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How to spot cavity walls

There are three simple checks which should tell you if your house has cavity walls. If in doubt a professional survey will tell you for certain.

Check 1: How old is your house?

Cavity walls didn’t start to be used in general building construction until the early 1930s. Even an old house without cavity walls may have had 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?Does it have cavity walls?
Before 1924Unlikely
Between 1924 - 1982Highly likely
After 1982Almost certain

How to spot a cavity wall.

Check 2: Check the brick pattern on your outside walls

There are three 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 also 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.

​A thickness of less than 30cm (11.5 inches) is likely to NOT be a cavity wall.
More than 30cm (11.5 inches) probably IS a cavity wall.

The above is only a rough guide. For advice contact your local Energy Advice Centre, which is run by the Energy Saving Trust (EST).