Retrofitting Historic Buildings - Westminster City Council

More documents

Recommendations

Info

$Converted from C:\PCSPDF\PCS44459.TXT - Westminster City ...$

Solid wall insulation can be a way of improving the thermalefficiency of a building, and could save energy and heating bills.Most of the historic buildings in Westminster have solid masonrywalls, either of brick or stone. Masonry walls are not goodinsulators and they often feel cold to the touch because theyconduct heat. The only way to insulate them is by adding a layerof insulation either internally or externally. Most external systemsconsist of a layer of insulating material fixed to the wall andcovered by a render, which provides a degree of protection fromweather and impact damage.The major issue to consider is that external wall insulation willhave an impact visually on the relationship between the buildingenvelope and its openings, altering the detailing aroundwindows and doors, and also eaves and roof verges. It ispossible to extend roof eaves to deal with this.For this reason it would need to be very carefully designed, andin conservation areas planning permission is likely to be neededin most cases and it is likely to be contentious but it may beallowed in certain circumstances such as on the rear elevation,and only in an enclosed situation, not for part-only of a unifiedterrace, although applications to apply to the whole of a terracewould be considered. In all cases, where acceptable, thecladding would be expected to match the original facingmaterial. In addition careful detailing is required around windowsto minimise the impact of altered window reveals. Outside aconservation area, external wall insulation is likely to bepermitted development as long as it uses materials of a similarappearance to the existing buildingAdvantages: This can improve the thermal comfort of a propertyand reduce energy bills substantially, as typically 35% of heat islost through a building’s walls. This does not require theproperty to be vacated, is simpler and easier to achieve thaninternal wall insulation (although note that it may require worksuch as extending the eaves of a house in order to make itpossible). External wall insulation works better with the thermalmass of existing walls, meaning that walls which absorb heat willbe able to release it back into the interior of the building when itbegins to cool. It is also generally considered a safer solution interms of the risk of damp and moisture in a building than internalsolid wall insulation. It will not reduce floorspace internally.Disadvantages: This will probably require work to ensure thedetailing around the roof and window reveals is dealt withappropriately, which may include extending the eaves of ahouse where there is insufficient overhang. There are inherentrisks in creating thermal bridges for moisture which can result indamp and rot problems in localised areas, so professionaladvice is necessary. It is only likely to be acceptable in limitedcircumstances (see table above), and is not consideredacceptable for listed buildings.Risks: Older properties were designed to breathe, i.e. allow acertain amount of moisture in and out. Typically, they would onlyhave heating in some rooms, and would be cooler than wetypically keep them today. Modern materials including insulationand even emulsion paints are more moisture resistant and canrestrict the ability of walls to breathe. The risk of water vapourpassing into a wall, but not being able to escape, is that it cancondense inside the fabric of the wall. This is known as‘interstitial condensation’, and it may cause damage to a wallstructure and finish.Thermal bridging, where water vapour condenses on relativelycooler uninsulated surfaces can also be a problem aroundroofs, floor joists, windows and partition walls, although withexternal insulation this is less likely to be an issue.26
Walls with structural problems which cannot be repaired shouldnot be externally insulated. Any damp problems, whetherthrough water penetration, rising damp, or any other sourcesmust be dealt with first before considering whether external wallinsulation is appropriate.Breathability: It is vital to ensure that materials used in externalinsulation and weatherproofing are breathable (preventing waterpenetration from outside while allowing moisture inside or risingfrom the ground to pass out), and have similar properties toexisting walls. English Heritage recommends that progressivelayers of an insulated wall should become more permeable frominterior to exterior enabling moisture to escape. Materials toavoid include acrylic or cement based renders or pointing, nonbreathableinsulation materials and vapour barriers. In additioncare must be taken not to introduce any impermeable finishessuch as vinyl wallpaper or emulsion paint (internally orexternally), which can compromise the ability of the wall toabsorb and release moisture.Thermal Bridges: This will also need very careful detailing toensure that there are no thermal bridges, in places whereinsulation coverage is incomplete or reduced which might resultin water condensation at these relatively colder surfaces.However, if it requires work to extend roof eaves, or alterdetailing around window and door reveals, or deal with servicesthese will add substantially to the cost. It should be noted thatavailable data on typical costs for solid wall insulation tends tobe based on a typical 3 bedroom semi detached property, andin Westminster this is not typical therefore costs for Westminsterproperties including the finish and scaffolding are likely to besignificantly higher.ExternalSolid WallInsulationUnitCost(lower)Cost(Upper)Cost(average)Subsidies(refer toESTwebsite forlatest info 24Listed 80m 2 £7600 £13200 £10400 0-50%building 25Unlistedbuilding 26 80m 2 £10500 £14500 £12500 0-50%When to do this: External wall insulation is not very disruptive tooccupants, but owing to the high cost (as well as cost ofscaffolding) it is something to consider when you are thinking ofupgrading or replacing existing render.Particular care is needed around windows and doors. Specialistadvice should be sought on what is most suitable.Costs: The costs of solid wall insulation will vary significantly andare also related to property type, wall area, finish, number ofinstallations (economies of scale may apply for example tosocial housing projects where a bulk number of units can beinsulated). Although external solid wall insulation has a highercapital cost, and will require scaffolding, it may have lessassociated costs as it can be applied with residents in situ.27
Page 1 and 2: Retrofitting Historic Buildingsfor
Page 3 and 4: ContentsIntroduction 4Limitations o
Page 5 and 6: This guidance will be of most use t
Page 8: Article 4 DirectionsFor some buildi
Page 12 and 13: competent person’ scheme exists.
Page 14 and 15: MeasuresThis section outlines measu
Page 16 and 17: Installing insulation in existing r
Page 18 and 19: Floor insulation (suspended timber
Page 20 and 21: For further information see:• Fac
Page 22 and 23: Solid wall insulation can be a way
Page 24 and 25: For further information see:• Fac
Page 30 and 31: Advantages: This can improve the th
Page 32 and 33: Disadvantages: It can be more expen
Page 34 and 35: A significant amount of heat is los
Page 36 and 37: Boiler upgradeDoesBuildingRegsapply
Page 38 and 39: Heating controlsDoesBuildingRegs ap
Page 40 and 41: Micro Combined Heat and Power (CHP)
Page 42 and 43: Ground source heat pumpsDoesBuildin
Page 44 and 45: Air source heat pumpsDoesBuildingRe
Page 46 and 47: For further information see:• ‘
Page 48 and 49: Solar PV panels convertenergy from
Page 50 and 51: Solar thermal panelsDoes BuildingRe
Page 52 and 53: Living roofDoesBuildingRegsapply?Is
Page 54 and 55: Case Study: 15 Passmore Street, SW1
Page 56 and 57: Case Study: The Flagship HomeArchit
Page 58 and 59: SummaryMeasureUnlisted, within acon
Page 60 and 61: Westminster’s Planning PolicyThis
Page 62 and 63: Notes and References1 Westminster H
Page 64 and 65: 35 Town and Country Planning (Gener

Retrofitting Historic Buildings - Westminster City Council

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?