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Cavity wall construction

Cavity wall construction has almost entirely replaced solid wall construction in the UK. It evolved in the latter years of the 19th century and was used widespread from the early 1900’s. Cavity walls work on the principle that masonry (brick and block) is a an absorbent material and will slowly draw rainwater into the wall from the outside or inside of the house. The cavity serves as a way to drain water back out through weep holes. The weep holes allow wind to create an air stream through the cavity and the stream removes water from the cavity to the outside.

A traditional masonry wall should be built using an inner and outer leaf and a cavity should be provided between them. The cavity should meet the following provisions;

  1. The cavity should have a minimum width of 50mm.
  2. The cavity should be kept clear from mortar snots to stop cavity bridging.
  3. The two leaves should be tied. Wall ties should be a maximum of 900mm horizontally and 450mm vertically.
  4. Cavity wall should always be insulated, whether partially or fully. If partially insulated a minimum clear cavity of 50mm should be provided.

How can I tell if my wall is a cavity wall?

1) As  previously stated, older houses were usually built with solid construction. So the rule of thumb is below;

If your house was built;

Before 1932 – Cavity walls unlikely

1932-1982 – Highly likely

After 1982 – Almost certain

2) You can also check the brick patterns on the outside of the wall. The common types of brick wall are – Stretcher bond, Flemish bond, and English bond.

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.

3) You can also measure the thickness of your external wall to determine if your wall has a cavity. Measure from the outside face of the wall through the door window opening to the inside face of the wall. Anything less than 30cm isn’t a cavity wall. Approximately.

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