Cavity Wall Insulation

Do I have Cavity Walls?

There are three simple checks you can do yourself which should tell you if your house has cavity walls. If in doubt, ask for a professional survey.

Check 1: What’s the age of your house?

Cavity walls didn’t really start to be used in general building construction until the early 1930s, so the age of your house is a useful first step. Even if you have an old house without cavity walls it may be that there has been a more recent extension which could have cavity walls, so it’s advisable to go to Step 2 and check the brick pattern on more than one wall.

When was your house built? Cavity walls?
Before 1932 Unlikely
1932 – 1982 Highly likely
After 1982 Almost certain

Check 2: Check the pattern of bricks on your outside walls

There are 3 common types of brick wall – Stretcher bond, Flemish bond and English bond. Only Stretcher bond walls, are likely to have cavity walls.

Stretcher bond, where all the bricks are laid on the long side, often indicates a cavity wall.

Flemish bond, where the bricks alternate between a full length brick and a half length brick, are unlikely to have cavities.

English bond, where there are alternating rows of full and half length bricks, are unlikely to have cavities.

Check 3: Measure the thickness of your outside walls

Cavity walls tend to be thicker than solid walls because they have an air gap between the external and internal wall. To measure the thickness of your outside walls, simply open your front or back door (or a window in the front or back walls) and measure from the outside face of the wall, through the door/window opening to the inside face of the wall.

Layers of internal plaster or external render will affect the thickness so a rough figure is all you require.

Outside wall thickness Cavity walls?
Less than 30cm (11.5 inches) No
More than 30cm (11.5 inches) Yes

Remember that the above is only a rough guide. If you are in any doubt, please contact your local Energy Advice Centre, which is run by the Energy Saving Trust.