beclay tiles and they should be specified whereverpossible. When infilling, matching the materialsalready present will normally be required.

Chapter 3 : Designing the Roof



17

3.5 With peg tiles, uniformity comes in size anddepth of lap. Variety comes in individual shape(where they are handmade), and in colour andtexture both bold (in variations in surface) as wellas fine (in the sandy texture of each tile). Detailedvariations in colour from mix and firing and in theway light catches the expanse of a tiled roof addfurther subtlety to the finished effect. Clay tilesare also versatile - they can follow ridge or hip,they can be laced, swept or turned around valleys.

3.6 If considering other coverings, bear in mindthat artificial materials may not be designed to lastas long as clay peg tiles and will not weather inthe same attractive way.

c. Planning and legal restrictions

3.7 Planning applications now require design andaccess statements as a matter of course for mostapplications in the AONB (see ‘Design and accessstatements – How to write, read and use them’,CABE, 2006). At an early stage in the designprocess contact should be made with the LocalPlanning Authority for advice regardingdevelopment and change of use, or theConservation Officer if an existing building islisted or situated in a Conservation Area. ThePlanning Officer for the Chilterns ConservationBoard may be contacted for advice, and theguidance in this Technical Note should be applied

to the project.Article 4 Directions may be in place,requiring planning permission for specific minordevelopments involving changes to a roof (whichotherwise may not need permission).

3.8 Any planned roofing works must consider therelevant legislation relating to wildlife. There is anobligation under the Wildlife and Countryside Actto consult Natural England about any buildingwork which might affect bats or their roosts.Guidance is available by contacting local batgroups, the Bat Conservation Trust(www.bats.org.uk) or your local Natural Englandoffice (www.naturalengland.org.uk), or byreference to Bats in Houses (see Bibliography).Roofs are also important nesting areas for swifts,and allowances should be made for them inconnection with any new roofing work. Seewww.concernforswifts.com for information andfurther detailed advice about nest holes and nestboxes and their location.

d. Building Control

3.9 The Building Regulations can have a majorimpact on design parameters, addressingstructural, health and safety and energy issues.Local authorities should deal sympathetically withproposals for repair and conversion of historicbuildings. The requirements of ApprovedDocument L could seriously erode historic

Tiles are versatile enough to adaptto many different roof forms (WestWycombe)

character and a more relaxed approach canbe taken in connection with listedbuildings, conservation areas andscheduled monuments. Please checkApproved Document L and contact yourlocal Conservation Officer and approvedBuilding Control Officer for further advice.

e. Site restrictions and potential

3.10 Consider the site carefully, as this willaffect both the aesthetic outcome and theperformance of the roof.

3.11 From an aesthetic point of view,should the same pitch be maintained for allelevations? Do not overcrowd a crampedsite with an overbearing roof.

3.12 Positioning the building correctly mayhelp to mitigate some of the conditionswhich the roof may be exposed to such asdriving rain, wind, shading from solarintensity etc. The desirability of havingtrees in close proximity to the roof shouldbe carefully considered. Ease ofmaintenance will also be affected.

3.13 The Building Regulations 1991approved Document B stipulate thatcertain roof coverings cannot be placed




18

nearer to site boundaries than indicated (strictinterpretation of this has, for example, preventednew-build thatch within 12m of a boundary) andcertain buildings may also need to be separated.

f. Client requirements

3.14 Carefully consider the owner’s or client’spreferences, who may be seeking distinguishedarchitecture or sustainable solutions in harmonywith other existing buildings. Ensure the client isfully briefed regarding the design opportunitiesrelating to roofing.

g. Capital resources

3.15Cost implications will influence the choice ofroofing material. The following table summarisesthe new-build cost per m2 for a range of roofcoverings.

The table should be treated as a general guideonly. Reclaimed materials may be twice asexpensive as new products. The client shouldalso be made aware of the life cycle costs asopposed to just the build cost. This will dependon factors such as typical life expectancy, scrapvalue and annual maintenance costs. Quoted lifecycle costs may pitch the life expectancy of tilestoo low – tiled roofs in the Chilterns tend to bewell protected from extremes and have beenknown to last twice as long as the 35 years usedin life cycle costing models. It is rare for anythingless than 40% of tiles stripped from an old roof tobe re-usable; the proportion in many cases willbe much higher. A thorough maintenancestrategy, if conscientiously applied, will alsoensure the roof’s life is prolonged beyondnormal expectations. It should also be stressedthat a clay roof ‘adds value’ which will exceedthe marginal increment to the overall cost ofconstruction that may be associated with the useof clay tiles.


Cost of covering(£/m2)

Pitched roofsClay peg tiles (hand made) 67Clay peg tiles (machine made) 45Natural slates (Welsh) 70Natural slate (Spanish) 55Man made slates 52Clay pantiles ( hand made) 45Thatch 95Concrete interlocking tiles 25Concrete plain 46Stainless steel sheet 60Lead sheet 91Zinc sheet 56Copper sheet 61Aluminium 48

Flat roofsSingle ply 54Sources:Davis, Langdon and Everest, Copper in Architectureand www.homebuilding.co.uk (2002)

DesignChecklist� Do design the roof using materials and to a

scale appropriate to the function of thebuilding and its context

� Do obtain all necessary permissions



19Chapter 3 : Designing the Roof

Massing andGeometry

3.16Roofs can ‘make or break’ a building. Roofsthat are too bulky can overwhelm not only thebuilding itself but also destroy an otherwisebalanced street scene.

3.17 The geometry of roofs has tended to becomemore complex, increasing the potential for defectsoccurring given that the roof will have moreintersecting planes.

The roof is over-dominant in this low-walled building

The roof configurations and tile-cladding to thisdevelopment do not draw on local precedents

3.18 Careful consideration of the roof geometrycan result in better interior ventilation and internaldaylight gain.

Mansard (Fingest)

Tiles laid at a very low pitch (Cadmore End)

Contrasting pitches for slate and tile (Hemel Hempstead)

3.19 Pitched roofs can span large spaces withoutimposing on the interior space available. In theChilterns, relatively steep pitches are common –only in the 19thc. did these flatten out as slate wasimported into the region. Traditionally plain claytiles were laid at 42.5° or 47.5° and this practiceshould be continued as a roof looksproportionally ‘right’ at such pitches, rather thanthe ubiquitous and inaccurate 40° or 45°. Whileclay plain tilesconforming to thedimensionaltolerances given inEN 1304 can be laidon rafter pitchesdown to a minimum

of 35°, as a general rule not less than 40° isrecommended. Mansard roofs, with much steeperpitches on the lower slope, are occasionallyencountered in the Chilterns. Most are of slate,although occasional tiled examples are seen.Where the lower half of the roof is of a shallowerpitch, the eaves may appear to be “swept”. Flatroofs (actually with slopes up to 10°) only becamecommon in the 20thc. The British Standard code ofpractice for flat roofs BS 6229 covers designissues. Only specialist contractors trained in theinstallation of the roof specified should be used.



20

Massing andGeometry Checklist� Do research techniques and styles in the

immediate area� Do respect the relatively steep pitches of

traditional Chiltern roofs

� Don’t create bulky roofs out of proportion tothe rest of the building envelope


3.20 Clay tileshave been usedsuccessfully tocover very largeexpanses of roof.Wider spans willcreate moreproblems as theweight increases.On smaller areas

of roof, larger tiles may look clumsy and out ofscale.

3.21 Roofs in the Chilterns generally terminate in agable or, less commonly, in a hip. Half-hips,‘gablets’ etc. are only very rarely encountered.The small size of the standard plain tile, however,lends itself to being adapted where necessary tothese more unusual complex roof details.

The incorporation of half hips in Chiltern roof designscan rarely be justified, particularly in conjunction withslender trussed roofs (Great Kingshill)

Gablets or ‘Norfolk hips’ are, as this name implies, nota traditional feature in the Chilterns (Chinnor)

The extension does not tie in with the existing roof shape

Extensive areas of tilingneed not create amonotonous effect(Bisham Abbey)

Combined gable and hip (Bledlow)

Secondary roofs to lower extensions, porches etc.usually work best when they echo the shape andform of the principal roof.

Chimney offset tiled with plain bedded verge to blend inwith main roof



21

c) snow and ice. Dry, wind blown snow canpenetrate tiny gaps in roof coverings, particularlywhere irregular handmade tiles have been used.d) aircraft vortices. These may need to be takenaccount of given that Luton and Heathrowflightpaths affect the Chilterns. Contact BRE forfurther advice.e) high humidity and temperatures. Roofs need tobe able to withstand movement caused byseasonal heat differences.f) excessive solar gain and ultraviolet light.Climate change is subjecting roofs to more extremeexternal conditions and solar radiation isincreasing in intensity.

Structure3.23 The most common form of roof for smalldwellings is the double cut roof with struttedpurlins supporting the rafters. ‘Fink and fan’trussed rafters or ‘attic trusses’ are alternatives.Steel structure roofs consisting of Zed purlinscarrying trays over which thermal insulation is laidhave also become available.

Barriers3.24 The provision of fire-breaks both within andbetween buildings and the need to seal elementsof the roof should be attended to. Fire can alsospread between tiling battens and these too mustbe sealed. Loft conversions in particular willinvoke additional elements of the Regulations.

Service installations, particularly electric cablesand ceiling spotlights should not be positionedclose to inflammable roof materials.

3.25 The roof is a key element in the maintenanceof appropriate internal environments bycontrolling heat loss, and all materials of a roof,and even the spaces between layers of materials,contribute to the building’s thermal performance.The interplay of high humidity, vapourpermeability and dampness in roofs is complex.When altering historic buildings, or in modernroofs, the control of condensation is vital and thisinvolves the correct use of ventilation, vapour


Roof andBuildingPerformance

3.22 Roofs have to cope with years of exposure,and many will not be maintained properly, if at all.The roof must be resistant to:a) driving rain. The south-east in particular isprone to short spells of high intensity rain.b) wind. Gales and gusts can particularly affectpitched lightweight roofs, and additional fixings orfixing centres should be used around the perimeterzone of the roof. On the lee side of a building thewind can create a suction on the tiles and thevacuum effect can be significantly higher adjacentto the perimeters. Calculations may affect thespecification for fixing tiles. Unequal pitch(asymmetrical) dual pitch roofs present problemsin calculating wind loads, and specialist adviceshould be sought

Fire-damaged steel sheeted roof. A cavity break atmid-point prevented the fire spreading to the right sideof the roof. (Hemel Hempstead)

Sheeps wool insulationbeing applied betweenrafters (Henley)

Felted roof (Bury)



22

tends to favour the adoption of this form of roofdesign. Adequate air paths in the batten cavitiesand insulation thickness should be incorporatedso as to maintain a simple roof profile. This in turnshould prevent perimeter detailing such as eavesand verges from becoming too bulky or ‘fussy’.The design challenge is to maintain simple,traditional roof profiles that can accommodate newrequirements for energy efficiency and ventilationwithout appearing cluttered.

PerformanceChecklist� Do ensure full compatibility between roof

coverings, barriers and structure� Do ensure all expected conditions are catered

for� Do design for sensible, safe maintenance

Material Choice andCombinations

3.28 Plain tile and brickwork go together inbeing essentially the same material with thesame basic method of manufacture and similardegrees of uniformity, variety and versatility.Specific information on tiles appears in thefollowing section.

3.29Atraditional Chiltern farmstead mightexhibit a hierarchy of roof coverings with peg-tiles on the main farmhouse roof, slates onsome farm buildings and thatch on others.Similarly, buildings which have developedorganically over time may have a range ofroofing materials – often in a similar hierarchy -peg-tiles on the main roof, slate for lowerpitched Victorian extensions, flat roofs for more


Ventilation tiles (near Stokenchurch)

Tile and thatch (Lewknor)

barriers, vapour permeable membranes andinsulation. (See BRE Thermal insulation:avoiding risks).

3.26 The position of the roof insulation will affectthe method of ventilation. The majority of domesticpitched roofs in the Chilterns will have been con-structed as ‘cold’ roofs, with the insulation at ceil-ing height. Where an impermeable underlay is used,ventilation should be provided into the roof space.If a vapour permeable underlay is used, adequate airmovement between the underlay and the tiles canbe provided by fixing a 25mm counterbatten overthe rafters. To avoid condensation, further ventila-tion can be introduced by slashing the felt betweenthe top 4 battens at ridge level on both slopes.

3.27 ‘Warm’ roofs have the insulation placed atrafter level. The pressure to utilize loft spaces



23

recent kitchen extensions etc. Careful combinationof various materials can considerably enrich theaesthetic appeal, but allowances must be made foradjacent roofs to move and for special flashingsetc. at the interface.

3.30 By their regular nature, usually lower roofpitches and generally subtle colour variation andtexture, slates are suited to creating a more formaland refined impression. Most roofs using naturalslates of United Kingdom origin should last atleast 100 years. British slate supplies today comefrom Wales, Cornwall and the Lake District. Theslate most commonly encountered in the Chilterns,particularly in mid and later 19thc. buildings islikely to have come from North Wales. This slate isthin and is riven relatively smooth. It can be cutaccurately giving a consistent shape and size. Thecolour ranges from dark grey through to distinctpurplish hues to paler silver grey and what iscommonly known as blue-grey. When wet theseslates have a distinctive shine. Welsh slate is laidin regular spaced courses. Some Westmorlandgreen slates may be encountered, laid indiminishing courses and usually on high qualitywork. Imported natural slate is now available fromSpain, SouthAmerica and increasingly China. Inappearance, these may be hard to differentiatefrom home produced varieties but they may beless finely riven (and therefore heavier) and have a

rough textured surface. A type appropriate to thebuilding and its setting should be chosen - seeBRE The building slates of the British Isles. Someimported slates may not pass BS 680 tests. SomeChinese slates have a tendency to discolour andturn ‘bald’ after fixing. Some Spanish slate haspyrites, which usually sparkles when new, buteventually rusts away, damaging and staining theslate. Avariety of artificial fibre/cement slates isalso now available. They can be of a similarthickness to natural slate and some haveinterlocking devices allowing a pitch as low as 15°.The more expensive or premium products will havea high natural slate content, a textured surface anda riven edge. But even the best tend to have a tooregular and monotonous appearance. The cheaperones have a bland, shiny look when new, but soonlose their pigmentation. They will crack if the nailsare driven in too far, and the bottom corners curlup if the disc rivet inserted at the foot of the slateis turned down too tightly.

3.31 It is usually recommended to lay slates to aminimum pitch of 25°. A roof of best Welsh slateswill weigh about 25kg/m2. In limited cases, it maybe appropriate to use diminishing courses, whilesmaller roofs may use smaller slates to maintaingood proportions. Slates may be head or centrenailed. All natural slates should have their ‘grain;’running parallel to their length for maximumdurability. The modern practice of fixing slateswith clips looks very unsightly and should beavoided. Traditionally slates come in a variety of‘standard’ sizes from305 x 205mm (‘smalls)through to Countesses (510 x 1205mm);Duchesses (610 x 255mm); and Empresses (610 x355mm). The slate most widely available is as longas twice its width, the size most frequentlyencountered in the Chilterns is referred to as 20x10(508 x 254mm). Spanish slate tends to be 250 x500mm and generally cannot be fitted to a roofbattened out at 9" gauge. The shallower the pitchthe larger the slate needed. Ridge tiles for slate aremostly 18" long and are most commonly angleridges, sometimes roll-top, but seldom “capped”,


Imported Spanish slate (Hemel Hempstead)

Well executed slate roof(Nettlebed)



24

and either red, blue or black. Alternatively, and onlower pitched roofs in particular, lead rolls mightbe used. On some Victorian or Edwardianbuildings, more elaborate patterned clay ridge tilesmay be appropriate over slates. Valleys may beformed by a Code 4 or 5 lead or zinc gutter lining.Sloping edge abutments and junctions on roofswith parapets or chimney stacks or changes inroof pitch (as for example in mansard roofs)should always be detailed with lead flashings(Code 4, 5 or 6) and not cement fillets.

3.32 Less than 5% of buildings in the AONB arethatched. The majority are to be found in thearable areas at either end of the chalk inBedfordshire and Oxfordshire and on the westernside towards the Vale. The performance of thatchdepends on a complex set of factors such as thesiting of the building, roof shape, quality of

material and workmanship etc. Long straw, asopposed to combed wheat reed or water reed, isthe ‘traditional’ form of thatch encountered in theChilterns. It can ‘flow’ over roofing structures,allowing great flexibility in ‘sculptural’ forms.Ridges were also of straw, laid ‘flush’ and plain inappearance. However, water reed was alsoimported into the area from c. 1920 to achieve amore ‘precise’, vernacular appearance on Arts andCrafts buildings; these inevitably would requiremore elaborate ridges in straw or sedge. Thatchedroofs usually have a generous overhang at theeaves without conventional gutters. No newbuilding of more than 1500m3 can have a thatchroof unless it can satisfy the relevant fire test.Figures for the longevity of thatch roofs should allbe treated with caution. Long straw should behollow stemmed, winter grown wheat, at least 30inches long, with the stems as little bruised as


Slate roof with lead rolls (Chiltern Open Air Museum)

Drawing straw for long straw thatching (Chiltern OpenAir Museum)

Thatched Cottage (Chilterns Buildings Design Awards2005)

possible and clean of foreign material. Long strawis yealmed – drawn into units – on the groundbefore being laid on the roof to a minimum depthof 380mm (15 in), commensurate with the pitchangle of the main roof. Coppice materials shouldbe specified for fixings.

3.33 Other roofs only rarely encountered in theChilterns include:� Profiled tiles – pantiles are orange/red incolour with a shallow ‘S’ shape profile and laid in aregular, wavy grid (unlike the staggered courses ofplain tiles) and generally laid at a relatively lowpitch (30° to 40°), providing a comparativelylightweight roof structure. Verges are oftenfinished with bargeboards. Ridges are traditionallya third, half round, hogsback or saddleback ridgetiles.



25

� Shingles - mainly confined to timberstructures and ecclesiastical buildings, and oftenof cedar, although oak is the tradidional andpreferred material. Shingles are relativelylightweight and should have a life of around 50years. Shingles are normally relatively long inrelation to their width: of the order of 300-600mm x100-325 mm. Thicker oak shingles need to be laidat a pitch of not less than 45º, though cedar

shingles may be laid at a pitch of 30º.Bargeboarded verges are preferred. Ridges areusually formed from standard shingles laidhorizontally to single lap, close butted at the ridge.Flammability of shingles may impose particularBuilding Regulation requirements. Cedar shinglesare usually treated with a preservative.

� Metal roofs, for which refer to theappropriate Trade Associations. Most metal roofsare laid to comparatively low pitches. Metal rooffinishes tend to have a very long life. All metalswill absorb oxygen and tarnish unless a protectivelacquer is regularly applied. Guidance for designand installation can be obtained from BS 5427-1,the Metal Cladding and Roofing ManufacturersAssociation and the National Federation ofRoofing Contractors. Main standards for lead areBS 1178 and BS 6915. Thicknesses of lead sheetare mainly in the range Code 4 to Code 8; Code 5should provide adequate durability for mostsituations. Sheet copper and zinc tend to be laidas fully supported roof coverings. Copper, themain standards for which are contained in BS CP143: Part 12 and for the material itself, BS 2870,weathers over the years to a blue-green, and thepatina forms a protective coating. Zinc usuallyforms a grey coloured carbonate when exposed tothe atmosphere, whichaffords protection tothe bare metal. Themain standards for zincare BSCP 143: Part 5and BS EN 988. TypeAis used for normalroofing and type B forflashings. Material andmanufacturingrequirements for self-


Profiled tiled roof (BledlowManor)

Roof constructed with tegulae appropriate to thisRoman site and Museum (Verulamium)

Shingles (Berkhamsted)

Metal seamed roof(Hemel Hempstead)



aesthetic pleasure of hand made tiles and theirweathered appearance give peg tile roofs a specialpatina and character. Modern substitutes, whichlack these variations often result in a dull andmonotonously uniform roof.

Weight3.36 Clay tiles, depending on design, can varybetween 39 and 71 kg/m2.

26

supporting roof coveringsare given in the EuropeanStandard BS EN 508 Parts 1,2and 3, which are for steel,aluminium and stainless steelrespectively. BS EN 506applies to copper or zinc self-supporting roof coverings.Gutters for metal covered

roofs are often to be found formed integrally withthe roof covering. Movement joints will be neededin long gutters of all metals. Corrugated metalroofs have often replaced thatch and tile onoutbuildings for over 100 years. Painted eitheroxide red or black, they cover the roofs of manyhistoric buildings (often barns), having preservedthem against the weather when the original roofcovering had failed. Corrugated metal roofs lookquite different from modern metal sheeting. Theirpreservation, or replacement on a like for likebasis, is advocated.� Glass can often be used to great effect, and iflow-emissivity and solar-controlled coatings arespecified these can offer relatively highperformance.� Concrete tiles should conform to BS EN 490.Despite efforts to produce them with a variety ofprofiles and a dressed surface to emulate clay, theoriginal material should always be the first choicefor a building in the Chilterns. Dressed concretetiles do not weather as satisfactorily, and nevermatch the rich colour and texture of real clay tiles.

Material Choice andCombinationsChecklist� Do experiment with combinations of materials

on complex and hierarchical roofs� Do use slate quarried in the UK� Do use lead or clay detailing in association

with slate� Do specify long straw thatching except where

an existing roof is coated differently

� Don’t specify concrete tiles� Don’t spoil good tilework by combining it

with materials of poor quality

Material SelectionandSpecification

3.34 In all cases, ensure the finishing material isappropriate for the performance, life and aestheticrequired. Ask to see a current, independent testcertificate, including, but not limited to BritishBoard ofAgrément certification.Ask to see builtexamples of types similar to that being considered- ideally they should be at least 10 years old.

3.35 For the remainder of this section, it isassumed peg tiles have been selected. Peg tilesare one type of plain tile, the term used for allsmall-format tiles. The subtle variations and


Steel roofing simulatingprofiled tiled roof – notethe fixings! (HemelHempstead)

Machine-made tiles cannot match the subtle textures ofhand made ones (South Chilterns)

A traditional waney roof for contrast



27

Durability3.37 Tiles meeting the stringent requirements ofBS EN 1304 have demonstrated they have thenecessary durability for the UK environment. Claytiles are unique in that they weather favourablyand mellow with age. They can improve withexposure.

Thermal capacity3.38 The thermal insulation contribution of claytiles and batten cavity can be ignored. Insulationshould provide the necessary thermal performancefor the building.

Fire resistance3.39Clay tiles carried on timber rafters, with orwithout underfelt, sarking or boarding are listed ashaving notional AA designations in respect ofpenetration by fire and flame spread under TheBuilding Regulations 2000Approved Document B.Clay tiles are deemed to satisfy the UK BuildingRegulations with respect to external fireperformance. The European external fire test willnot apply to clay tiles because they areincombustible and have a reaction to fire ratingbetter than class A2.

Colour3.40 Awide range of clay roof tiles is stillavailable - variations are obtained by controllingthe kiln atmosphere to produce rich heather

shades. Colour can also be enhanced through thefiring process to create a brindle effect, whichvaries the colour between the outer edge and thecentre of the tile. Red/orange colours, whichmatch original clay tiles as closely as possible,look best and are those that the ConservationBoard recommends. Tiles should always be mixedfrom at least three pallets to ensure that anyvariations in shade and colour give anaesthetically pleasing effect.

Size3.41 The standard size for plain tiles is 265mm x165mm, although smaller sizes down to 255mm x160mm may also be encountered. Peg tiles arealmost invariably smaller than ‘plain’ tiles.

Shape3.42 Peg tiles present a wide variety of cambers,which is what makes them interesting. Singlecamber tiles curve from top to bottom whichreduces the capillary action between courses.


This roof demonstrates a failure to mix tile batches

Double or cross camber tiles are also curved fromleft to right and should be the preferred choicealthough single camber tiles may be moreappropriate to many Victorian/Edwardianproperties (and new houses in styles echoingthese periods) where a flatter profile is oftenencountered. Profiled tiles are in widespread use,but there is little tradition of these types in theChilterns and their use does little to enhance orrespect the distinct character of the region.

Fixings3.43 Peg tiles are not, of course, nailed. Moderntile pegs are generally aluminium alloy, the largerthe head the better. Very old tiles often have over-large peg holes and for these two pegs can beinserted in one hole. Galvanised iron pegs are stillavailable but will rust eventually; they are oftenalso too short. Tile clips are not traditionalfeatures of Chiltern peg-tile roofs. Fixings arecovered in BS 5534.

Specials3.44 Ornamental tiles can have curved edges suchas the club and bullnose or beavertail ornamentaltiles, a fishtail shape or a pointed end, commonlyknown as diamond or arrowhead ornamentals.Overuse of special tiles can result in a fussyappearance; and, as they are often placed invulnerable or exposed situations, maintenancerequirements and the future availability of



28

accurate replacements should also be borne inmind.

Workmanship3.45 The code of practice BS 5534 (covering bothslating and tiling) should be followed, althoughthis is currently being revised. BS EN 13748-2:2004covers tiles intended for roofing applications.Tiles should have a gap of up to 3mm between

them. The headlap specification in BS 5534 is 65mmminimum (75mm is recommended in exposedareas.) Batten gauges should fall between 88-100mm and staggering the battens will increasethe stability of the roof. The sidelap should be notless than one third of the width of the tile,typically 55 mm. These lap arrangements willprovide good protection against rain and snow.

3.46 Peg tiles are not nailed: rather they are oncepegged to allow them to be aligned in horizontalcoursing. The minimum fixing specification forplain clay tiles is to fix every fifth row (dependingon wind calculations) and at all ridges, eaves andverges. Every tile should be nailed twice onpitches of 60° or steeper.

3.47 For setting out purposes, the eaves tileshould overlap the gutter by 50mm. With pegtiling a tile cut in half is often encountered as theeaves course, bedded face down in mortar on asawn tilt fillet. The top tile is similar but beddedface up onto the last full course.

Tile Checklist�Do design new roofwork to a highspecification

�Domix tile batches to create a balancedvariation of colour (in the orange/red colourrange) on the roof

�Do ensure tiles with appropriate camber areselected

�Don’t overuse specials


Fig 2: Drawings of specials

Pointed(Arrowhead)

Club

Pointed andStep

Bullnose andFishtail

Pointed andBullnose

Club andFishtail

Bullnose(Beavertail or Spade)

Fishtail

Fig 3: Sketch showing typical tiled pitched roofwith terms used

Side lap

Tile battensBattens/tilegaugeTile headlap

Eaves course tiles

Roof battened out (Brook End Farm)

Step



29

Openings

4.1 Early buildings with low rooflines often hadupper storeys with dormer windows –sometimescreated as a result of the insertion of an upperfloor. In larger houses, servants were oftenaccommodated in roofspaces and were lucky ifthat space was lit by anything else than windowsin the gable ends.

Dormers4.2 Dormers can take many different shapes, butcertain types are more traditional in the Chilternsthan others - simple unadorned pitched andgabled dormers are frequently encountered. Indesign terms, it is vital to proportion and scale thedormers correctly in relation to the roof mass.Dormers may require special provisions forventilation. Flat roofs over dormers are oftenpoorly ventilated. Secret gutters can be formedround most dormers, without altering theappearance of a traditional dormer. Mansard roofs,either of slate or tile, from the 18thc. often had moreelaborate sash windows. These need carefuldetailing, particularly where the roof changesplane. It is often difficult to ventilate roofstructures over dormers and ‘warm’ roofconstruction may have to be used. However,Building Regulations governing ‘U’Values in

Chapter 4Detailing the Roof Traditional dormers - well proportioned

Dormers - poor proportions or detailing

Dormers - less common design but appropriate to the building

Chapter 4 : Detailing the Roof



30

Eaves, Verges andRidges

Eaves4.5 Overhanging eaves may be ‘closed’ or ‘open’,referring to whether the projecting ends of therafters are boxed in. In the Chilterns, ‘traditional’eaves are ‘open’, sometimes incorporating afascia.A300mm overhang is sometimesrecommended to protect the wall, but again,‘traditional’ eaves tend to be less pronounced.There is a presumed advantage if the overhangcan be provided with a drip e.g. a tile with a sharparris to the under-surface. This eaves course oftiles should be set at the same pitch as the generaltiling, achieved byfixing a timber fillet atthe base of therafters. Where afascia is used withopen eaves, it shouldbe kept proportionateto the depth of therafters. Upvc shouldbe avoided. The topof the fascia boardshould be set at thecorrect level so thateaves courses of tilesare at the same pitchas the tiling ingeneral.

relation to dormers maybe relaxed in theAONB,allowing simple,traditional designs to bemaintained.

Rooflights4.3 Rooflights are not‘traditional’ features of

Chiltern buildings and should always be usedsparingly and discreetly. However, in buildingsundergoing conversion where light has to beadmitted into a roofspace where previously therewas none, rooflights will tend to be the preferredoption over dormers because visually theypreserve the existing roofline (and usually do notrequire planning permission). A further distinctionneeds to be drawn between rooflights (a simpletop-hung device, often with a single glazing bar)and a roof window (with centre pivot). Simplerdesigns (e.g. ‘The Conservation Rooflight’)should be the preferred option. Rooflights that sit‘in’ the roof with secret gutters are more discreetthan those which sit ‘on’ the roof with flashedabutments. There is no British standard for rooflights. The rules governing their selection and useare complex. Roof lights may be designed andinserted as a means of escape and therequirements for size, opening method and heightabove floor level should be addressed. Analternative to providing daylight and ventilation is

to consider the useof sun pipes whichmay be appropriateon less prominentroofs, though eachscheme will need tobe considered on itsown merits.

Lanterns, Cupolasand Bellcotes4.4Grander buildingssometimesincorporatedbellcotes, lanterns orcupolas (the latterbeing domed), usually constructed of timber, leadand glass, to light stairwells etc. Some cast ironvariations were introduced in the 19thc. Lanterns,often in Upvc nearly always look clumsy andoverfussy on more modest buildings.

OpeningsChecklist� Do use openings in roofscapes sparingly� Do use timber for windows, lanterns etc.

� Don’t oversize openings� Don’t specify a dormer if a rooflight will

perform the same function

Rooflight in roof ofmachine-made tiles(Berkhamsted)

Bell turret (Berkhamsted)

Open eaves (Berkhamsted)




31

4.6 Some Classical designs may incorporate deep‘closed’ eaves fashioned with modillioned cor-nices. In general, however, the boxing in of eaveswith soffits should be avoided, they interrupt anotherwise simple transition between wall and roof,and tend to be peppered with vents to compen-sate for sealing up the roofspace. (Over-fasciaventilation avoids the need for soffit ventilation).Angled transitions in theeaves, e.g. where a gable isintroduced, can look particu-larly clumsy. Where soffitshave to be used, boards shouldbe nogged, otherwise saggingmay occur. Soffits of plastic orfibre cement board are notrecommended.

4.7 With some kinds of roofstructure over thick externalwalls and roof pitches steeperthan 45o, there may be difficulty

in obtaining a good overhang at the eaves and, atthe same time, give adequate clearance for windowheads. This may have been the reason for the useof sprockets to give a suitable overhang withflatter pitch. Nailing or bolting sprockets to thesides of rafters, where the fixings operate in shear,is probably better than nailing them to the top ofthe rafter.

4.8 Where the eaves are kept open, a timber filletshould be fixed to set the eaves courses of tiles atthe same pitch as the general tiling. Screens toprevent ingress of birds can be used, oralternatively a proprietary rafter spacer tray withintegral screen can be used.

4.9 Where over-fascia ventilation is beingprovided, a timber batten shouldbe fixed to the outer edge of themasonry to provide a fixing forthe ventilator.

4.10 Although there is littlesurviving evidence that peg-tiles were ‘torched’, mortar isused in a number of details.Tiles to be bedded on mortarshould be docked (wetted)beforehand. Caution needs tobe exercised as rainwater run-offfrom fresh mortar may stain tiles.

Boxed eaves (Potten End)

Deep projecting 18thc. eaves with modillioncornice (Hemel Hempstead)

Fig 4: Eaves with over-fascia ventilation

Fig 5: Eaves with soffit ventilation


Spacer tray

Over fasciaventilator

Underlaysupport Air path

75mm

Spacer tray

75mm

Air path

Soffitventilator

Underlaysupport



32

Verges4.11Although there is a requirement in BS 5534for all edge tiles (and slates) to be mechanicallyfixed, in practice this is more or less impossible toachieve. Instead the half tile is usually bedded inmortar. In plain tile and slate, verges can becanted upwards to assist in diverting water awayfrom the verge (which also has the added effect ofcountering a potential optical illusion of saggingwhere the roof surface runs through without suchcanting).

Bedded Verges4.12 The underlay should lap onto the outer skinof brickwork by 50mm or in the case of anoverhanging verge, onto a flying rafter (see BS800: part 6: 1990 sections 3 and 4). In many casesthere is no undercloak and the mortar is struck

flush with the wall orbarge rafter. Wherean undercloak courseis used, the tiles,placed face sidedownwards, shouldproject from the wall(or bargeboard) by atleast 1˚” (35mm),preferably 2" (50mm).The top of each tileshould rest about5mm above theundercloak tile. Thebottom will touch thetile below it, and thespace between is pointed up with mortar (seeFigure 8). Theuse of tile insertsas a form ofdecorationbetween the tilesurface and theundercloaking,similar to thedentil slips usedon ridge tiles, canhelp tominimizethe appearanceproblems causedby cracking.A Bedded verge with overuse of

mortar (Hemel Hempstead)Plain bedded verge (Medmenham)

Contrasting verges – half-tileslips to left, tile-and-a-half toright. Note also the valley tiles(Tring)


Fig 6: Open eaves with breathable underlayand counterbattens

Fig 7: Cottage eaves with breathable underlayand counterbattens

75mm

Timber tilt fillet

Breathableunderlay

Eaves tray

Underlaysupport

Breathableunderlay



33

variation of this detail is to use a doubleundercloak. Plain tiles should not be used forundercloaks on roof slopes of below 30° pitch.Tiling battens should be carried over theundercloak and finish 100mm from the verge edge.Half slip tiles are preferable to tile-and-a-half tilesin the case of peg tiling. Always avoid the use oftile-and-a-half tiles of different manufacture, e.g.pink concrete, or Staffordshire, where a piano-keyboard effect results. The bedding, using a limebased mortar, between the top verge course andthe undercloak course should be c. 75mm wideand finished flush, leaving the edges clean.

Substitutes such ascement fibre boardor similar are notacceptable. Crow-stepped gables andcoped gables areonly occasionallyencountered in theChilterns –principally onestate buildings.

Cloaked4.13 Cloaked verges (using special handed tiles),dry-laid to form a downstand, are not common inthe Chilterns.

Bargeboards4.14 Bargeboards may contribute to the characterof certain buildings, and might tend to give moreprotection to the wall. However, if built of timberthey will be subject to wet rot. Plastics are nottraditional. The inboard edge of the gable shouldbe securely fixed to the rest of the roof, and careshould be taken to ensure that the cantilevereffect of the tiles does not impose too great a loadon the bargeboard. The underlay should lap ontothe flying rafter, and carried over to meet with theundercloak. (see BS 800: part 6: 1990 sections 3and 4). Again, the tile undercloak course shouldproject from the bargeboard by at least 1˚”(35mm), preferably 2" (50mm).

Fig 8: Bedded verge

Verge with cogged brickwork(Marlow)

Cloaked verge (Berkhamsted)

Plain timber bargeboards, echoed on the formerporch (Monks Risborough)


Undercloaktile

Rafter againstinside wall

Tilesembeddedin mortar



34

Ridges4.15A great variety of shapes of ridgetile is available. Most roofs in theChilterns have a shallow, roundedprofile (third-round rather than half-round) and often with a slightsaddleback effect. Ridges are oftenhand made in similar colours andtextures to peg tiles and are often ratherirregular in line due to slight variationsin size and shape. This irregularity,within limits, can add considerableinterest to an old roof. Some Victorianand Edwardian buildings will sport moreelaborate crested ridge tiles. Traditionalpractice is to bed them solidly onmortar.A1:3 mortar mix can be used forbedding, preferably air entrained, butthis is a comparatively strong mix andcould lead to cracking. A high durability

mortar is nevertheless required, and an airentrained 1:0.5:4.5 cement:lime:sand is analternative. Underlay from one side of the roofridge should overlap the underlay on the otherside by not less than 150mm. (For mono pitchedroofs, underlay should extend over the mono ridgeand top fascia board by not less than 100mm).Finishing courses should be secured over the toptiles. Ridge tiles should be laid by continuouslybedding their edges and solidly bedding with tileslips inserted into the mortar at ridge joints.

Where masonry walls support or abut a ridge, allridge tiles within 900mm of such walls must bemechanically secured by fixing (with nails, clips orwire etc) into the supplementary ridge tile fixingbattens as recommended by the manufacturer. Theends of ridges at gables should be filled withmortar and slips of tiles finished flush.

4.16 Dry fixed ridge systems exist but are notillustrated here as they are not traditional to theChilterns. Modern ridge ventilation systems arealso not traditional and can be unsightlyinterrupting the ridge line. It may be possible tocut back roofing felt each side of the ridge apex by300mm to allow roof void ventilation together witheaves ventilation.

Finials4.17 Purpose made finials on earlier roofs do notseem to suffer much from storm damage. Somedecorative finials, usually of terracotta, are stillavailable and can enhance the finishedappearance when used sparingly and on roofs ofsuitable stature.

Valleys4.18Valleys are created using either a metal liningor purpose made valley tiles, which becamecommon in the latter half of the 19thc. Valley tilescan be supported on two raking battens, one toeach slope; these help to protect the felt fromprojecting batten ends. Valley tiles can rarely beused across roof slopes of different angles. Onmajor buildings, valleys may be swept or laced,

Ridge with crested ridge tiles and finial


Valleys, HipsandAbutments

Fig 9: Bedded ridge

Third-round ridge(Hemel Hempstead)

Tile slip in solidbedding at butt jointContinuous

edge bedding



35

either to a radius oran acute angle. Adouble thickness ofsarking felt isrequired and theunderlay should belaid from side toside and eachcourse should lappast the centre-lineof the valley by notless than 300mm.Where acontinuous lengthof underlay is laidin the valley, each course of felt from either sideshould be cut to mitre at the centre-line of thevalley and lap onto the continuous length by not

less than 300mm. Metaland plastic valleymaterials and unitsshould not be laiddirectly onto feltunderlays because of therisk of adhesion, whichcan inhibit the freedrainage of any moistureor cause the prematurefailure of the valleymaterial. Lead, if used,should never be laid

Valley being formed for valleytiles (Hemel Hempstead)

Fig 10: Valley – Tiled

Valley formed withvalley tiles (Tring)

Valley formed in slateroof with metal liner(Berkhamsted)

directly on an unsupported membrane. It shouldalways be supported on lay boards, which needsto be nogged between, or cut into, the rafters.Tiling battens may require additional supportwhere they abut the valleys. Valley gutters slopemuch more shallowly than the pitch of the roofsthey join, and on pitches of less than 20° areparticularly prone to leaking. Gutters may berequired on porches and bay windows. Openvalleys formed with metal lining or pre-formed GRPare not recommended.

Hips4.19 Hips in plain tiled roofs are usually formedwith ridges bedded in mortar and held at the footon hot dip galvanised hip irons or hooks. For roofpitches under 35° they can be 4mm thick; but over35° they should be a minimum of 6mm thick. Sincethe 1970s it has become more common to clip eachridge tile to the hip rafter. Alternative methods offorming hips, possibly giving a neater appearance

Hip prior to being covered with hip ridges. Thisillustrates poor practice. One facet should have beencompleted, the hip ridges being put on as the other facetwas going up. (Hemel Hempstead)


Valley tileExtra width of underlayto valley

Layboard

Fig 11: Valley – LeadLongitudinalbatten

Tile batten



36

flashing then laps the soakers by 50mm – more if itcan be arranged. Underlay should be turned upthe abutment by not less than 50mm under theflashings.Alternatively, soakers with 50mm maybe suitable, using 240mm lead, allowing 100mm offlashing to extend over the tiles as well. Theupstand would have 50mm to the ‘water line’before the innermost point of the cut for eachstep, and 25mm turned into each joint.For a brick

Hip with half-roundbonnet tile. Note thebonnets are poorlyaligned with the tilecourses. (Berkhamsted)

and possibly improved performance, includepurpose made hip tiles. Bonnet hips were a featureof Sussex and Kent, and only appeared in theChilterns in the mid 1930s. Mitred hips in plaintiles should be laid over soakers lapping at least

Fig 12: Hips with hip ridge tiles

Hip using half-round tiles (Berkhamsted). Note also theintrusive satellite dish and aerial

Hip with lead roll (173 High St., Berkhamsted)

Hip iron (HemelHempstead)


Third round hipridge tiles

Fig 13:Top edge and side abutments with metal soakers

Front apronflashing

Stepped flashing

Metalsoakers

Front apronflashing

100mm to each side of the hip. On hips, underlaycourses should overlap at the hip line by not lessthan 150mm.

Junctions4.20 The underlay should overlay the roofjunction by a minimum of 150mm in each detail.

Abutments4.21 Late Victorian terraced housing in particularmight include separating walls projecting throughthe roof. Cement flaunching is often used, butmetal flashings over a secret gutter or soakers arebest. Copings usually require kneelers to preventthem slipping. Where a pitched roof abuts aseparating wall in a stepped-and-staggeredsituation, part of the roof becomes anexternal gable, and the outer leaf of themasonry becomes an inner leaf belowroof level. Particular care is neededto ensure that rainwater isprevented from reaching theinterior. Soakers for plain tilesshould be a minimum width of175mm to give an upstand of75mm against the wall, and a lapof 100mm under the tiles.AcoverHip iron



37

abutment, the underlay should be detailed to lapover the material forming the back gutter by100mm to 150mm, depending on the pitch of theroof. Ponding or water traps behind the tilting filletshould be prevented by design. In lieu of leadflashing sometimes cut tiles, set an angle andbedded in lime mortar at junctions to provideweather protection, can be an alternative detailand are probably the only way to flash a roof to anexisting flint wall.

Details Checklist� Do ensure consistent use of appropriate limemortars

� Do ensure dressings are correctly detailed� Do use appropriate lime mortars� Do use half-slip tiles at verges rather than tile-

and-a-half tiles� Do proportion the eaves overhang� Do ensure valley tiles or hip bonnets are

appropriate to the building or local area

� Don’t specify half-round ridges unless the roofis steeply pitched

� Don’t specify cloaked verges� Don’t specify plastic bargeboards, fascias etc.� Don’t over-embellish roofs with unnecessary

details� Don’t spoil good tilework with ‘sloppy’ or

‘smeary’ mortars

Elegant wrought irongutter brackets(Ewelme)

RainwaterGoods

4.22 Cast iron or aluminium, or in some cases,lead, will be more appropriate to use rather thanplastic. BS 6367 covers rainfall rates to beprovided for and therefore the size of gutteringrequired. If gutters are undersized, water spillagecan saturate walls and lead to dampnessinternally. Positioning down pipes in the centre ofruns of guttering rather than at ends will reducethe maximum water load on gutters and help toprevent surcharging and overflow. Gutters shouldbe fixed with a slight fall to allow for some verticalmovement.Afall of about 1 in 350 (10mm per 3mrun) is recommended. Roofs of a more complexdesign will need special calculations to therequirements of BS 6367. The provision ofgratings over rainwater pipes and outlets ingutters is a matter for judgement. BS 6367recommends they are not provided in outletssmaller than 150mm; wire or plastic balloons maybe a better alternative. Where downpipesdischarge onto a lower roof, if it is of tile (or slate)the discharge will fan out before reaching thelower gutter – not the case with heavily profiledtiles. Weirs or overflows should be incorporatedin the design to prevent spillage of water over thesides of the gutters. It is wise to design to ahigher code than set out in the standard. Siphonicdrainage systems can remove large quantities ofwater from a roof quickly, although maintenancerequirements are even more severe.

4.23 If gutters are undersized, waterspillage can saturate walls and lead todampness internally. Careful detailing isrequired where underlays extend into thegutter. Underlays of BS 747 class 1F donot perform sufficiently when exposedand should be reinforced with a moredurable felt, e.g. type 5U as specified inBS 747, or a proprietary eaves device.

4.24 One common occurrence is that ofinadequate support for wide valleygutters in pitched roofs, with theconsequent risk of fracturing or puncturing thesurface of the gutter. If lead is used, it should bein accordance with the relevant technicalguidance.

4.25 Box gutters can easily become blocked withdebris, and because they are hidden, tend tosuffer from lack of routine maintenance. Designand implementation should be in accordancewith the relevant technical guidance.

Fig 14: Box gutter eaves


Lead

Timber



38

Chimneys, Flues andVentPipes

4.26 Stacks are increasingly being omitted fromnew buildings where heating systems no longermake them a necessity. Maintenance problems aretherefore reduced - chimneystacks are inevitablyexposed to the ‘elements’ and to reactionsbetween vastly different internal and externalenvironmental conditions. Mortar flaunching usedas flashing may for example crack and eventuallyfall out allowing moisture to penetrate the roof,leading to timber decay and dampness. However,roofs can look particularly stark withoutconventional stacks, and to omit them is to denythe possibility of heating rooms using an openfire. With pressure mounting to consumesustainable, renewable resources, the possibilityof a reliance on wood as fuel – particularly in the

Chilterns - should beaccommodated at thedesign stage. Pointingand flashings need tobe particularly robust.Tile fillets aroundchimneys almostinevitably shrink fromthe brick as the roofmoves, and let inwater. Stepped leadflashings are almostinvariably preferable.Flashings often haveinsufficient upstands (sometimes as little as 50mm)- even 150 mm deep flashings may be defeated bystrong winds, rain water systems backing up ordrifting snow. Flues should avoid piercing the roofin visually sensitive areas; lead (or other shapedmaterial) round SVPs is often not large enough to

Chimneyless roof (Kingshill)

Brick chimney withtraditional detailing(Chiltern Open AirMuseum)

lap adequately with the adjacent tiles. Airadmittance valves can often be used to obviatethe need for a soil stack to penetrate the roofcovering.

Fig 15: Pipe flashing

Leadwork to flashingsand valley(Beaconsfield)

Lead flashings (HemelHempstead)

Mortar flashing(Berkhamsted)

Tall brick chimney,recently repointed (LittleMissenden)

Pipe flashing (Hemel Hempstead)


Welt

100mm

150mm



39

Chapter 5Sourcing andSelection

Chapter 5 : Sourcing and Selection

Selecting aContractor

5.1 Ensure the contractor will keep to thespecification. The roofing sector is competitiveand contractors might promise cheaper or bettermaterials – these offers should nearly always betreated with suspicion. Check contractors byvisiting other sites they have worked on andconfirm they observe all Health and Safetyrequirements (particularly the Working at HeightRegulations). Undertake a full risk analysis andeliminate any obvious risks. Ensure no complexprocedures take place at height – especially inconfined areas. Ensure that adequate guarding

Roofing work requires rigorous health and safetymeasures to be in place

and protection are written into the documentation.Wherever possible, avoid or prohibit the use ofconstruction processes that have a fire risk.

ObtainingRoofingMaterials

5.2 Recent evidence of the increase in the use ofclay tiles is demonstrated by the 50% increase inthe volume of clay tiles produced and sold eachyear since 1995. The number of suppliers isgrowing to meet this demand – contact theChilterns Conservation Board for details.

5.3 If salvaged tiles are being used, nails or pegsshould be removed carefully, before stacking, toavoid damaging the holes. Broken, cracked orcrumbling tiles should be discarded and further

recycled unless they can becut for eaves, verges or tops.Tiles should be stacked onlevel ground on boards raisedup on blocks. They should becovered with waterproofsheeting during storage.Stacks should not exceed 3layers to avoid the bottomlayers being damaged by theweight of those above. Tilesshould be stacked verticallyon their long edges. When so

stacked on a scaffold they drain quickly when itrains. If stacked on their faces they retain thewater and are also more likely to crack.

5.4Roofing merchants are often extremely knowl-edgeable and may keep or know of sources ofsecond-hand materials. However, they must betechnically appropriate for new work and shouldalways be carefully sourced.

Prototype Chilterns tiles, 2007 (H. G. Matthews)



Repairs andMaintenance

6.1 Gutters and rainwater hoppers should becleared out annually (BS 6367); more frequently iftrees are in the vicinity. The condition of guttersupports should also be checked. Plant growthwill often affect gutters and ivy can penetrate thejoints between slates and tiles. Careful removal isrequired so as not to further damage the roofcovering. Green algal growth, lichens and mosscan occur on many roofs. These natural growths,if not excessive, can add still further textural andcolour interest, although they can increase the riskof frost damage to porous tiles and may interferewith drainage occasionally. Careful brushing off,rather than use of power jets or proprietarysolutions (bothof which cancause terribledamage)willthen benecessary. Leadcan be treatedwith a patinationoil to preventstaining where it

lies above susceptible tiles, slates or glass.Chimneys should be regularly inspected toensure: they are exactly vertical; that the pointingis sound; that flashings are not lifting and areproperly wedged into mortar; that any pots are notcracked or damaged, and that the pot mortar is notcracked or lifting.

6.2All old clay tileroofs will haveweathered, often to afar darker red-browncolour than theoriginal distinctly red/orange or paler red/brown colours.

Provided they have been properly fired and fixed,the tiles should last 100 years and more, thoughmanufacturers’ guarantees tend to be for much lessthan this. All types of tiles can suffer nailcorrosion. Older tiles with nibs, especially theEtruria marl types, are the ones most likely todelaminate. Some older tiles may be found to beunderburnt, giving rise to delamination anddeterioration. They do not ring true when tapped,and some can be snapped by light hand pressure.The odd tile may therefore need replacing fromtime to time, most probably after strong winds. It isoften difficult to achieve a very close match – greatcare is needed in selection. The mixing of modernsmooth machine made clay plain tiles or concretetiles in with an old tile roof is not acceptable. Apartfrom spoiling the aesthetic purity of an old roof by‘spots’ of alien materials, they can look very oddwith ‘lanes’ or courses of jarring tiles, where

Poorlymaintained gutter(Lewknor)

Lichen growth (Bledlow)

Debris in outlet(Tring) Patched repairs (Berkhamsted)

40 Chapter 6 : Repairs, Alterations andExtensions

Chapter 6 Repairs, Alterations and Extensions



41Chapter 6 : Repairs, Alterations andExtensions

thoughtless repair has been undertaken. Equally,because peg tiles tend to be smaller than otherplain tiles; the latter should not be used forrepairing peg-tile roofs as forcing in an oversizedtile will cause the others to ruck up or break. Tilesfrom the Loughborough area are usually 11" x 7"and are also not compatible with peg tiles.

6.3 Sprayed treatment of undersides of roofs isnot recommended; completely ‘wet poulticing’ thebattens may possibly lead to rot. It will alsoprevent traditional roofing materials beingsalvaged for reuse and make further traditionalrepair difficult if not impossible. Such treatmentmay also result in restricted roof space ventilationwith the consequent risk of fungal and insectattack to roof timbers.

6.4 Where the tiles havecome to the end of theiruseful life, it will benecessary to strip offthe existing roofcovering. Matching like-for-like traditional repairwill not require listedbuilding consent, but itis advisable to agree

Verge poorly repairedwith tile-and-a-halfreplacements(Berkhamsted)

Tiled roof in poor repair(Hemel Hempstead)

this work in advancewith the ConservationOfficer. Considerchanging fromconcrete tiles or othermaterials to a clay tileroof. It is oftenpossible to convert aflat roof to a pitchedroof, allowing tiles tobe used. The use ofunsuitable modernproducts can damage

a building’s resale value, and its structure. Whenre-roofing with tiles, it is often possible to salvage75% of the original roofing. Great care will need tobe taken in removing and stacking. Tiles shouldbe inspected as they may help to document thehistory of the building. Nails and pegs should beremoved before stacking. In cases where roof

pitches are concealed from public view, thesalvaged tiles from the original roof should beused on the prominent slopes.

6.5Apart from replacing tiles that are cracked ordelaminated, repairing a roof will offer anopportunity to strengthen a weak roof structure –however excessive ‘straightening up’ should beavoided. Therefore only those timbers affected byrot etc. should be repaired; sagging or twistedpurlins, spreading rafters, and rotating wall-platesshould be reinforced or replaced only if theycompromise the performance of the roof. Theopportunity to replace old sarking and improveflashings round chimneys should always be taken.Any project involving the replacement or re-roofing of a roof involving more than 25% of itsarea requires the insulation within the building tobe upgraded to comply with Part ‘L’BuildingRegulations.

Flat to pitched roof conversion (Christmas Common) (Highly Commended in 2005 Design Awards photos byA. Ingram and C. White)



Roof timbers under repair (above) and roof beingstripped (below) both at 173 High St., Berkhamsted

Roof tile inscribed‘John Babb 1745’(Chiltern Open AirMuseum)

Pigeon-proofing(Hemel Hempstead)

42

6.6 Care is needed to detail gables, verges, ridges,hips, abutments, parapets, eaves and valleyscorrectly. In most situations, cut slip tiles shouldbe used at gable verges, not modern tile-and-a-half purpose made tiles. Ornamental tiles shouldbe preserved as they can add to the character of abuilding. Where tiles are banded, the coursingshould be accurately recorded and recreated whenthe new roof is laid. Existing profiles andmouldings of bargeboards and fascias should bematched. Original rainwater goods should bemaintained and retained. Oak pegs and riven oaklaths should be reinstated or replaced like-for-like– especially where the underside of the roof isvisible – as in barns or outbuildings. Originaltorching, where the tiles are in good condition,should be repaired with lime-hair mortar.

6.7 Bats are particularly attracted to old roofs andit is a criminal offence under the Wildlife andCountrysideAct 1981 to intentionally injure ordisturb a bat, damage a bat roost or obstruct theentrance to a bat roost. Swift nests should not bedisturbed. Infestation of roofs by edible dormice(Glis glis) is a problem in parts of the Chilterns.Their removal requires a licence issued under the1981Act. Grey squirrels can be a problem not leastto electric wiring insulation. They, and largervarieties of insects, can be excluded by aprovision of a 3-4mm mesh over ventilation slots.Pigeon-proofing measures can help prevent roofcoverings being fouled by droppings, but thesolution of using wires and pins can itself beunsightly and may damage historic fabric.

6.8 Traditional roofing materials in the Chilternsshould not be replaced withalternatives and consent will certainlybe required if on listed buildings.Consent is also required if a proposed‘repair’ is not a like-for-like repair.Legislation relating to roofs coveredwith asbestos tiles or sheeting shouldbe strictly observed. If the roofcovering is being changed, it is alsoadvisable to discuss the work withofficers to determine whether a formalbuilding regulations applications isrequired. For example, the increase in

dead load when Welsh bestsare replaced with concretetiles can be as much as100%. The BuildingRegulations 1991ApprovedDocumentA provides forsuitable calculations to bemade for such replacementcoverings. Where a roof isbeing re-covered adjacent toa roof which is remaining,attention must be paid toachieving weathertightness of the joint betweennew and old.

6.9 Where slate roofs are encountered,replacement of the occasional slate due forexample to ‘nail sickness’ (corrosion of nails) is

possible by using a tingle insertedunder the slate above, and turning upits tail to retain the inserted slate. Thetop of the inserted slate must be madeto rest on the lip of the batten.Proprietary clips which can be nailedin the gap between the upper slatesare also available. When re-roofing isrequired, existing slates should be re-used whenever possible. New slatesare expensive and good qualitysalvaged slate is likely to last longerthan artificial imitations.

Chapter 6 : Repairs, Alterations andExtensions



43

6.10 Always seek appropriate expert advice whenmaintaining thatch. Trees should not be allowedclose to, and clematis and trailing plants should beremoved from, thatch. Chimneys should be kept ingood condition and the roofspace clear of dangerssuch as exposed electrical wiring. Materials maybe slipping or the surface coat may look messy,but cosmetic repairs may address these problemsrather than a complete rethatching. Restoration ofthatched properties sometimes leads tounnecessary, undesirable and damaging changes

to the roof’s appearance. Repair should be on alike-for-like basis. Recoating may add weight tothe present thatch – the underlying roof structureshould therefore be carefully checked, and thebase coat should be restored to a sound and levelsurface. Gables and eaves may need to be strippedout, and remedial works may be required to eaves,verges (including bargeboards) and chimneys.Ridges will require attention more frequently thanthe main roof covering.

6.11 Where repairs are required to lead andcopper, felt and bitumen is not an acceptablesubstitute. Lead cast in the traditional way ispreferred over milled lead; more recently,industrially produced cast lead sheet has becomeavailable.

Conversions

6.12 A consequence of flatter roof designs islower lofts and less roof space, reduced further bybeing used for water tanks, pipes, aerials etc. If theroof is of trussed rafter construction (mainly post1965) the roof will need to be rebuilt using steel tofree up the loft space occupied by the closelyspaced W trusses; the loft floor may also requirestrengthening. Detached houses built in the 1970sand 1980s may well require elevation of theroofline to achieve the required ceiling height.Building regulations will apply particularly tostructural considerations and fire planning.Internally, traditionalstairs will give safe andeasy access; other typeswill gain approval onlywhere space is restricted.For two storeys, theroute must discharge to adoor leading to anexternal safe place andnot in a room. Escape

Changing roofing materials may impose additionalloads on the roof structure and may detrimentally affectthe character of the building (Hemel Hempstead)

Chapter 6 : Repairs, Alterations andExtensions

Tingles (Berkhamsted)

Loft conversionsshould have aminimal impact on theexisting roof. Notealso the use ofdiamond patterns inthe tiles (Flaunden)

Alterations to this former tile and thatch roof haveradically changed the building’s appearance (Aldbury)



Conversions of buildingsshould seek to minimizethe impact on theroofscape. Even here, TVaerials, vents androoflights break up theformerly unobstructedroof covering.(Leverstock Green)

windows need to be largeenough and positioned foreasy rescue by ladder. Dormersshould be built with a warmdeck roof, and cupboardsshould be within the insulatedenvelope to ensure continuityof the lining. The rafters of attictrusses normally allowadequate depth for ventilation

over insulation.

6.13 Conversions of existing buildings from oneuse to another will impose design and possiblystructural alterations on an existing roof.Requirements for skylights or dormer windows willbreak up the roofscape and require carefulconsideration so they do not affect the overallstability of the roof. The requisite permissionsshould be sought at an early stage – planningpermission for change of use and listed building

or conservation area consent ifthe building is so protected.

Extensions andAlterations

6.14 Any extension should becarefully designed withparticular care being takenover roofslope and materials.

Extensions tend to be ‘roofing intensive’ and caneasily overwhelm an otherwise balanced exterior.Because of the inherent difficulties of extendingroofs on the same roofline and plane – whichoften results in an ugly and jarring transition ofnew and old tiles or slate – it is generally desirableto establish a break between the old and the new.Indeed extensions should usually be clearlysubordinate in bulk and form, and a physicaldistinction is likely to be desirable. Do nottherefore immediately assume that the roofingmaterial for the extension should match exactly theoriginal covering. Reclaimed tiles tend to ‘robPeter to pay Paul’ and it would be preferable toensure that any reclaimed tiles are used to repairexisting tiled roofs rather than used to create newones. Also it is clear that in the past alternativereadily available materials that came to hand wereoften employed to good effect. Main roofs of claypeg-tiles may have extensions of slate, or

sometimes pantiles, thatch or corrugated iron.Careful variation of materials on secondary roofscan thus considerably enrich a design.

6.15 Where extensions are being added to existingdwellings, the main roof may be found not to haveany sarking felt. Where this occurs at a valley, theold roof needs to be stripped back a shortdistance, and a batten laid along the length of thevalley over which the new sarking can be lapped.

� Do seek specialist advice for repairingtraditional roofs

� Do identify the causes of any roofing faultsbefore specifying solutions

� Do restrict repairs to the minimum necessary� Domatch replacement tiles with the existing

roof� Do ensure roofs of extensions blend in with or

complement existing roofs

� Don’t spoil roofs by introducing alien materials� Don’t use harmful cement based mortars for

repairwork� Don’t use spray treatments on the undersides

of roofs

44 Chapter 6 : Repairs, Alterations andExtensions

Well-designed extension –note the saddle ridge andslight change of pitch(Kensworth Church)

Well executed extension (Turville)

New slate roof to right poorly tied in to existing roof(Jockey End)

Repairs Checklist



45

Chapter 7Designing for Sustainability

Chapter 7 : Designing for Sustainability

7.1 Sustainability statements are becomingstandard requirements in planning applications.The role of the roof should not be ignored as itsdesign can improve the performance of the wholebuilding envelope. If carefully planned,sustainable features such as photovoltaic cells,solar thermal installations and sun pipes need notdetract from the overall appearance of the roof orbuilding. They can often be successfullyincorporated in ‘traditional’ designs, but they mayalso be particularly appropriate where a bold newdesign is being considered. Listed buildingconsent will be required for such additions to theroof slopes, and in some cases planningpermission will also be required. On some historicroofs such installations would always bedetrimental but panel arrays can be mounted onthe ground in locations where they would also beless intrusive in an historic building’s context. Abalance needs to be struck between the objectivesof conserving and enhancing the special characterof the AONB and the drive for renewable energy.

Photovoltaic (PV) Cells and Solar ThermalTechnology7.2 Solar power is an infinite source of energy,providing pollution and noise-free electricitywithout using extra space. The systems which

harness it are becoming increasingly economicallyviable and require little maintenance. The sun’senergy can be converted directly into electricityusing photovoltaic cells. Alternatively, solarradiation can be converted into heat by solarwater-heating panels. PV can also be incorporatedas canopies and skylights, and also in buildingfacades.

7.3 Grid-connect PV systems are connected to thelocal electricity network, which acts as an energystorage system, which means the PV system doesnot need to include battery storage. PVtechnology is ideally suited to use on slopingrooftops, where modules can simply be mountedusing frames. PV roof tiles are also now availablewhich can be fitted as would standard large formattiles.APV system might consist of a number of PVmodules connected together to give the requiredpower – typical modules have a rated poweroutput of around 75-120 Watts peak (Wp) each. Atypical domestic system of 1.5-2 kWp maytherefore comprise some 12-24 modules coveringan area of between 12-40m2.An inverter covertsthe low voltage DC to a higher voltageAC. Ameter, cables and switches to isolate the PVgenerator from the building and mains completethe system. A 2 kWp system for a house mightcost between £12,000 - £14,000 (tile type systems

tend to be more expensive). Grants may beavailable.

7.4 Domestic water heating systems consist ofsolar collectors mounted on the roof which heat awater tank via a circulating fluid. The overall areaof the panels is typically 3-4 square metres. Acontrol unit, connecting pipes, normal hot watertank, and back up heat source such as gas orelectric immersion heater complete the system.Aplane inclined about 30 degrees, facing the southwould be expected to yield around 1,250 kWh/m2in the Chilterns . The optimum angle for a southfacing collector is 0.9 multiplied by the latitude +29°. This maximises winter collection and reducesover-production in the summer. The optimum

Solar panels (Photo by C. White)



angle of tilt for the spring and autumnis the latitude minus 2.5°. The optimumangle for summer is 52.5° less than thewinter angle.

7.5 Design considerations includeoptimising the placing of the collectorstaking into account orientation (duesouth is the best possible), shade andavailable area, the choice of systemand whether planning permission isrequired. Seewww.greenenergy.co.uk

Rainwater Harvesting7.6 Rainwater harvesting is the collection andstorage of rain from roofs for future productiveuse. Water is a precious resource and yet much ofit is flushed down the drain. A simplerainharvesting system, with filtered water gatheredfrom the roof into an underground tank, canprovide water for toilets, washing machines andgardens, saving up to 50% of mains water used.The payback period for a domestic system iscurrently 10-15 years, and could be considerablyless for a larger scale commercial system.Asrainwater harvested from roofs can containpollutants, it cannot be used for drinking waterwithout suitable treatment. However, in a chalkyregion like the Chilterns, the use of soft rainwaterin washing machines etc. will avoid the build up of

limescale. Rainwater Harvesting forms onecomponent of an integrated approach toSustainable Drainage Systems (SUDS) Seewww.ukrha.org

Green roofs7.7 The environmental benefits of turf and greenroofs are widely recognised, in creatingbiodiversity, the opportunity to create outdoorroof gardens, savings on energy consumption byenhancing insulation, and providing a constanttemperature throughout the year. A ‘green’ roof isclearly more of an abrupt departure fromtraditional forms of roofing. However, they cansoften harsh edges of buildings in sensitiveenvironments, making them blend in with thesurrounding area. It is also perfectly possible toincorporate ‘living’’ roofs on discrete rearextensions. The two principal designconsiderations are that the structure is capable ofsupporting the weight of the material when fullysaturated and that the construction is watertight.A green roof will therefore usually consist of awaterproofing layer, which must be root-resistantor include a root barrier, a drainage layer, a filterlayer and the growing medium. However, methodsof construction differ between pitched and flatgreen roofs. Flat green roofs can either beextensive (ie have a thin layer of growing materialsuch as sedum matting) or intensive (ie greatersoil depth with shrubs and even trees). The

weight requirements for intensive green roofs aresuch that they are normally installed over concreteroof decks. Only contractors trained in green roofinstallation should be used. The system should besupported by manufacturers’ and contractors’warranties.For more information visitwww.livingroofs.org

Sustainability Checklist� Do use hand-made clay peg-tiles manufactured

in the region� Do design for re-usability� Domaximize the building’s performance by

careful roof detailing� Do design roofs to harness energy-saving

natural resources

Rainwater harvestingsystem, used for wateringthe greens (Little HayGolf Complex, Boxmoor)

Green roof (Berkhamsted)

46 Chapter 7 : Designing for Sustainability



GlossaryAbutment: the point of junction where the roof slopemeets a vertical surface or intrusion (e.g chimney or wall)

Arris hip tile: a purpose made tile, used with plain tiles,which ‘wraps’ around a hip

Attic: a storey of a house entirely in the roof

Bargeboard: a board, often covered or decorated.attached along the eaves of a roof in front of a gable.

Bonnet hip: a rounded hip tile used with plain tileswhich gives the appearance of a lady’s bonnet (known asa ‘granny’s bonnet’). The void beneath hip tiles is filledwith pointed mortar

Boxed eaves: eaves in which the members are concealedby simple woodwork

Brace: a timber, either curved or straight, placeddiagonally, to strengthen a frame, so as to form anapproximate triangle with two structural timbers

Capital: the crowning feature of a column

Cloaked or dry verge: tile used at the verge (gable)which wraps over the edge of the roof

Cogging: the laying of bricks diagonally in a decorativecourse eg cogged eaves

Collar: a horizontal timber tying together a pair ofrafters or principals, always above tie-beam level

Coping: construction or component at top of a wallthat is weathered and grooved, and overhangs the wallsurface below to throw water clear and provide protection

Corbel: a projection from a wall or reveal designed tosupport a weight

Cornice: the uppermost of the three main divisions ofthe Classical entablature. Often used in isolation above anopening. An eaves cornice is a moulding masking the eaves

Coupled: rafters joined by collars

Creasing tile: a flat tile without nibs for decorativefeatures for walls and window sills

Cresting: ornamental finish, or decoration, standingabove a horizontal feature such as the ridge of a roof

Cross wing: a range joined to the main range but with itsroof running at right angles

Crown post: a form of king post, in that it standscentrally on a tie beam, but to support a collar purlin andgenerally braced also to one of the collars

Cruck: A curved timber joined with another to make atruss, by which the roof is directly supported from a pointno higher than midway up the wall

Cupola: a small dome or domical roof

Decorative hips: a hip tile available in a variety ofshaped crests

Decorative ridge: a ridge tile available in a variety ofshaped crests

Dentil: one of a row of small blocks in the mouldingabove the frieze of a classical entablature

Dormer window: a window partly or wholly above theeaves, but vertical and thus breaking the roof-line

Double-camber: a tile arched both horizontally andvertically

Eaves: the overhanging horizontal, lower edge of the roof

Eaves (or Top) Tiles: short tiles used in a single course togive a double course of tiling at the eaves (or ridge)

Eaves soffit: boarding placed under spreading eaves toconceal the rafters or sprockets

Entablature: the horizontal part of a Classical ordercarried by the columns, and consisting of architrave,frieze and cornice

Eyebrow dormer: a very low dormer over which themain roof lifts and falls without a break

Finial: a terminal feature, e.g. at the end ridge of a gableand with some form of decoration on it, e.g. a scroll, balltop or fleur-de-lys

Flaunching: a mortar fillet designed to throw off waterat the junction where a masonry chimney stackpenetrates a roof

Froe: an axe-like tool used to split wood along the grain

Full dormer: one in which the entire window is abovethe eaves line, and the face of the dormer is flush withthe wall

Gable: triangular upper part of wall at end of a ridgedroof

Gablet: a small gable which stands above one of thepitched sections of a hipped roof and continues to theridge or similar feature, breaking one of the longerpitches of a roof

Gauge: the distance between two roof battens

Half dormer: only partly projecting into the eaves, butwith the window partly above the eaves line

Half hip: the hipped pitch begins halfway up the gable

Hip: the junction of two inclined surfaces which meet atan external angle

Interlocking tile: a single lap tile that connects withadjoining tiles by means of close fitting ribs

ChilternsRoofingMaterials 47



48

King post: a post which stands centrally on a tie beamor collar and directly supports the ridge piece

Kneeler: the base stone of a gable, projecting out fromthe wall and supporting the coping

Laced: method of weaving together adjacent tiles to turna roof angle

Lap: the amount by which one tile covers part ofanother

Ligger: A length of roundwood (usually hazel or willow),often split, laid over the upper surface of a thatch to holdin the eaves and barges of a long straw roof

Mansard roof: one with a steeper pitch and a shallowerupper pitch on each side

Mathematical tiles: hanging vertical tiles which givesthe appearance of brick cladding

Mitred hip: an abutment of two tiles at the hip

Modillion: a small moulded bracket in the cornice

Pantile: a single lap tile moulded to an S-shape whichgives the appearance of ‘waves’ and ‘troughs’ on the roof

Parapet: a low wall at the top of a wall, i.e. beyond theeaves line (which the parapet conceals)

Peg tile: a tile similar to a plain tile butwithout nibs and with holes for pegs

Plain tile: small roofing tile (265mm x165mm) cambered and having no otherfeature except nibs/nail holes

Plate: the timber into which the feet ofthe rafters are framed

Principal: one of the rafters of a largersection in a roof which supports thepurlins and is framed into the tie beam

Purlin: a longitudinal member in a roof below the ridgepiece and above the wall-plate

Queen post: one of two uprights, rising from a tie beamto support a collar

Rafter: one of the sloping timbers in a roof whichdirectly supports the covering

Raking dormer: a window above the eaves with a roofpitched in the same direction as, but shallower than, themain roof

Rainwater head: the hopper, sometimes ornamented,at the junction of a gutter and downpipe

Ridge: the horizontal apex of two slopes on a pitchedroof. In tiling, a single course of short tiles is used bothsides of the ridge

Ridge tile: tile covering the apex

Roman tiles: half-round overs and unders (true roman);half round overs and flat unders (single Roman); twin halfround overs and flat unders (double Roman)

Scantle slate: slates laid in diminishing courses

Single-camber: a traditional plain tile, arched along itslength from head to tail

Soaker: metal formed as a side cover piece to extendover a roof covering and overflashed so as toweatherproof the perimeter of roof penetrations orprojections

Spire: a tall pyramidal roof

Sprocket: a small timber attached to the rafter toprolong, or reduce the pitch of the eaves

Stack: the structure of masonry appearing on theexterior of a building and acting as a funnel to carrysmoke from a fire out of a building

Sun pipe: domed tube that sits on the roof surface witha reflective connecting pipe allowing light to be directedto a room below

Swept eaves: those which project at an angle rathershallower than the main pitch of the roof, beingsupported on sprockets

Swept valley: one formed by curved slating, tiling orstone rather than by a lead or zinc flashing

Tie beam: structural member passing across a building atthe level where the roof structure begins and into whichthe feet of the principals (if any) are tenoned into

Tile and a half (Gable tile): a tile one and a half timesthe width of a standard plain tile to maintain a brokenbond at verges and abutments. Sometimes called a gabletile

Tingle: a bent metal strip of lead, zinc, copper oraluminium, approx 2" long, used to reposition a slatesecurely. The strip is nailed to the batten below the slateto be replaced and then turned back as a stirrup to securethe slate

Torched: process of applying mortar to in situ tiles togive added security against the weather. ‘Single torching’consists of pointing the head of each tile from the insideof the roof. In ‘full torching’ the vertical joints betweenadjacent tiles are also pointed

Truss: the triangular figure formed by a tie beam and thetwo principals

Valley: the junction of two inclined roof slopes whichmeet at an internal angle, lined with lead or special valleytiles

Verge: the edge of the tiles projecting over the gable

Vertical tiling: general term applied to plain tiles fixedto walls to form a wall cladding, often known as “tile-hanging”


Bands picked out indarker tiles (Aldbury)



49

Bibliography Further AdviceFor any new development proposal you shouldinitially contact a Development Control PlanningOfficer in the Planning Department at your localcouncil. Additionally, if your proposal involves alisted building or is in a Conservation Area, youshould contact a Conservation/Listed BuildingsOfficer. You will also need to contact your LocalBuilding Control Service.

Details of all the councils that cover the ChilternsAONB can be obtained from the ChilternsAONBOffice.

The office will also be able to provide details ofsuppliers, practitioners and other useful contacts.This list may change from time to time, so it isrecommended that you check it regularly if youundertake projects at different times.

For further information and advice contact theChilterns Conservation Board at the followingaddress:

Chilterns AONB OfficeThe Lodge 90 Station RoadChinnor Oxon. OX39 4HA

Email: [email protected]:www.chilternsaonb.org

Ashurst, J. and N., Metals, Vol. 4, English HeritageTechnical Handbook, Practical Building Conservation,1988

Bennett, F. and Pinion A., Roof Slating and Tiling,1948, reissued (Donhead), 2000

Brockett, P. and Wright, A. The Care and Repair ofThatched Roofs (SPAB) Technical Pamphlet No 10,London, 1989.

British Standards Institution, Clay roofing tiles fordiscontinuous laying. Products, definitions andspecifications. British Standard BS EN 1304: 1998.London, BSI, 1998

British Standards Institution, Code of practice forslating and tiling. British Standard BS 5534: Part 1:1997 and Part 2: 1986. London, BSI, 1997 and 1986.

Chilterns Conference, Chiltern Buildings Design Guide,A Countryside Design Summary, 1999

Chilterns Conservation Board, Chilterns BuildingsDesign Guide, Chilterns Flint: SupplementaryTechnical Note, 2003

Chilterns Conservation Board, Chilterns BuildingsDesign Guide, Chilterns Brick: SupplementaryTechnical Note, 2006

Clay Roof Tile Council, PlainTiling Guide (ND).Availableon CRTC website, seewww.clayroof.co.uk

Clay Roof Tile Council,Vertical Tiling Guide (ND).Available on CRTC website

Dobson, C.G., Roof Tiling, 1931

East Herts District Council Tiles and Slates HistoricBuildings and Conservation Areas: Guidance Notes,(ND)

English Heritage, Thatch and thatching: a guidancenote, 2000

Fearn, Jacqueline, Thatch and Thatching ShireAlbum,Reprinted 2005

Harrison, H.W., Roofs and roofing BRE Buildingelements, 2000

Hertfordshire County Council Tiles and Slates inHertfordshire Hertfordshire Conservation File/Information and Advice 3 (ND)

HSE, Safety in roofwork (Guidance Booklet HS(G)33)

Hutson, A. M., Bats in Houses, Bat ConservationTrust, 1993 (ISBN 1872745105)

Lead Sheet Association The Lead Sheet ManualVol 1: Lead Sheet Flashings 1990Vol 2 Lead Sheet Roofing 1992Vol 3 Lead Sheet Weatherings

Lemmen, H. Van, Ceramic Roofware, Shire Album 420

Moir J., and Letts, J., Thatch: Thatching in England1790-1940. English Heritage Research Transactions:

Research and Case Studies inArchitectural Conservation,5, 1999

Williams, G.B.P, Chimneysin Old Buildings (SPAB)Technical Pamphlet No 3,London 1971.

(Berkhamsted,Photo by E. Sumner )


Tel: 01844355500 Fax: 01844355501


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Chilterns Area of Outstanding Natural Beauty · note.Adherence to the guidelines does not mean that development proposals will necessarily be approved because other planning policies