Building Regulations and Historic Buildings 2002 - English Heritage

8/8/2019 Building Regulations and Historic Buildings 2002 - English Heritage

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Building Regulations andHistoric Buildings Balancing the needs for energy conservation with those of buildingconservation: an Interim Guidance N ote on the application of Part L


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Summary

English Heritage supports the Governments aims to improve energy efficiency,provided that the application of the new Part L is exercised in a way that doesnot harm the special interest of historic buildings. A sensible and reasonableapproach should achieve improvements in most cases, although not always tothe standards recommended in the Approved Document.

The new Part L makes it clear that the special characteristics of a historicbuilding must be recognised.The aim of this revised part of the BuildingRegulations is to improve energy efficiency where practically possible, providedthat this does not harm the character of the building or increase the risk oflong-term deterioration to fabric or fittings.

The special interest of a historic building would be compromised if its overallappearance were to be changed or significant features or qualities were to be

lost as a result of compliance with the Requirements of the new Part L.To averta threat of this kind, a number of questions need to be considered. Couldimprovements be made without the need to remove or substantially alterfabric?For example, could existing windows be repaired and draughtproofed asan alternative to inserting new double glazing?Could secondary glazing beinserted?If improvements to the existing windows are not practicable, couldbenign improvements be made elsewhere, for example by insulating underfloors or by improving the efficiency of the heating system?

An understanding of what constitutes the special interest of a historic buildingrequires experience. Early consultation with a conservation officer is thereforestrongly recommended.

Interim Guidance Note

Building Regulations 2000 (2002 edn):

Section 2

Table: cross-references from the to the appropriat e sections in PartL1 of the Approved Document to the Building Regulations 2000 (2002 edition)

English Heritage: Interim Guidance Note Part L1 Approved Document

1 Preface2 The context of the revisions to Part L

3 Histor ic buildings definit ions and statutor y protection Page 11, 0.19: Page 21, 2.9

4 Principles of repair and alteration to histor ic buildings5 Specific reference to historic buildings in Part L Page 11, 0.19

6 Meeting the Requirements of Part L Page 7, 1.11 1.14: Page 18, 1.58 1.62(Improving energy efficiency in historic buildings)

7 Historic buildings as environmental systems Page 12, 1.3 1.35

8 Windows Page 19, 2.3 a,Table 1 and Sections A1,A2 and A3

9 Doors Page 19, 2.3 a,Table 1 and Sections A1,A2 and A3

10 Walls Pages 20, 21, 2.6 c, 2.8 d

11 Floor s Pages 20, 21, 2.6 b, 2.8 c12 Roofs Pages 20, 21, 2.6 a, 2.8 b

13 Building Services Pages 15 18, 1.36 1.57: Page 12, 1.7:Page 19, 2.3 (b f): Page 21, 2.8 f and g

Contents

Summary 2

Glossary 2

1 Preface 3

2 The context of the revisionsto Part L 4

3 Historic building definitions and statutor y protection 5

4 Principles of repair and alterationto histor ic buildings 6

5 Specific references to historic buildings in Part L 6

6 Meeting the Requirements of

Part L 8

7 Historic buildings as environmental systems 9

8 Windows 12

9 Doors 16

10 Walls 16

11 Floors 17

12 Roofs 17

13 Building services 19

14 Forthcoming advice 20

References21

Acknowledgements and attributions 22

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Glossary

Conservation Area Conse nt T his isrequired from the local planning authority forthe demolition of an unlisted building in aconservation area [Section 74 (1) of the Townand C ountry P lanning (Listed Buildings andConservation Areas) Act 1990). T here arehowever several exemptions where differentconsents are required, for example, listed andecclesiastical buildings and scheduled ancientmonuments.

Conservation O fficer A heritageconservation specialist referred to in PlanningPolicy Guidance Note 15 (PPG 15, 1994),often a member of the Institute of HistoricBuilding C onservation ( IHBC ), responsiblefor technical and other advice within a localplanning authority. Local authorities whichadopt a team-based approach sometimes

delegate responsibilities for historic buildings,in the first instance, to a nominated planningofficer within the development controlsection. For the p urposes of this InterimGuidance Note , the term conservation officerrefers to both classes of staff, and/or specialistconsultants.

DEFRA Department of the Environment,Food, and Rural Affairs

DETR Department of the Environment,Transport and the Regions

DNH Department of National HeritageDoE Department of the Env ironment DTLR Department for Transport, Local

Government and the Regions(Building Regulations Division was part of DT LR until 20 June 2002, after which itbecame the responsibility of the Office of theDeputy Prime Minister.)

Listed Building Consent Listed BuildingConsent is needed for the demolition of alisted building, or for its alteration orextension in any manner that would affect its

character. Listed Building Consent shouldnormally be obtained before BuildingRegulations approval is sought. Carrying outunauthorised works on a listed building is acriminal offence [Planning (Listed Buildingsand Conservation Areas) Act 1990 Sections79]. Planning Policy G uidance N ote 15(PP G 15) p rovides detailed advice andguidance for those making or consideringapplications for Listed Building Consent.

Listed buildings: gradings Buildings aregraded to show their relative architectural orhistoric interest:

Grade I buildings are of exceptional interestG rade II* are particularly importantbuildings of more than special interestGrade II are of special interest, warrantingevery effort to preserve them

Sarkings Roof underlinings of board, and/orbituminous felt or modern buildingmembranes, fixed beneath slates or tiles

Scheduled Ancient Monuments and theBuilding Regulations Scheduled AncientMonu ments are not subject to the BuildingRegulations, including Part L. Works carriedout to a building which is included in theschedule of monum ents maintained undersection 1 of the Ancient Monum ents and

Archaeological Areas Act 1979 are exemptfrom the Building Regulations 2000. (Section3 of the Building Act 1984 and Regulation 9,schedule 2, class 1, of the Regulations refer.)

The U-value T hermal transmittance (i.e. theU-value) is a measure of how much heat willpass through one square metre of a stru cturewhen the air temperatures on either sidediffer by one degree. U-values are expressedin units of Watts per square metre per degreeof temperature difference (W/m 2 deg C). [SeeDT LR 2001, Section 0.]

1 Preface

1.1 For whom is this guidanceintended?It is offered to those responsible foroverseeing the implementation of the October2001 edition of Building RegulationsApproved Document Part L, Conservation of Fuel and Power (D T LR, 2001) where itaffects historic bu ildings. ApprovedDocument Part L came into force on 1 April2002.

T his document is intend ed for the following:building control officersapproved inspectorsconservation officersenvironmental health officershousing officers

T he guidance will also be of interest to

designers and others who are prepar ingproposals for work on historic buildings.

1.2 W hat is its purpose?T he Interim Guidance N ote has beenproduced to help prevent conflicts betweenenergy conservation policies enshrined in therevised Building Regulations and policiesconcerned with planning and theconservation of the historic environment.

1.3 Balancing conservation interests

English Heritage and other buildingconservation bodies support the aim of conserving fuel and power provided that itdoes not compromise the special interest,character and appearance of historicbuildings. T he right balance is neededbetween reducing energy use and greenhousegas emissions, and conserving the nationaland local heritage. T his is broad ly in line withsound sustainability principles subscribed tonationally and developed locally through theAgenda 21 p rogramme.

1.4 Sustainability In environment terms, the continued use of existing building stock.coupled with measuresto improve energy efficiency is a global priority(BS 7913: 1998). Replacing an existingbuilding with a new one requires aconsiderable investment of embodied energyin materials, transport and construction typically equivalent to five or ten years of

building. In global environmental terms, thebalance of advantage strongly favours the

retention of existing building stock, particularlywhen performance in terms of energyconsumption in use can be improved (BS 7913:1998). Retaining existing elements of construction in old buildings and seeking to

Box 1 Building Regulations RequirementsThe Requirements of the revised Regulations are (for the most part) written in functional terms andonly adequacy is required; in some cases a nil provision may be judged to provide it. Only in the rarecases when a Requirement is expressed in prescriptive terms could a relaxation be needed.TheApproved Documents of course are entirely for practical guidance none is mandatory. Unfortunatelythere is a belief (still shared by some architects and local authorities) that where the guidance is notfollowed some kind of approval is required.This is not so.

energy use to heat, light and condition the

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enhance their thermal p erformance in benign 1.6 Energy conservation measures within this heritage stock. However, specialways, rather than replacing them, is a heritage T hese measures should not be app lied care and a flexible approach are needed soconservation princip le in line with this without due regard to the special that the interests of historic buildings can beconcep t of sustainability. character istics of a historic building. In preserved.

plan into local policy and action.

Box 2 Local Agenda 21Sustainable Development is defined asdevelopment that meets the needs of thepresent without compromising the ability of

future generations to meet their own needs(The Brundtland Report, United Nations WorldCommission on Environment and Development,1987). It is not just about environmentalprotection.To succeed it needs to embrace allthe three Es Economics, Equity, and Environment.

At the Rio Earth Summit in 1992, the worldsleaders formulated a plan or Agenda for the21st century, which was taken up enthusiasticallyat a local level in England, and internationally, asLocal Agenda 21.

This is the sustainable development initiative onwhich local authorities and communities havebeen working for a decade to turn the global

1.5 The appropriateness of improvingenergy conservation in historicbuildingsDuring the development of the revisions toPart L , discussions with the D epartment forTransport, Local Government and the

Regions (D T LR, formerly the D epartment of the Environment, Transpor t and the Regions[DET R]) gave rise to thoughts of seeking thecomplete exemption of listed buildings fromonerous energy conservation improvementslikely to prove detrimental to their specialinterest. Cer tainly some historic buildingsshould not be altered at all, e.g. those whereany change would inevitably damage theircharacter or special interest (Staniforth andHayes 1989). However, the majority canaccommodate some improvements, eventhough the modern standards and techniquessuggested in Part L might not be app ropriate.

Box 3 Reasonable provisionAs stated in the introductions to Parts L1 andL2, Approved Documents are intended toprovide guidance for some of the morecommon building situations there is noobligation to adopt any particular solution ifyou prefer to meet the relevant Requirement insome other way. DTLR therefore decided thatwhat constituted reasonable provision theRequirement of the Statutory Instrument wasbest established for each historic building on itsparticular merits. (The Requirements themselvesare framed in very general terms, for exampleReasonable provision shall be made for theconservation of fuel and power by limiting theheat loss through the fabric of the building.)

particular, D T LR r ecognises thatimprovements to the building envelope, andespecially thermal insulation, can beparticularly difficult for architecturally orhistorically important buildings. Alterationsare often impossible at least to someelements without unacceptable damage tothe historic fabric or cultural record, or thecreation of uncertain technical risks, e.g.exacerbating risks of decay in timber.Similarly, opportunities for energy savingshould not be missed just because a buildingis of historic or architectural interest.(Research has shown that improvements inthe thermal insulation of buildings can causeproblems in other areas. Designed to supportthe latest Building Regulations for the

conservation of fuel and power, the reportT hermal insulation: avoiding risks [Stirling2002] explains the hazards involved inmeeting Requirements when thermallyinsulating roof, walls, windows and floors.)

1.7 The advantage of earlyconsultationAn early dialogue between the buildingcontrol and the conservation officers in thelocal planning author ity is encouraged. T his isalready standard practice in some authorities

which have adopted a development teamapproach (D ET R, 1998) to give a singlepoint of advice to applicants.

2 The context of the revisionsto Part L

2.1 The need to reduce greenhousegas emissionsT he Government is committed to reducingglobal warming by reducing the emissions of greenhouse gases. T he UK has set a target of reducing emissions of the most importan tgreenhouse gas, carbon dioxide (C O 2) by 20per cent on 1990 UK emissions. T he targetyear is 2010. Operational energy in buildings burning fossil fuels to provide energy forheating, ventilation, lighting etc. accountsfor 46 per cent of the U Ks CO 2 emissions.Since new construction amounts t o onlyabout 1 per cent of the stock per year,emissions from existing buildings cannot beignored, and need to be generally reduced, if policy aims are to be met. Historic buildings

constitute less than 6 per cent of the totalbuilding stock of England, and are a preciousfinite resource. English Heritage believes thata contribution towards national energyconservation requirements can be m ade from

2.2 Extending Building Regulations toexisting buildingsDT LRs amendments to ApprovedDocum ent Part L of the Building Regulationscame into force on 1 April 2002. T hey seek toimprove the energy performance of allbuildings, including existing ones, whenaltered, extended or subjected to a change of use. Before this, approval was required only if the works affected structural safety, fire safety,and access for disabled people. Now most modifications to a building require consent,and reasonable provision needs to be madefor the conservation of fuel and power.

2.3 The purpose of this Interim

Guidance Note Du ring the consultation stage of Part L,English Heritage liaised closely with D T LR informulating the revised regulations tosafeguard the interests of historic buildings.It was agreed that English Heritage with thesupport of DT LR would prepare an InterimGuidance Note to assist building controlbodies when assessing applications dealingwith historic buildings where theRequirements for Part L need to be satisfied.This Note sets out the principles that need to

be considered when alterations arecontemplated to historic buildings. It focuseson dwellings (Approved Document Part L1),but is equally applicable to non-domesticbuildings (Approved Document Part L2).

2.4 Guidance on the application ofthe Building Regulations to historicbuildings (especially on liaison between building control and planning teams at local level)English Heritage is collaborating on thedevelopment and p roduction of a ProceduralGuide (in p reparation, 2002) for localauthorities on the m ethods to be adoptedwhen building control bodies apply theBuilding Regulations to historic buildings.T his further guide will highlight, from localauthority good practice, the circumstances inwhich the advice of conservation officers inplanning departments should be sought andused. T he guide will recommend that, toavoid problems, liaison must start at theearliest stages of the project, well in advanceof the formal control processes.

2.5 Next stepsT his current Interim Guidance N ote has beenprepared to coincide with the early monthsduring which the revised regulations came

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into force (the Spr ing of 2002). It is hopedthat further research will be commissioned byEnglish Heritage later in 2002 to provideadditional technical material for a morecomprehensive docum ent. T his is intended tosupersede the Interim Guidance N ote at a dateto be announced in the following year. It willinclude:

generic methods for improving energy

efficiency in ways that help to avoidharming the important features andqualities of historic buildingstechnical information on traditionalmaterialsillustrated details and case studies.

3 H istoric building definitionsand statutory protection

3.1 Definitions used in Part LParagraph 2.9 of Part L1 and Paragraph 4.10of Part L2 identify the following as historicbuildings:

a) listed buildingsb) buildings situated in conservation areasc) buildings which are of local architectural or

historical interest and which are referred to asa material consideration in a local authoritysdevelopment plan

d) buildings of architectural and historicalinterest within national parks, areas of

outstanding natural beauty, and world heritagesites.

Statutory issues affecting buildings in eachof these four categories are outlined below.A conservation officer should be consultedbefore modifications are undertaken tobuildings in any of these categories. Manybuildings of architectural, townscape,landscape or historic interest do not fall intoany of these specific categories but alsorequire sensitive consideration.

3.2 Listed buildingsListed buildings are those included on thestatutory List of Buildings of SpecialArchitectural or Historic Interest. Controlsapply and L isted Building Consent isrequired for any works of alteration orextension both external and internal which would affect a buildings character.Fixtures and curtilage buildings i.e. anyobjects or structures which are fixed to thebuilding, or are within the curtilage (and havebeen so since before July 1948) are treated

as part of the listed building. T he samecontrols apply whatever grade of listing thebuilding is given.

T he Governm ents policies on the

conservation of listed buildings are enshrinedin PPG 15 (D NH and D oE, 1994). Workswhich materially and detrimentally affect thespecial architectural or historic interest of thelisted building should not receive the benefitof consent. Paragraph 3.26 advises that theBuilding Regulations should be operated in away which avoids removal of features whichcontribute to the character of a listedbuilding, and authorities should consult theirown conservation officers, or seek expertadvice from other sources, when handlingdifficult situations.

3.3 Buildings in conservation areasConservation areas are any areas of specialarchitectural or historic interest, the characteror appearance of which it is desirable topreserve or enhance. Conservation Areadesignation encourages authorities toimplement conservation policies over these

sensitive areas.

In a conservation area, the main emphasis ison external appearance, with surface materials(walls and roofs) and the details of windows,doors, and rooflights being extremelyimportant. C hanges to these may needplanning permission, especially if they aresubject to an Article 4 direction (see Box 4)under the Town and C ountry P lanning Acts.Consent is also needed for the demolition of most buildings in a conservation area.

Consent is not needed for internal alterationsto unlisted buildings. While not all buildingsin a conservation area will be of historicinterest, many are: original internal andexternal features contribute to the impor tanceof these and therefore have a direct impact onthe character of the area.

3.4 Buildings of local architectural orhistoric interest referred to in a localauthoritys development planT his category includes a local authorityslocal list or supplementary list of historicbuildings, which has been included in theirunitary or local plan (known as thedevelopment plan). Inclusion within the planmeans that any list of this kind has beensubject to public consultation and is amaterial planning consideration in thedetermination of applications under theTown and C ountry P lanning Acts.

Most buildings on these lists are goodexamples of a particular design or style of

construction, e.g. buildings of the Arts andCrafts movement of the late 19th and early20th centuries, the work of a noted localarchitect, or a building associated with a localhistorical figure. They cou ld well become the

listed buildings of the future.

T hese buildings have no statutor y protectionunless they are within a conservation area.Nonetheless, if they are to retain theirimportance it is often essential that originalfeatures and fabric are preserved in anyschemes of alteration or extension.

3.5 Buildings within National Parks,Areas of Outstanding Natural Beauty,and World Heritage SitesBuildings often help to create the townscapeand landscape qualities which were amongstthe original reasons why an area or a siteachieved its designation. T hey use localmaterials and highlight vernacular traditions.Elements such as roofs, windows, rooflightsand doors typify their period, age and style.While these designated areas do provideslightly more control over permitted

developments than elsewhere, manyimportant features on unlisted buildings arenot safeguarded, and improvements to energyefficiency must avoid harming them.(Other buildings in these areas may berelatively modern or much altered, andmay accommodate energy-saving featuresmore easily.)

1995

non-listed building.

Box 4 The Town and Country Planning(General Permit ted D evelopment) Order

Article 3 of this Order grants planningpermission for various classes of developmentwhich are set out in schedule 2 of the Order.These are known as permitted developmentand include, for example, replacing windows in a

An Article 4 direction may be made by aLocal Planning Authority or by the Secretary ofState where either is satisfied that it isexpedient that the permitted development(with some exceptions) should not be carriedout unless permission is granted for it onapplication. If in Article 4 dir ection was in place

and included windows, then an application forplanning permission would be needed forreplacements.

3.6 Other buildingsOther buildings may fall outside any of thecategories above, but have historic andarchitectural features for the preservation of which a sound case can be made. T heseinclude:

buildings in historic parks and gardensbuildings in the curtilages of Scheduled Ancient Monumentsbuildings or groups with distinguishinglocal or architectural characteristics whichare often regarded as commonp lace until

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they vanish. For example, in recent yearsinappropriate window replacements havetaken their toll on many previouslyharmonious and well-proportionedvernacular buildings.

If in any doubt, consult a conservation officer(or a nominated officer).

4 Principles of repair andalteration to historicbuildings

4.1 The sensitivity of historic buildingsA historic building in its townscape orlandscape setting, complete with its interiordecoration, fixtures and fittings, can beregarded as a composite work of art anddocument of history. Historic buildings varygreatly in the extent to which they can

accommodate change without loss of theirspecial interest. Some are sensitive to evenslight a lterations, par ticularly externally, andwhere they retain important interiors, fixtures,fittings and details. Others may have changedsignificantly and restoration is not consideredfeasible or sensible. T hese considerations willinfluence the extent of change that isappropriate to improve energy efficiency.

4.2 Principles outlined in Part LParts L1 and L2 state: T he need to conserve the

special characteristics of historic buildingsneeds to be recognised the aim should be to

a

Figure 1 (a, above) Double glazing in PVCu cannot replicate theappearance of an original timber sash with fine glazing bars.(b, right) An unfor tunate combination on the same faade:original timber sashes (ground floor), PVCu replacements (firstfloor) ( Photographs: Chris Wood and English Heritage Building Conservation and Research Team )

improve energy efficiency where and to the extent that it is practically possible, always provided that the work does not prejudice the character of the historic building, or increase the risk of long-term deterioration to the building fabric or

fittings. In arriving at an appropriate balancebetween historic building conservation and energy conservation, it would be appropriate totake into account the advice of the local planningauthoritys conservation officer.

4.3 Identifying the special elementsBefore considering any alteration, it isessential to assess the elements that make upthe special character and interest of thebuilding, including:

External features such as a decorativefaade, windows and doorsT he spaces and internal layout T he planof a building is one of its most importantcharacteristics. Interior plans should be

respected and left unaltered as far aspossible.

Internal features of interest such asdecorated plaster surfaces, panelling, floors,window shutters, doors and doorcases

Details such as mouldings, stucco-work,wall and ceiling decorations can be justas valuable in simple vernacular andfunctional buildings as in granderarchitecture, and can be a buildingsmost important features.

Besides the historical or aesthetic importanceof a building and its fixtures, the

archaeological or technological interest of thesurviving structure and surfaces may also besignificant.

4.4 Principles of minimuminterventionA traditional building needs to be consideredas a whole and treated in a holistic way.Its structure, materials and methods of construction and p atterns of air and moisturemovement should be properly understood.A fundamental principle is to minimiseintervention. The stock of historic buildings isfinite and every loss or major alteration tofabric is significant. Therefore a con servativeapproach is needed with knowledge andexperience to d etermine what is impor tantand how changes can be made with the leasteffect on the character of the building.

4.5 Principles of repairWhere new work can be carried out withminimal effect on historic fabric, it should becarefully matched and blended with the old inorder to achieve an architectural whole. Asmuch old work as possible should be retainedand recorded ( Clark, 2001). New materialsintroduced in the course of like-for-like worksshould match the original materials as closely aspossible. T he detailing of the new work shouldmatch the original or existing work exactly.

4.6 Principles of alteration

When alterations for energy conservation areproposed, regard should be given to:

b

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ensuring that the building is wellunderstood, to avoid damageminimising disturbance to existing fabricreversing the changes easily withoutdamaging the existing fabric (especially changes to services)appreciating that some buildings or parts ofbuildings are of such quality, importance orcompleteness that they should not bealtered at all save in the most exceptionalcircumstances.

BS 7913:1998 expands on these principles.

4.7 Understanding how the buildingworksMany historic buildings include soft, weak orpermeable materials, e.g. mortars, plasters,renders and paints. T hese cause the fabric torespond in fundamentally different ways toair, moisture and structural movement from

the hard, strong, impervious materials andmembranes widely used in m odernconstruction. Before any work is carried out,it is therefore important that a buildingssystem of construction and the way in whichthis might have changed over time isunderstood an d that alterations arecompatible with this system.

4.8 Introducing modern materialsTo use modern substitutes and to introduceimpermeable materials or membranes into

permeable traditional construction is usuallynot good p ractice and can lead to troub le.Obvious examples include the use of cementitious mixes for plasters, renders andpointing where, for example, incompatibilitiesin flexural strength, permeability and porositycan lead to disastrous salt migration anddamage. As a general rule materials andtechniques designed for new constructionshould be treated with caution and if possibleavoided, as their long term or side effects on abuilding or its occupants are not fullyunderstood. That said, some n ew synthetic ornatural materials used thoughtfully andskilfully, e.g. for perm eable insulation, canfacilitate the most conservative andeconomical work.

5 Specific references tohistoric buildings in Part L

5.1 IntroductionAs outlined above, the Part L revisions:

appreciate that historic buildings requiredifferent approaches from m odern onesrecognise the potential conflicts betweenbuilding and energy conservation and seek to mitigate them by taking a flexibleapproach

allow what is reasonable to be determinedin relation to each buildings specialcharacteristics.

T his Section examines specific issues raised.

5.2 W hat tr iggers the Part LRequirements?

For existing buildings, Part L generallyrequires energy conservation upgrading onlyfor elements which are to be substantiallyreplaced as part of the works. T heRequirements do not ap ply to normal repairand patching work. While a material changeof use could trigger wider-ranging upgrades,Part L states that consideration would be onindividual merits and would need to takeaccount of historic value.

5.3 Deter mining the specialcharacteristics

Advice on the factors determining the character of historic buildings is set out in PPG 15 (L1,paragraph 0.19; L2, paragraph 0.24).

To determine the special characteristicsrequires knowledge and experience. Advicefrom the conservation officer should usuallybe sought, not only to identify which parts of

the structure are original or of historical orarchitectural importance, but also thesignificance of layout, plan-form and spaces.

5.4 Specific guidance in Parts L1and L2Specific guidance is reproduced in Box 5.Paragraphs 2.9 and 2.10 have already beenreviewed in Sections 3 and 4 above.Paragraph 2.11 mentions circumstances inwhich it might be reasonable to reverseprevious interventions, to replace features inthe original manner, or to improve moisturecontrol, even if this were to reduce energyperformance. For example, it might bepermissible to:

replace inappropriate double glazing withsingle-glazed windows which match theoriginalsrelax the strict interpretation of Part L forworks of reconstruction and infill wherethis would prejudice the creation of anappropriate facsimileallow the fabric to breathe in spite of theextra heat loss which may occur throughreduced insulation and/or higher ventilationrates. T his is discussed fur ther in Section 7of this Interim Guidance N ote.

2.9 Historic buildings include

1

2.

1

2

Box 5 Sections 2.9 2.11 of Part L1(Note: apart from some numbering, Section 4 of Part L2 is identical to the content of this box)

a) listed buildings,b) buildings situated in conservation areas,c) buildings which are of architectural and histor ical interest and which are referred to as a

material consideration in a local authoritys development plan,d) buildings of architectural and histor ical interest within national parks, areas of outstanding

natural beauty, and world heritage sites.

2.10 The need to conserve the special characteristics of such histor ic buildings needs to berecognised . In such work, the aim should be to improve energy efficiency where and to theextent that it is practically possible, always provided that the work does not prejudice thecharacter of the historic building, or increase the risk of long-term deterioration to the buildingfabric or fit tings. In arriving at an appropriate balance between histor ic building conservation

and energy conservation, it would be appropriate to take into account the advice of the localplanning authoritys conservation officer.

2.11 Particular issues relating to work in historic buildings that warrant sympathetic treatment andwhere advice from others could therefore be beneficial include a) r estor ing the histor ic character of a building that had been subject to previous inappropriate

alteration, e.g. replacement windows, doors and rooflights;b) rebuilding a former historic building (e.g. following a fire or filling in a gap site in a terr ace);c) making provisions enabling the fabric of histor ic buildings to breathe to control moisture

and potential long term decay problems

BS 7913: 1998 Guide to the principles of the conservation of historic buildings provides guidance on

the principles that should be applied when proposing work on historic buildings.Hughes, 1986 The need for old buildings to breathe

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(Digital

BASEMENT GROUND FLOOR FIRST FLOOR

MEZZANINE

Figure 2 The layout, plan form andspaces are vital features of historicbuildings and need to be understoodbefore changes are proposed.image by Ray Martin from English Heritage original)

6 Meeting the Requirementsof Part L

6.1 IntroductionBetter energy efficiency can be achieved byphysical change to the building fabric andservices and/or by more mindful behaviour byoccupants. Building Regulations tend toinfluence only the physical changes thoughthey can facilitate better behaviour, forexample by improving controls and usabilityand (in the current revisions to Part L) bybeginning to require better sub-metering,commissioning records and log books forheating and cooling systems, and power and

lighting.

6.2 The Statutory Requirements T he Requ irements for dwellings include items Items (e) and (f) apply to buildings with aT he Statutory Requirements for non- (a)(d) and (h), which apply only to heating floor area greater than 200 sq m and (g) todomestic buildings are summ arised in Box 6. and hot water services for domestic buildings. those with a floor area over 100 sq m.

(i)

conditioning systems

Box 6 The Statutory Requirements (Source: Part L2 of the Approved Document, page 8)

L2. Reasonable provision shall be made for the conservation of fuel and power in buildings or parts of

buildings other than dwellings by(a) Limiting the heat losses and gains through the fabric of the building(b) Limiting the heat loss

from hot water pipes and hot air ducts used for space heating(ii) from hot water vessels and hot water service pipes

(c) Providing space heating and hot water systems which are energy-efficient(d) Limiting exposure to solar overheating(e) Making provision where air conditioning and mechanical ventilation systems are installed, so that no

more energy needs to be used than is reasonable in the circumstances(f) Limiting the heat gains by chilled water and refrigerant vessels and pipes and air ducts that serve air

(g) Providing lighting systems which are energy-efficient(h) Providing sufficient infor mation with the relevant services so that the building can be operated and

maintained in such a manner as to use no more energy than is reasonable in the circumstances

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6.3 Relevance of the StatutoryRequirements to historic buildings(a) Limiting the heat lossesthrough the fabric

caused by condu ction and air infiltrationis by far the most common area of conflict between building and energyconservation.

(b ) Limiting the heat loss from pipesandducts will not normally be aproblem, except where access is difficult,or the installations are of historic interestor part of the architectural character.

(c) Providing [energy-efficient] space heatingand hot water will occasionally causeproblems where historic equipment is tobe conserved or for example whereelectric systems are preferred to avoiddisruption t o surface finishes or fabriccaused by pipework or to limit the risk of flooding. High efficiency boilers maysometimes also be unacceptable where old

flues need to be kept warm and dry, orwhere the steam plume from acondensing boiler could be unsightly orcould put items in its path at greater risk of damp and decay.

(d ) Occasionally the need to limit solar heat gains may be a problem particularly insome 20th-century buildings of architectural interest but these will notbe dealt with here.

(e) Reasonable standards for air conditioningand mechanical ventilation

Air conditioning installed in historicbuildings may sometimes be less efficientthan in new buildings, owing torestrictions p laced on appearance, accessor space.

(f) Insulation to air ducts, chilled water and refrigerant pipes and vessels may sometimesbe restricted for appearances sake, orbecause of limited space.

(g) T he need for efficient lighting maysometimes conflict with a requirement forauthentic appearance: for example,creating the more traditional sparkle of tungsten filament lighting requires lessefficient light sources.

(h ) Good record information is just as valuablein historic as in new buildings.

6.4 The general approachT he following broad principles should beobserved when energy efficiency is beingimproved in a historic building:

do not undertake unnecessary changesdo not cause the physical or visual loss of important featuresavoid changes increasing the risk of damageelsewhere in the structure (advice may wellbe required from technical specialists andthe conservation officer).

A holistic evaluation should be undertaken of the buildings energy efficiency. For exam ple,while one element such as a single-glazedwindow may not be easily improved (exceptby concealed draughtproofing), anothersuch as a thatched roof or a thick masonrywall may be capable of exceeding therecommended U-value.

6.5 Applying Part L t o existingbuildings

For exis ting bu ildings, there is no Requirement in Part L to upgradeelem ents w hich do not need replacing.T he purp ose of Part L is not to forceunnecessary intervention, but t o make surethat when replacements and major alterationsare undertaken, the elements are up graded toan extent that is reasonable; and wherepracticable to the required standards for a

new building.

When deciding whether to repair or replace, itis essential to consider the implications of destroying existing fabric against the potentialbenefits. For example, it would be neithersustainable nor cost-effective to replace a200-year-old window that is capable of repairand upgrading with a double-glazedalternative, and even less so if the newwindow were to have an anticipated life of only 2030 years, as some do. However

depending on circumstances a good casemight be made for well-designed andcarefully-installed draughtproofing orsecondary glazing (see Figure 16).

Where p roposed alterations or replacementscould trigger the Part L R equirement toupgrade t he existing fabric, care must beexercised in deciding whether or not suchwork will affect the buildings character: of course, if the building is listed, ListedBuilding Consent may also be required. Insome instances, a historic building may be inan almost totally original state, and like-for-like replacement will be the only appropriatesolution. In many cases, however, somethermal upgrading will be practicable. Forexample, though wall insulation will often beinappropriate (see Section 10), it may befeasible to add insulation in roofs and undersuspended floors. Provided this does notintroduce technical risks (see Section 7), itmight even be reasonable for this insulation toexceed the recomm endations in Part L tohelp make up for shortcomings elsewhere.

6.6 Ventilation, airtightness andmoisture controlWhen work is carried out to windows orinsulation, the App roved D ocument for

Part L recommends reasonable sealingmeasures to ensure airtightness . T his tends tobe part of a build tight, ventilate rightstrategy, with ventilation rates recommendedfor modern buildings in Part F of theBuilding Regulations (DET R, 2000).However, this guidance is based primarily ondispersing moisture and pollutants generatedby the occupants in modern buildings, whicheffectively create a barrier to externalmoisture. Bu ildings with solid walls,permeable materials and no dam p-proof courses operate differently and may requiremore ventilation to ensure their welfare, andthe comfort of their occupants, as discussedin Section 7.

6.7 Applying Part L to extensions tohistoric buildingsAn extension will normally be able toaccommodate a higher standard of thermal

performance than the host building. Anexception would be where the extension wasdesigned to be a true facsimile of a previousstructure or where certain planningrequirements generated the need for elementsto complement the historic building in termsof construction and detailing.

Sometimes an extension, such as aconservatory, can improve the thermalperformance of the whole building, forexample by reducing heat loss through the

surface to which it is attached and enhancingsolar gain. However, care needs to be taken inthe design and integration of such structures:

If unheated and isolated (for example, bydoors which are usually kept closed inwinter), a conservatory will normally bewarmer than ou tside and reduce heat lossesfrom the building to which it is attached.However, if heated or unheated but leftopen to the adjacent building the wholebuildings heating requirements could besignificantly increased .

7 Historic buildings asenvironmental systems

7.1 IntroductionT his Section deals with issues that need to beconsidered in developing and reviewing anintegrated approach to a historic building.

At the large scale, the performance of thewhole building must be assessed in a

holistic approach to heating, ventilation,insulation and energy efficiency.

At the medium scale, it is necessary toreview how the conditions vary from placeto place around the building.

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At the smaller scale , it can be difficult andsometimes impossible to make satisfactory

junctions between different elements andconstruction details with different typesand levels of insulation, so these must becarefully examined.

If not properly integrated at all the scales,problems can arise in particularcondensation, mould and decay.

7.2 Technical risks identified in Part LPart L recognises that technical risks can arisein the application of energy conservationmeasures such as the increase of unwantedmoisture and harmful effects on health.Section 0 of Parts L1 and L2 refersspecifically to the following p ublications forguidance:

T hermal Insulation: Avoiding Risks (BREReport No 262: see Stirling 2002). This

discusses many potential problems, andconfirms that thermal insulation, heatingand ventilation must be consideredtogether.

Approved Documents parts F, J and E onventilation, combustion systems andacoustics. (Only the ventilation aspects arecovered in this Interim Guidance N ote .)

Robust Details (see DEFRA and DT LR,2001) Th is publication refers to m oderndomestic construction and therefore is notdirectly relevant to historic buildings.

However, it illustrates the technicalimplications of applying the principlesoutlined in Par t L and by Stirling (2002)and so may assist review and discussion of their relevance to conditions encountered ina historic building.

7.3 Risks associated with thermalupgradingT hermal Insulation: Avoiding Risks (Stirling2002) goes over many of the problems thatcan arise in new buildings or majoralterations. However, three generalrequirements in its first section often provedifficult or impossible to satisfy in historicbuildings:

Insulating the s tructure uniform ly, avoiding therm al bridging Problemsoften arise at the junctions betweendifferent elements and construction details.Ensuring continuity is often difficult, asdiscussed below.

Providing a well-controlled heating system , with heat emitters in roomswhere heat will not be gained from

heated s paces elsewhere T his is to helpreduce moisture levels and avoidcondensation. However, in many historicbuildings there are unheated rooms, voidstructural gaps and other spaces in which

condensation risks could increase if otherparts of the building were upgraded and/orair infiltration rates were reduced too far.

Preventing the distribut ion of moisture-laden air t hroughout the building, particularly to unheated spaces, by p assive or m echanical ventilation close to the source In somehistoric buildings or at least in parts of them it may be impossible to install suchsystems without damaging their character.In addition, and as discussed below, animportant source of moisture is frequentlythe building itself.

In developing the design of a new building ora major refurbishment, the balance betweenheating, ventilation and insulation can beadjusted until desired results are achieved, i.e.minimising risks whilst meeting Part Lsquantified Requ irements. T he text of the third

edition of Stirling (2002) identifies (with anR in a green box) issues affecting buildingswhich are being renovated, altered orconverted. However, these relate to strategieswhich aim to make the details work technically. In a historic building, theadditional physical and visual constraintsoutlined in Sections 3 and 4 of this InterimGuidance Note may make it impossible toapply some of the remedies advocated.

Even if a historic bu ildings features were

completely set aside as constraints, the strictapplication of Part L would often not beappropriate technically. For example, giventhe constru ction and environmental behaviourof some historic buildings, the least riskysolution could well require less insulation andmore heating and/or ventilation than Part Lenvisages. T his is another reason why, forhistoric buildings, D T LR d ecided that Part Lshould allow discretion to be exercised indetermining what is reasonable.

7.4 Most historic buildings need tobreatheMost historic buildings are made of porousmaterials and do not incorporate the barriersto external moisture ( cavities, rainscreens,damp-proof courses, vapour barriers andmembranes) which are taken for granted in themajority of modern construction. As a result:

condensation within the construction or in

at corners)

Box 7 The m ain risks to histor ic buildingsIn brief, these are

trapped moisture within the construction

unheated areascondensation at thermal bridges (especially

insufficient ventilation and heating to removemoisture

historic structures tend to be wetter as thereis often some rising and penetrating dampporous, breathable construction allowsmoisture to evaporate internallymore ventilation is needed to removetranspired moisturein addition, better heating may causeinternal moisture levels and dewpoints torise, because of faster evaporation frompermanently damp fabric. T his can be aparticular problem in intermittently-heateddamp buildings, which self-humidify asthey warm up.

Changes to the fabric of a building in order toreduce heat loss can alter its moisture transfermechanisms, including the ability of the fabricto breathe. Three important aspects of moisture transfer contribute to m aintainingthe balanced environment found in m anyhistoric buildings:

permeability the capacity to allow watervapour to pass throughcapillarity the ability to mop up or wick away water as liquidhygroscopicity the tendency actively todraw moisture from air and store it

A modern approach to the moisture problemsoutlined above would be to insert air gaps andmoisture barriers. Where insulation is added,particularly internally, vapour control is alsoessential in m ost modern constructions toavoid interstitial condensation. However, in a

historic building, moisture movement throughthe structure (transpiration) can be importantto the soundness of the building, e.g. cobearth-walled housing in Devon. Imperviousmaterials intended to stop indoor moisturepassing through the fabric of a modernbuilding instead stop structural moisturegetting out. Even in some modernconstructions summer condensation canoccur on the outside of a vapour control layer(see Stirling 2002, section 3.10).

T herefore proposals to add insulation tohistoric buildings need to be carefullyconsidered, for example:

Is it desirable to add insulation, or will thisincrease risks and hide problems?How much insulation should there be ( toomuch might lead to interstitial condensation)?What properties should the insulation have?(It m ay need to be m oisture resistant, andto have a controlled amount of breathabilityto allow water vapour to pass through whileat the same time avoiding interstitial

condensation.)T hese points are developed in the followingsections, particularly Section 10 ( Walls ). It isinteresting that in recent years both theecological building movement and technical

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developments have begun to rediscover thepracticalities of breathing construction,although some aspects of the theory and of the performance of traditional buildings arenot yet fully characterised.

7.5 Ventilation Requirements

Owing to the factors discussed above,historic buildings usually need moreventilation than modern ones. In the past,they were often more ventilated than strictlynecessary because of loose-fitting doors,windows and other openings. In addition,open fires created generous rates of exhaustventilation through chimneys at times whencondensation risk might otherwise havebeen high.

However, if ventilation of a historis reduced too much, condensaand fungal growth may occur,deterioration of the fabrpossibly health problems for occupants. G reatcare is therefore required in selecting anappropriate ventilation rate for a historicbuilding. A rule of thumb used by somedesigners is twice as much as required,though the actual amount needed varies withcontext, and par ticularly with the amount of evaporation occurring from the fabric.

Box 8 Controlling moisture levelsSuccessful control of moisture levels in ahistoric building often depends on:

plentiful sources of ventilation permeable building materials that arehygroscopic and hence buffer moisture

the absence of barriers to moisture flow.

leading to

11

Diffusion losses

Exchange with

Occupants

Occupants

Leaky

Exchange

ExchangeRainwater

C on

d en

s a t i on

Modern building Histor ic building

Diffusion losses

Plaster

Insulation

ic buildingtion, mould

ic and contents, and

Figure 3 Diagram showing the typical differences in movement of moisture between a historic (right) and a modern building. (Digital image by Robyn Pender)

Extract fan

fabric

Ventilation

windows

with fabric

with fabricpenetration

Capillaryrise

Vapour barrier

Ventilation

Well sealed window

Trickle ventilator(controllable ventilation)

Damp proof membrane

Capillary rise

Vapour barrier


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7.6 Thermal bridgingIf the thermal performance of one element isimproved by adding insulation while anadjacent area is not insulated, a local cold spot known as a thermal or cold bridge iscreated. For example:

it may be possible to place insulation over aceiling but not at the head of the adjacentwall at the eaves, which will remain coldalternatively, a wall may be internally linedbut not the window reveal so here theexposed edge of the newly-insulated wallactually becomes colder, and at greater risk of condensation.

If such weak spots cannot be successfullydetailed (see Stirling 2002 for modernexamples), then ad ded insulation may not bedesirable, or the amount of heating andventilation may need to be increased to helpavoid mould growth or condensation.

8 W indows

8.1 The importance of windowsWindow openings and frames establish thecharacter of a buildings elevation. Th eyshould not generally be altered in theirproportions or details, as they areconspicuous elements of the design. Thedepth to which window frames are recessedwithin a wall is a varying historical feature of importance and greatly affects the character

of a building: this too should be respected.

T he importance of conserving traditionalfenestration and its detailing cannot bestressed enough, being particularlyemphasised in PPG 15 Annex C (D NH andD oE, 1994). T he Secretary of State hasdismissed over 90 per cent of appeals againstthe refusal of Listed Building Consent forreplacing traditional single glazed sashwindows with double glazed PVCu windowsbecause the rep lacements p roposed woulddetrimentally affect the special character andappearance of the building. T he fundamentalobjections, amongst many, are that doubleglazed sealed units fatten the dimensions of glazing bars inappropriately, or result inextremely poor facsimiles stuck to the face of the glass.

Old glass is of interest and is becomingincreasingly rare. It is of value not just for itsage, but because it has more richness andsparkle than todays flat sheets with theiruniform reflections. Where it survives, it must

be retained and alternative means of thermalimprovement considered.

Four photographs at right: see fig 6 caption

Figure 4 Enlarging the window openings and setting the framesflush with the faade (left) totally distorts the proport ion anddetailing of the original windows (right). (Photograph courtesy of Kit Wedd)

Figure 5 Historic glass, especially Crown glass, is rare and cannotbe reproduced today. Where examples such as the middle rightpane survive, they must be preserved. (Photograph courtesy of Treve Rosoman)

dc

a b

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Many historic windows, frames and glazing,have fallen victim to inappropriatereplacements, but over the past decade, therehas developed a greater appreciation of theirvalue. H owever, many windows are stillthreatened and Part L must not become theagent for their thoughtless destruction. Whilelisted buildings enjoy some protection,unlisted buildings are at high risk evenwhere they are in Conservation Areas,National Parks, Areas of Outstanding N aturalBeauty and World Heritage Sites.

8.2 W indow types and mater ialsT he UK has a rich tradition of differentwindow designs and materials from variousperiods of history. Most historic windows aretimber-framed. Oak joinery (either fixed orin casements) predominated until the late17th centu ry, when, with the advent of thesash window, softwood was imported from

Scandinavia and the Baltic States. T his slow-grown, high-quality, naturally durable timber

continued to be widely used un til the early20th centu ry, when inferior species started tobe used which needed chem ical preservativesto provide some degree of longevity. Historictimber is therefore not a renewable resource:it is very difficult to source timber of thisquality and durability today. Where possiblewindows should be repaired and continue tobe used.

Iron frames had been used in medieval times,and by the 16th century metal-framed glasswindows were beginning to appear in secularhomes. By the middle of the 18th centurymetal sash windows were being cast and evencopper was being set in wooden frames,usually oak. All-metal window frames, bothsash and casements, were introduced in theRegency period in housing and industrialand institutional buildings. Mass productionin the early 20th century allowed hot-rolled

steel to be used for, among other s, thefamous C rittall windows which were strong,

slim and non-combustible. All these windowsare importan t historically and should beconserved.

8.3 Ventilating and draughtproofingMost modern windows accommodate tr ickleventilators for controllable backgroundventilation, to meet the Requirements of PartF of the Building Regulations (DET R, 2000).Older buildings often have considerable airinfiltration through floors, airbricks, etc andmay well not need more. Indeed, airinfiltration through old windows is oftenexcessive, so draughtproofing and weatherstripping can be very effective in reducingnot just heating bills by limiting the numberof air changes per hour, but also reducinglevels of noise and dust too. However, careshould be taken to provide adequateventilation to remove internally generatedmoisture and pollutants, together with

additional moisture from sources such asrising damp (see Section 6.6) .

Figure 6 Examples of the wide variety of timber [left] and metal windows [below] found on historic buildings. In (e) the upper part of the frame is metal, the lower part timber. In (f) the thin steel framesof the windows by Critt all are important t o the design of this Grade II* Modern Movement building (Connell Ward Lucas, 1932). [Photographs (a), (c) and (d): English Heritage Building Conservation andResearch Team: (f) and (i), Chris Wood: (e), (g), and (h) courtesy of Jill Channer, copyright Jill Channer]

e g

i

f

h

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14

Several forms of draughtproofing areavailable, which operate in different ways:

Some types simply act as gap fillers, andare applied as mastic or foam.

Other forms keep out the weather by meansof a snug, slightly oversized fitting,comprising silicone rubber tubes,polypropylene and nylon-filled pile brushes,or with rubber, polyester, or sprung-metalZ and V fins.

For steel and timber casements, a self-curingsilicone rubber sealant can be injected into thegap between the window and the frame.T hewindow is first cleaned, and overhauled so

that hinges and catches operate easily. T heopening edge of the casement is temporarilycoated with a non-stick gel. T he silicone isthen injected and sticks to the non-treatedframe, but not to the coated casement edge.

8.4 Improving window insulation

No historic window can reach the U-valuesrecommended in Part L ( i.e. 2.0 2.2 W/m 2

deg C: see Glossary ). So-called facsimilereplacements have been developed withdouble-glazed sealed units and low emissivityglass, but in most cases these fail to provide anadequate visual alternative owing to the framethickness required to accommodate the glazingcavity. It is impossible to replicate originalglazing bars in double glazing. Except wherereplacement is inevitable, the aim shouldusually be to improve thermal performancewhilst retaining the existing windows.

Recommended methods of improvement arediscussed in English Heritages Framing

Opinions Campaign publications (EnglishHeritage, 1994).T hese include:

Draughtproofing, as described in 8.3.T hisis the most cost-effective and least intrusivemethod.

0

8

7

6

5

4

3

2

1

1

9

26

)

1

2

3

4

5

6

7

8

9

10

has roughly the same effect as fitting an

acetic acid which can damage

alcohol

Figure 7 1 Plastic or sprung metal V or Z strip Glued or pinned silicone rubber tubing 3 Parting bead(Ventrolla) 4 Meeting rail brush (Ventrolla) 5 Bottom sash/sill brush (Ventrolla) Parting bead weatherstrip (Mighton)7 Brush for meeting rails (Draftseal) 8 Standard weatherstrip (Mighton) 9 Staff bead or butt on rod (Ventrolla) 10 Siliconeseal (Draftseal) (Digital image by Robyn Pender from English Heritage original line drawing)

Figure 8 Draughtproofing str ip being inserted into a routedchannel on the bottom rail of the top sash. (Photograph courtesy of Ventrolla Ltd)

Figure 9 Secondary glazing can provide very effective thermalimprovement. In historic buildings its successful insertion dependson fitting within the reveal in such a way as not to damagehistoric fabric. However, secondary glazing can sometimesproduce an unsatisfactory reflection when viewed from theoutside. ( Photograph courtesy of Kit Wedd

A good draughtstrip should insulate, bedurable and inconspicuous. A number of firms now provide an effective specialistinstallation and refurbishment service forexisting windows. According to one leadingcompany, these products reduce the n umber

of air changes from between 2.5 and 3.0 to0.7 per hour. In terms of reducing heat loss,draughtproofing a single-glazed window

additional sheet of glass.

Box 9 Silicone sealants: a warning noteCare should be taken in selecting silicone

sealants, as some (but not by any means all)mastics producepainted surfaces and corrode metalwork.Thesafer alternatives produce which simplyevapor ates. Always be aware and readmanufacturers labels.


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Figure 10 Shutters are not just historically impor tant, they canprovide significant thermal improvements as well as enhancedsecurity and reduction of dust and noise. (Photograph: (b) courtesy of Matthew Slocombe and the Society for the Protection of Ancient Buildings: (a), (c), (d) and (e) by Chris Wood and other members of English Heritage Building Conservation and Research Team)

a

e

Secondary glazing improves insulation,draughtproofing and noise control. If carefully designed, it can be relativelyunobtrusive, e.g. with divisions in the

glazed panels hidden behind meeting railsor glazing bars. However, not all windowsare suitable for secondary glazing, owing tothe narrowness of the internal sill orreveals; the difficulty of accommodating the

b

c

d

new panes within an oddly-shaped orunduly protruding architrave; or clasheswith internal shutters.Old louvred and panelled external shuttersare important features and often contributeto the design of an elevation. Repairing andusing close-boarded and panelled externaland internal shutters can minimise heat lossat night and when rooms are u nused, and

also reduce unwanted solar gains. Internalshutters can also be draughtproofed toimprove thermal performance, in a similarmanner to windows.

Trad itional means of minimising heat lossare still effective, such as heavy linedcurtains. Modern alternatives includeinsulated curtains an d reflective and/orinsulated internal b linds.

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+ curtains

U ~ 3.6 *

Single-glazed Double-glazed12 mm gap

Double-glazedLow

Single-glazedSecondaryglazing

Single-glazed+ night shutters

U ~ 4.8 U ~ 2.9-3.4U ~ 2.0U ~ 2.8 U ~ 3.0 *

Figure 11 Indicative U-values applied to ver tical glazing, assumingwooden or PVCu frames. (The values shown are in W/m 2 deg C:see Glossary .) Estimates for single-glazed windows (withoutdraughtproofing) with shutters or closely-fitt ing lined curtainswith pelmets apply when they are closed. Thermally insulatedcurtains would improve the effectiveness even more. It is hopedthat the results of detailed testing of these will be published in amore comprehensive document: see 2.5. (Digital image by Robyn

Pender)

8.5 RooflightsMost old rooflights are single-glazed, set incast iron or timber frames, or sometimes withunframed sheets of glass replacing slates orplain tiles. Frames are often ill-fitting, anddraughtproofing may improve this. Wherereplacement is essential, double-glazed copiesof original rooflights are available which canbe acceptable in historic buildings.

9 Doors

9.1 Typical constructionMost external doors on historic buildingswere made of timber, many in hardwoodframes. Depending on their age and designthey were usually morticed and tenonedtogether, either in a flat plane, or with panelsfitted between stiles, and muntins and rails.Doors which are original or of historicalinterest mu st be kept.

9.2 Thermal propertiesSolid doors often have reasonable insulatingproperties. Most of the heat loss usuallyoccurs by infiltration around the perimeterof the door or where gaps have developedaround panels, at the junction with the doorcloser, through locks, etc. Repairs anddraughtproofing may be helpful. Where spacein the plan form and architecture permit, aninternal draught lobby with a well-fitting (andif necessary well-insulated) inner door may bea practical solution.

9.3 Glazed doorsIf a door including the frame has morethan 50 per cent of its internal face glazed,Part L treats it as a window (see Section 8

above). Existing glazed doors should beretained, and all original or historicallyimportant glass kept. It will often be easiestto improve thermal performance with thick insulated curtains or a draught lobby, if thesecan be fitted without detriment to other

historic or architectural features.

10 W alls

10.1 External appearanceHistoric buildings display a wide range of materials and forms of construction, rangingfrom stone or earth walls perhaps two metresthick, to timber-framed buildings withcomparatively thin and lightweight wattle-and-daub infill panels. T he app earance of the

external walls is usually one of the mostimportant aspects of a historic building, whilethe materials give the building its unique andoften local character. Other than repairs orrepointing, they are unlikely to tolerate muchchange without exacerbating decay problemsand detrimentally affecting their specialinterest and appearance.

10.2 The use of porous materials inwallsMost historic buildings in the UK have solidwalls in porous materials, with internalfinishes such as lime plaster, which is itself porous. T his porosity has helped to keepmany buildings in good condition.

On the outside, it acts as a thick overcoat,absorbing rainwater, and allowing it to rundown, drain out and later to evaporate.On the inside, it helps to stabilise moisturelevels in rooms and often averts surfacecondensation, for example in crowdedconditions or when cooking.Moisture can also pass through the walland evaporate both externally and

internally as conditions allow, as can anydampness rising from the earth.

T his approach differs greatly from m ostmodern buildings, which rely on:

impervious or rainscreen systems externally

internal construction which is completelyprotected from m oisture at least in theory by cavities, damp-proof membranes, andvapour control layers.

10.3 The importance of transpirationWhere walls need to transpire moisture andvapour effectively, new mater ials whichwere intended to form barriers to unwantedmoisture or water vapour can impede thevery processes which helped a historic wall toendure. Examples are common place,including:

hard cement m ortar pointing which catchesrainwater and diverts it into a wall, bypassing the overcoat effecthard external rendering, intended to keepthe rain out, which also stops moisture

evaporating and causes the wall to becomedamper. When cracked, it also trapsrainwater, making things even worse.modern imp ervious paints which causepreviously sound plaster to break down,because rising and penetrating damp canno longer evaporateother impervious materials appliedinternally which cause moisture toaccumulate. T his in turn leads to decay of embedded m aterials (such as timber) whichare hidden from sight until deteriorationhas become severe. T he imper vious layerscan lead to a build-up of salts in theunderlying substrate. The salts thencrystallise and rupture the originalconstruction.

Many insulation products lose their insulatingqualities when wet, so moisture from dampwalls or interstitial condensation can makethem useless. Other products, including somenatural materials, are less affected. However,care must be taken in selecting appropriatematerials that do not result in new problemssuch as insect infestation.

10.4 Improving insulation externallyT he opportun ity to improve the thermalperformance of walls externally will often belimited in a historic building because of the

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impact external insulation has on theappearance of the building: notably on itsproportions, and on details such as qu oins,window reveals, cills, thresholds etc allunacceptable in terms of planning and L istedBuilding Consent (see Section 10.1).However, there may be opportunities toinsulate externally, for example where tilehanging or weatherboarding has to beremoved and replaced; or where a wallsuffering from chronic driving rain problemshas to be re-clad. Another possible exceptionis where rendering requires completereplacement. However:

Modern external insulation and renderingsystems, though technically possible, maynot be app ropriate owing to thedimensional differences.Whilst a render which is thermally moreeffective might be used, the main criterionis that repairs should be carr ied out on a

like-for-like basis, which means adhering tothe or iginal mix of mater ials. T his is alsoimportant where transpiration is required(see Section 10.3).

10.5 Improving insulation internallyIn historical terms it is important to ensurethat internal walls are always investigated withcare in advance of any changes, in caseancient or interesting features such as earlyplaster and paint schemes are hidden in theplaster or behind panelling or other coverings.

T imber panelling, plaster mou ldings orenriched decorations are all-important andneed to be p reserved.

Where complete internal re-plastering isrequired particularly where it has been donebefore and when little or nothing of historicinterest survives there may be opportunitiesto incorporate internal insulation. However:

T he dimensional changes may beunacceptable at window and door openingsand where original surface details such asdados, cornices, etc survive.T he loss of space may also be unacceptable.Moisture may be trapped and interstitialcondensation may occur.Insulation covers up the mass of internalwalls, reducing their effect in stabilising theindoor temperature and humidity levels.T hermal bridges may occur at edges and

junctions, e.g. between floors and internalwalls.

11 Floors

11.1 Flooring generallyT he appearance of a floor can be a highlydistinctive feature of a historic building.Generally floors should not be lifted because

of the damage that is inevitably caused: aworn, uneven appearance is also often valuedand cannot be completely re-created.However, if floors have to be lifted orreplaced, there are opportunities to improveinsulation.

11.2 Solid floorsSolid floors, such as those laid with stone,brick, early concrete, plaster or lime ash,cannot be insulated without first excavatingthem. Generally this should be avoided,unless it is the only way to remedy somedestructive defect. In reconstruction, damp-proof membranes will usually be incorporatedboth as normal practice and to protect theinsulation. However, membranes can causemore problems by driving moisture up wallsand columns.

11.3 Suspended floorsFloorboards can often be lifted and insulationinstalled with comparative ease (Hughes1988). However, care should be taken if:

the floorboards have a structural function,i.e. acting as a plate membrane in early18th-century construction: houses havebeen known to collapse when all thefloorboards on one level were removedat onceearly wide hardwood boards (usually oak or elm) are used, particularly if these havebeen undisturbed and cannot be liftedwithout causing damage to the boardsor joiststhere are historic examples of sounddeadening or fireproofing between joists:these should be preserved.

Some methods used with modern suspendedtimber floors are outlined in Stirling 2002,Section 5.15, and will sometimes suit historicbuildings too.

11.4 Underfloor ventilationSuspended t imber floors are or should b e ventilated un derneath. T his is usuallyintended to be cross-ventilation betweenunderfloor openings or air bricks on oppositesides of the building. However, in practice, airoften comes in through external openings andthen passes between the floorboards beforerising up within the building or into flues.Adding insulation (or floor coverings) canreduce this airflow and increase moisturelevels both under the floor and in the

building. T he adequacy of underfloor andbuilding ventilation should therefore bechecked. Some information on modernconstruction (in Stirling 2002, Section 5.17)is also relevant.

12 Roofs

12.1 External appearanceT he roof of a historic building is often itsmost striking feature. Most have survived inremarkably unchanged condition for manycenturies. With stone, slate or tile, re-coveringtends to become necessary when the fixingsfail; and much of the covering material isoften re-used on the same building orelsewhere. With thatch , shingles, lead andother metals, failure is more often attributableto the natural life of the covering itself.

12.2 Roof structureUnless there has been substantial waterleakage, the roof structure will usually be ingood condition. Often this is attributable tothe generous amount of ventilation in historicbuildings and in their roofspaces. Eventhough a historic building may generate a lot

of moisture internally some of which findsits way into the roof it is quickly removed.T he moisture-buffering effect of the largeamounts of hygroscopic material in manyhistoric buildings can also be helpful.

12.3 Improving thermal performanceProposals to improve the thermalperformance of the roofspace have to beconsidered in relation to the use andperformance of the rest of the building.For example:

modern living tends to introduce more moisture into buildings and roofspacesventilation rates are often reduced,exacerbating the problemthe air and vapour control layers (AVCLs)often used in modern constru ction arevirtually impossible to install in existingceilings with any degree of effectivenessadded insulation tends to cause roofspacetemperatures to drop, adding to potentialmoisture p roblems.

Issues and solutions tend to vary with thetype of roof: pitched or flat, with or withoutventilated roofspaces. T hese are out lined inthe following paragraphs.

12.4 Pitched roofs with ventilatedroofspacesFor t raditional roofs with cold roofspacesventilated by outside air, it will often bepossible to lay insulation over the ceilings orbetween floor joists in the conventionalmann er. T he use of semi-rigid batt s willguarantee a minimum thickness, but a widerange of other materials is also available.

Air infiltration from the building into theroofspace should be reduced, in par ticular byclosing up holes around p ipe, duct and cableroutes, especially from high humidity areas.

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Even where holes are well sealed, air andwater vapour from the building will still getin. In winter, the extra insulation makes theroofspace colder than before, so the risk of dampn ess and condensation may increase,particularly if ventilation is limited or poorlydistributed.

Sometimes additional roofspace ventilationmay have to be introduced. However, researchhas shown that not all roofs in historicbuildings particularly low-pitched ones benefit from this. Beneficial effect is lackingwhen the extra ventilation serves merely tolower the temperature while not sufficientlydiluting the moisture which escapes into theroofspace from the building below. In suchcircumstances it is essential to understandwhat is happening to the internal environmenthere, in order to determ ine the likely effect of insulation and ventilation on the existing

fabric; and not to introduce additionalventilation gratuitously.

12.5 Pitched roofs with insulation atrafter levelWhere there are rooms in the roof, Stirling(2002) recommends a 50 mm ventilation pathbeneath the roof finish, insulation, a vapourcontrol layer, boxing to contain service runswithout perforating the vapour control layer,and an internal lining. It is important tomaintain the through flow of air when

detailing new dormers or rooflights. Fewhistoric buildings would meet theserequirements.

When upgrading utilitarian attic spaces,however, it may be sometimes be possible toadop t these modern details. Alternatively,improved insulation can still be provided andthe extremes of driven rain or snow combatedby traditional means. Such app licationsmaximise the permeability of the structureeffectively absorbing most of the increasedmoisture in the short term, and allowing it todisperse slowly (Figure 12).

12.6 Flat and low-pitched roofsMost historic flat roofs are covered with lead,a few being clad in zinc or copper. Repairsand replacements using bitumastic materialsand felts have been widely used. Flat roofsshow a wide variety of designs, although mostare akin to the cold roof with a smallroofspace (sometimes deliberately ventilatedto the outside, but often not) above theceiling. Some roof-decks in fact form the

ceiling, though this is mostly confined tochurches.

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Figure 12 An attic being converted for use as a habitable room where the requirement was not t o strip the stone slates. Traditionaltorching prevents ingress of driven rain,and protection and thermal improvement is provided by: torching,a lightweight permeablebuilding paper to underside of rafters, natural wool insulation, cellulose/jute batts,wood fibre boards and a lightweight mineral woolinsulation board (or reed board) coated with lime plaster and subsequently limewashed. (Photographs courtesy of Richard Oxley,Oxley Conservation, Richard Oxley)

Boarding

InsulationVapour control layerCeiling

Lead sheet on underlay

Vent ilated cold roof

Ventilated air space

Boarding

Ceiling

Lead sheet on underlay

Typical existing roof uninsulated and often unventilated

BoardingBreather membraneInsulationVapour control layerRoof deck

Ceiling

Unventilatedair space

Lead sheet on underlayVentilated warm roof

Ventilated air space

Figure 13 Examples of flat roof covered with lead:1 Insulation of typical cold roof 2 Research has shown that despite lack of insulationand ventilation this form of roof structure has performed well. 3 Recommended modern practice which is acceptable on historicbuildings provided that historic detailing is not adversely affected by the raised roof structure. ( Digital images by Ray Mart in,adapted with kind permission from the Lead Sheet Association for reference to the Associations original drawings )

2

3

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12.7 Flat roofs with ventilated colddecksT hese have always been p roblematictechnically. According to Stirling (2002) theyare a poor option in the temperate, humidclimate of the UK and usually it is notpossible to u pgrade their thermal insulation.If there is no alternative to cold deck designs,Stirling recommend s providing a continuousvapour control layer above ceiling level,lapped and taped throughout, and also sealedto the walls at the edges. Service penetrationsshould be avoided unless this is impossible, inwhich case they should be carefully detailedand effectively sealed. Cross-ventilationshould be generous, without any blockages,and with op en eaves at each end: cold roofsshould not be used if the structure spansbetween parapet or abutment walls.

In spite of the ab ove, research has shown that

even with little roofspace ventilation and noair and vapour control layers at ceiling level,lead roofs have often survived well by virtueof the balanced environment which has beencreated. T he summ er heat dries the timbersand other porous materials in the roofspace.In winter, moisture from below is absorbedor buffered by the timber which then driesout thorou ghly again in summer. In effectthis mechanism has allowed some metal roofsand timber structures to survive forcenturies. Adding ventilation and insulation

to this type of constr uction or increasingmoisture levels within the building canchange these conditions for th e worse.Moisture problems affect not only the timbersubstrates and roof structure, but can alsoshorten the life of metal roof coverings byinducing corrosion on the underside.

12.8 Flat roofs with warm decksTo upgrade the insulation of a cold flat roof,Stirling (2002) states that the preferredoption is to convert it to a sandwich orinverted warm deck roof. However, whilesandwich construction can work for felt andasphalt roofs, installations in the 1970s and1980s showed that a continuously-supportedmetal sandwich roof could draw externalmoisture into the sandwich itself and sufferfrom decay and corrosion. Lead roofs onhistoric buildings were particularlysusceptible, as described in EnglishHeritages Advisory Note on the subject(English Heritage and LSA, 1997) and warmroofs are not recommended.

12.9 Ventilated warm roofsMod ern p ractice for metal-clad roofs is setout in the three volumes of the Lead SheetAssociations M anual (LSA, 1990, 1992,1993), which advocate the use of ventilated

warm roofs. T he p rinciple here is the creationof a new insulated and ventilated roof deck structure, completely isolated from below.If this is correctly detailed and carefullyconstructed it is an effective design, but greatcare is required with continuity of ventilationand of vapour control, as discussed in Lead roofs on historic buildings (English Heritageand LSA 1997). However, on some historicbuildings, notably those where the roofs areprominent or the abutment detailing orappearance is important, e.g. under aclerestorey window cill or low parapet,it is not acceptable to raise the roof by therequisite height often about 250 m m. T heremay also be structural p roblems. In thesecases, the oppor tunity to imp rove insulationmay be limited, and it is important to heedthe warning about the gratuitous introductionof additional ventilation.

12.10 Materials and details

Thermal bridges can occur at gaps in theinsulation and at junctions with chimneysand outside walls. Care will be needed toensure that these do not introducecondensation problems, as d iscussed inSection 7 of this Interim Guidance Note andStirling 2002, Section 2.

Sarkings T ile, stone and slate roofs used tobe laid without sarking felts, although sarking

boards were occasionally used. Re-roofingtoday almost invariably includes underfelts,to allow re-roofing to take place in badweather; and t o provide secondary pr otectionagainst wind-driven snow and rain. Vapour-permeable materials are preferred: as ageneral rule, the more vapour-perm eable thebetter. However, even they reduce airmovement, and alternative p rovision forventilation may be necessary, thoughdesigned breathing construction is nowbecoming possible. Additional ridgeventilation can be unsightly.

Insulating foam Isocyanurate is sometimessprayed directly onto the underside of slatesand tiles, and sets into a hard layer withstrong adhesive properties. Foams areclaimed to improve insulation andwaterproofing, prevent t iles or slatesslipping, and avoid condensation. Sprayedinsulating foams on slates and tiles areNOT recomm ended for historicbuildings: they prevent the slates and tilesbeing salvaged during the next re-roofing,

the tiling battens and the upper parts of therafters are sealed in, which may lead torotting and premature degradation, and thenormal flow of air into the roofspace isrestricted.

Thatch provides one of the best naturalinsulators and should not n eed furtherinsulation. A 300 mm thatched roof made of water reed (thermal conductivity 0.09 W/mdeg C) or straw (thermal conductivity 0.07W/m deg C) will have a U-value of 0.3 W/m 2

deg C and 0.23 W/m 2 deg C respectively.

13 Building services

13.1 IntroductionSometimes the building services in a historicstructure will themselves be of historicinterest. If so, advice will need to be soughtfrom the Conservation Officer on whetherthey should:

remain in use unalteredbe refurbished and re-usedbe left for visual effect or for historicreasons but be functionally replaced

be taken carefully into storage.Apart from these considerations, the energyefficiency of building services in a historicbuilding should cause few problems, providedthat care is taken. Much advice is available inCIBSE Guide F (1998), and in thepublications of the Energy Efficiency BestPractice programme.

More relevant detailed advice on strategies,equipment and installation is expected to beincluded in Energy efficient building services

and fabric for historic building: a good practiceguide for historic and traditional buildings(C IBSE, in p reparation). Only brief notes aretherefore includ ed below.

As a matter of good practice, but particularlywhere improvements to the fabric areimpossible, it is important to considerimproving the services to a level beyond theminimum service efficiency required in Part L.

Figure 14 Sprayed foam used as a way of avoiding stripping a nailsick roof and providing some insulation is NOT recommendedgood practice on a historic building. (Photograph courtesy of Kevin Stubbs, Bursledon Brickworks Conservation Centre)

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T he last twenty years have seen significantadvances in efficiency (e.g. of boilers, lampsand controls) and the replacement cost of oldinefficient equipment can often be quicklyrecovered in fuel cost savings.

13.2 Physical installationFitting and replacement of servicesinstallations must be done carefully, avoidingunnecessary damage to the historic fabric byshort-lived services elements and observingthe principles of reversibility and minimumintervention. Th is relates not on ly to holes,chases, and fixings, but also to the direct andindirect damage to historic objects by theproximity of services, for example by:

covering up or interrupting the view of important features and detailspassing too close to important surfaces(e.g. of plaster or panelling) which mightbe consequentially damaged in the course

of the work or in use afterwards (e.g. fromdirt traps and/or from cleaning behind p ipelagging run close to surface)staining by patterns of heat and airmovementdisturbance of the heat and moisturebalance leading, for example, tocrystallisation of salts in walls and damageto details and surface finishes.

Constra