What is cavity wall insulation

What is cavity wall insulation?

We have done a lot on types of walls. If you have a cavity wall, the gap between the bricks or blocks can be filled with insulation. This is a very politicised issue. There are some instances where poor and inappropriate insulation has caused serious issues in buildings. This tends to manifest as circular spots or significant mould or other damp related issues. You can tell if your wall is cavity by following this video guide.

How can I tell if my wall has been insulated?

As part of the Legal Process the question should have been raised. You may have paperwork to this effect. If not then you need to carefully look at the external walls. You are looking for the tell-tale drill holes fairly regularly spaced in the walls. These are most notable under windows. These are around 25mm in diameter. This forms the first part of this video.

What has it been insulated with?

Urea Formaldehyde

In the drive for thermal performance in the 1970’s Urea Formaldehyde was used. Large companies such as ICI developed these foams. To be sprayed into the walls. They did not however homogenously fill the cavity and tended to spread all over the place. They left large areas untreated. At the time there were some serious health implication issues that were discovered when it starts to break down. These forced questions in the houses of parliament. The US and Canada banned these very quickly as a result. This is because the design of the US and Canadian houses was different. Often timber frames with plasterboard dry lining or Sheet rock as it is called over the pond. We had brick and block walls so the potential for gas diffusion was reduced. UNLESS you had say a Cornish type 1 house which was timber framed with plasterboard drylining.

Open cell insulation

This was blown mineral fibre; this is the white short strings that can be seen in the loft void. These once wet for whatever reason can cause penetrating dampness or flooding as they hold on to the residual moisture. When the insulation is wet it is similar to having a sponge installed between the walls. This will reduce the thermal performance massively. It can also slump over time leaving cold spots. On installation it will also not necessarily completely fill the walls homogenously. There is the added issue of rodents. If they can enter a property this gives them access through the cavity all-round the house. This is a very common issue and one often sited for their removal.

EPS (Expanded polystyrene)

This is the most recent type of incarnation of cavity wall insulation. You can often see the odd small white or grey polystyrene ball floating around the vicinity of the property or in drain gullies. It is often visible in floor voids.  This is designed to be closed cell so does not hold water if it gets wet. It should also prevent water from crossing the cavity. It also performs well thermally but does tend to escape so cold spots are a problem.


There are 25 year guarantees offered by the Cavity Insulation Guarantee Agency or CIGS. However if the insulation has been dislodged say by an extension for example these guarantees are often void.