Most houses built after the 1920s will have a wall construction consisting of two leaves of masonry (brick or blockwork) with a cavity between. In older houses this cavity is empty and can be filled with insulation to reduce the heat loss through the house. A thorough inspection is required to ensure that this is a suitable measure for each individual house. Typically, the installation of cavity wall insulation is a quick job performed outside, with very little disruption caused to resident.
Unfilled cavity walls of a suitable width (50mm or more) can be insulated by drilling small holes into the walls from the outside of the home and injecting insulation such as polystyrene beads into the space.
Prior to installation, care must be taken to ensure that every cavity wall is inspected in several places to ensure they are dry and empty between cavity tray and cap, to allow the insulation to perform efficiently and stop any moisture passing through to the inner skin. Homes close to the coast or at a high elevation may not be suitable for cavity wall insulation, without further protection with external wall insulation and a careful render choice.
Following insulation, weep holes must be placed at 450mm centres at the cavity tray, free from blockage and extend through any External Wall Insulation (EWI).
Some installers may use mineral fibre or expanding foam to insulate cavity walls, however polystyrene beads are recommended as the better performing product. Fibre and foam cavity wall insulation products may also risk moisture absorption, which is virtually impossible to rectify without an extraction.