Cavity Wall Insulation

What is

Cavity Wall Insulation

Cavity wall insulation (CWI) is the installation of a blown insulation between two masonry constructed skins. First seen in the late 1960s, (when Urea Formaldehyde foam was used), the application developed through the 1970s with the use of Expanded Polystyrene beads, Mineral Wool fibre and Polyurethane foam.

Cavity wall construction was generally adopted by the building trade from around 1930, replacing solid wall construction; however, cavity walls have been identified as being built as early as 1840. Early cavity walls were mainly 100mm brick / block inner skin, a 50mm cavity and a 100mm brick or block render outer skin.

CWI is a quick and simple solution to increase the thermal efficiency of a property without any internal disruption or using the more expensive option of external wall insulation.

Cavity Wall Insulation Diagram

Are all masonry cavity walls suitable for CWI?

No not all cavity walls are suitable for CWI. It is always recommended that a pre-installation assessment is carried out first to ensure that the property is suitable, that the cavity is clear from debris and that there are no signs of damp penetration into the cavity.

Which types of properties are not suitable for CWI?

Timber and Steel framed buildings along with concrete framed and system-built properties are not suitable for CWI.

How long does cavity wall insulation last?

Following the installation of a cavity wall insulation system, you should receive a 25-year guarantee.

Will the CWI ever require replacing?

Generally the answer to this would be no, unless there has been a problem with damp penetration. If damp penetrates into the cavity, then the CWI can act as a bridge for the moisture, transferring it across the cavity. If this occurs, then there may be a requirement to extract the CWI and repair the wall.

How is CWI installed?

The installation of CWI is carried out by approved companies. 22-25mm diameter holes are drilled through the outer skin at specific positions and intervals, before the insulation material is pumped through the wall into the cavity, where it settles into position. Following the installation of the CWI, the holes are made good using coloured mortar to blend in with the external finish.

How long does it take to install CWI?

Typically a semi-detached property should take around 2 hours to be completed.

What maintenance is required after the installation of CWI?

There is no maintenance for the CWI; however, it is important that the fabric of the building is maintained in good condition as this might lead to moisture ingress.

How do you prevent CWI entering my neighbour’s cavity wall?

If you have an adjoining cavity wall which is not being insulated, the technicians will install a cavity barrier at the party wall line, which will prevent the CWI from spilling into the cavity.