Walls can be responsible for up to 40% of heat loss from a house. Cavity wall insulation can reduce this loss by up to two thirds. This depends on many factors, including the type of house – a detached house has more to gain than a terraced as it has a greater proportion of external walls.

Brick houses built after 1920 usually have a gap between the two layers of bricks in the external walls, which can be filled with insulating material. This is easy and cheap to do. Look up local installers in Yellow Pages, or contact your Energy Advice Centre. They will drill small holes in your outside walls and inject the insulating material, usually polystyrene beads or mineral wool. This simple process can pay you back within 2 years.

To check if you have cavity walls take a look at your brickwork pattern. Cavity walls have all bricks laid end to end, but solid walls include half-brick profile, which are laid end on to tie the wall. If your walls are 230mm thick or less, they are probably NOT cavity walls.

If your house was constructed after 1995, it probably already has cavity wall insulation.

If you can see a series of small filled holes at various points on your external walls, then you may already have insulation - don't confuse this with damp-proofing, which is evident through small filled holes along the lowest level of brickwork.

You may be eligible for a grant for this work.