What is a cavity wall?

A cavity wall is an external wall of a building that consists of two layers separated by an air gap or a cavity.  Masonry (brick or block) cavity wall construction was the most common form of construction for houses built in the UK between 1930 and 1980. However, many other types of construction were also used during this period including 220mm solid brick, timber or steel frame houses as well as concrete system build.

If you can see the brickwork on the outside of the house, look at the pattern of the bricks. If your home has cavity walls, the bricks will usually have a regular pattern like this (or a stretcher bond):

cavity wall pic 1

If your home has solid walls, the bricks will have an alternating pattern like this (this is also called a Flemish bond):

cavity pic 2 solid

How do I know if I have a cavity wall?

If the brickwork has been covered, you can also roughly work out the construction type by simply getting your tape measure out and measuring the width of the wall. If a brick wall is more than 270mm thick then it probably has a cavity; a narrower wall is probably solid. Stone walls may be thicker still but are usually solid.

Sometimes you can see the cavity by looking through the frame of an opening like a window or a door; or you can go up into the loft and look at the way the eaves join to the walls.

If your house is a steel-frame or timber-framed building, or is made from pre-fabricated concrete, different rules apply. A visual check of the loft space is the best and starting point. Retro-fit cavity wall insulation would not be suitable for these construction types.

timber frame pic20150107_112330

Is the home suitable for cavity wall insulation?

Your home will usually be suitable for cavity wall insulation if it meets these criteria:

  • Cavity is clear of any rubble
  • DPC (damp proof course) 200mm-300mm above ground level
  • Your cavity is at least 50mm wide
  • The masonry or brickwork of your property is in good condition
  • The walls are not exposed to driving rain

Remedial works may be required before insulation works can take place. Extract4Homes offers cavity wall clearance for preparation of installation works.


If your property is 10 -15 years old (most houses will have insulation already) please call Extraction4Homes on 0208 8199152 to see if we can help.