Insulating Walls

How you insulate the walls of your home will be determined by several factors. Firstly, the type of construction. If the house was built since 1920 and certainly after 1950, it will probably have cavity walls, two skins of brick, or one of brick and one of concrete block, with a gap between through which air circulates to reduce the likelihood of water penetration. Although heat loss is slightly slower through a cavity wall than one of solid brick, it is not sufficiently insulating to substantially reduce the cost of home heating. However, filling the cavity with insulation prevents circulation, trapping the air in millions of tiny air pockets within the material, it's a process that can cut heat loss through the wall by about 65 per cent.

Solid walls require different treatment, you can either insulate the external face of the walls or line the inner surface and either of these methods can involve considerable disruption to the joinery, electrical and plumbing supplies.

Advantages and disadvantages
With cavity filling, every exterior wall must be treated simultaneously, so it is most cost-effective for homes which are heated throughout for long periods and with a properly controlled system.
Heating without controls will simply increase the temperature inside instead of saving on fuel bills. This type of insulation is impractical for flats or apartments unless the whole building is insulated at the same time.
Solid masonry walls must be insulated in some other way. It is possible to hire a contractor to clad the exterior of the house with insulation but it is expensive and alters the appearance of some buildings. The comments concerning the manner of heating and effective controls to make cavity filling worthwhile apply equally to exterior wall insulation.
Another method is to line the inner surface of either type of wall construction with insulation. It may involve a great deal of effort depending on the amount of alteration required to joinery, electrical fittings, and so on, but it provides the opportunity for selective insuiation, concentrating on those rooms which would benefit most, and it is the only form of wall insulation which can be carried out by the householder.