Retrofitting Historic Buildings - Westminster City Council

Solid wall insulation can be a way of improving the thermalefficiency of a building, and could save energy and reduceheating bills. Most of the historic buildings in Westminster havesolid masonry walls, either of brick or stone. Masonry walls arenot good insulators and they often feel cold to the touchbecause they conduct heat. The only way to insulate them is byadding a layer of insulation either internally or externally. Around35% of heat loss from a typical home is through its walls.Advantages: This can improve the thermal comfort of a propertyand reduce energy bills substantially. It raises no planningissues for unlisted buildings in conservation areas and may incertain circumstances be acceptable for listed buildings forexample where internal finishes have already been lost. It is alsolikely to be cheaper than external wall insulation although thereare likely to be additional costs associated with the need toreapply decorative finishes, and possibly refit kitchens andbathrooms, so for this reason is best considered for wholehouse refurbishment projects.fabric this may be acceptable, but will require listed buildingconsent.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 we keepthem today. Modern materials including insulation and evenemulsion paints are more moisture resistant and can restrict theability of walls to breathe. The risk of water vapour passing into awall, but not being able to escape, is that it can condense insidethe fabric of the wall. This is known as ‘interstitial condensation’,and it may cause damage to a wall structure and finish. Thermalbridging, where water vapour condenses on relatively cooleruninsulated surfaces can also be a problem around roofs, floorjoists, windows and partition walls. Any damp problems,whether through water penetration, rising damp, or any othersources must be dealt with first before deciding on the mostappropriate strategy for internal insulation. Once this has beendealt with there are generally two strategies.Disadvantages: It is disruptive and will typically require aproperty to be empty, and probably kitchens and bathrooms tobe completely refitted. It will take up internal floorspace and alterthe relationship of the door and window reveals, and will requireskirting boards, cornicing and decorative plasterwork to berelocated. Again there are inherent risks in creating thermalbridges for moisture which can result in damp and rot problemsin localised areas, so an air gap is recommended. It is alsomore expensive than external insulation, and the additionalcosts associated with having to vacate a property andcompletely refit kitchens and bathrooms adds significantly to theoverall cost, unless such works are programmed when a wholehouse refurbishment is planned. In some situations, such aslisted buildings where there is little remaining internal historic22