Cavity wall insulation is insulation material inserted into the cavity between the two leaves of a cavity wall.
In modern homes rigid foam boards or semi-rigid mineral-wool or glass fibre “batts” are inserted during construction.
In older homes where the cavity was originally left unfilled insulation can be injected or blown into the cavity. Materials used for this purpose are loose mineral- or glass-fibres, urea formaldehyde foam and bonded polystyrene beads. The insulation material is injected through small holes drilled into the mortar between courses of the outer brickwork – these holes are then filled in, leaving little external evidence of the insulation.
When Cavity wall insulation has been inserted into an existing home the installer should be registered with the Cavity Insulation Guarantee Agency (CIGA) and issue a 25-year guarantee. This should be handed over to the buyer when a home is sold.
Concerns have been raised that Cavity wall insulation can cause a variety of problems if it is not properly installed. These include:
- Dampness caused by moisture penetrating the exterior wall and being transmitted across the cavity to the interior walls of a property. The purpose of the cavity in a cavity wall is to stop moisture penetration. Properly installed insulation should not transmit water across the cavity, but this may occur if installation has not been carried out in accordance with manufacturers’ specifications.
- Mould and damp occurring within the cavity. This may occur if voids are left in the insulation material – water vapour in the void can then condense causing dampness and encouraging the growth of mould
- Wall-tie corrosion and failure – wall ties are an essential feature of a cavity wall, to tie the two leaves of the wall together. These ties should be resistant to corrosion, but if insulation material gets wet so that the ties are in constant contact with water they may corrode and fail. This problem has also been linked to the use of urea formaldehyde foam insulation.
- Polystyrene beads are not properly bonded – if alterations are then carried out involving cutting into a wall (e.g. when inserting a new window) the beads flow out from the cavity.
An ordinary survey should highlight any obvious problems with damp, but a proper survey may be required to ascertain the cause of problems with cavity wall insulation. This would involve drilling holes in the exterior walls and inserting a probe with a cctv camera.
If a seller does not know whether a property has Cavity wall insulation and there is no external physical evidence then a cctv probe would also be necessary.