How does it work?

Having your cavity walls insulated couldn’t be easier. The material is normally applied from the outside of the wall through small holes which are drilled between the bricks. As the material is injected through the wall it fills the cavity completely. Once finished the holes are filled in to make as perfect a match as possible to the brickwork.

What to watch out for

Most modern houses built post war (1945) are constructed with cavity walls, however it is only those houses built post 1990 which were designed and built with cavity wall insulation built in.

It is therefore very important when considering having cavity wall insulation fitted to ensure the walls are damp free, and that there is a reliable source of ventilation to allow air movement within the walls. This also means checking the damp proof course (d.p.c.) is intact all around the house to prevent rising damp attacking the newly installed insulation, and the bricks have all been re-pointed if necessary to remove any gaps between the mortar.

Also ensure all essential ventilation openings, such as those providing combustion air or underfloor ventilation, and all flues and air bricks in the cavity wall are checked. If adequate sleeving or other cavity closures are not present, installation should not proceed until these openings have been sleeved or otherwise modified to prevent blockage by the insulant.

• If the walls are not able to ventilate air properly, the act of insulating the walls can lead to increased levels of moisture within the building which may, over time, result in potential problems with damp.

Which material?

The materials readily available for cavity wall insulation are Mineral Wool, Urea Formaldehyde (u.f.) Foam, and Expanded Polystyrene Bead. These materials all have the following properties;

These materials all have equivalent thermal insulation properties and are produced under strict quality control to ensure compliance with the building regulations and industry standards.

• Mineral Wool
• Urea Formaldehyde Foam
• Expanded Polystyrene Bead

Other materials are also available which have a much lower embodied energy rating, that is they require much less energy to manufacture and therefore have a much greater positive impact on the environment. Currently though usuage is limited to a small number of installers who work with them.

• Organic insulation materials
• Natural insulation materials

How much will it cost?

Cavity wall insulation is one of the most cost-effective energy efficiency measures in the home. An average grant aided cavity wall installation will cost around £135, which with the savings you can make on your heating bills (usually between £100 and £120 each year on a typical home’s fuel bill), will pay for itself in just over a year.

There are a range of grants and offers available to help you implement energy saving measures in your home.

Can you DIY?

Due to the hazardous nature of the products involved in cavity wall insulation, and the technical nature of the installation, it's not a good idea to do this procedure yourself.

• A specialist contractor should install your cavity wall insulation for you, as they will provide all the experience and equipment.
• They should be registered with the National Insulation Association, which covers you, via the cavity Insulation Guarantee Agency, if any damage occurs during the installation.

Further information and useful links

• Introduction to wall insulation
• Solid wall insulation
• Full guide to the building regulations
• Making structural changes to your property
• Successfully damp proofing your home
• More walls and ceilings topics
• Building works topics

• Find a Insulation Installer near you
• Find a Builder near you

• National Insulation Association
• Energy Savings Trust (est.org.uk)
• Cavity Insulation Guarantee Agency (ciga.co.uk)
• Building Regulations an explanatory booklet (odpm.gov.uk)
• Party Wall Guidance (rics.org)
• Impact of the Party Wall Act 1996 (communities.gov.uk)