CAVITY WALL INSULATION

Many house built in the 1950's and 1960's (and some built before the second world war) have external walls built with two skins of brick with a space or cavity between. Almost certainly when built, these cavities were empty, but some have subsequently been filled with insulation to improve their thermal performance. Many have not been filled.
TIP: if the walls are built of bricks, look at the bricks. If all the bricks are laid the same way with the long face showing (about 225mm-9 inches-long and 75mm-3 inches-high) then the wall is almost certainly a cavity wall. If there is a mixture of long and short bricks showing, it is almost certainly a ‘solid' wall with no cavity (see insulation for solid walls below).

Cavity walls are usually insulated using blown fibre fill. This is a specialist job for experts, but there are many contractors undertaking this work. It may be necessary to remove a brick to se if a wall has been insulated, but sometimes the fill holes can be seen