Install wall insulation

Insulating walls helps to retain heat in your house, reduce your heating needs and make you feel more comfortable. There are various ways to insulate walls effectively.


About a third of the heat lost from uninsulated homes escapes through the walls. Installing wall insulation will substantially cut this heat loss, making the room more comfortable and easier to heat.


Find out what type of walls you have

The first thing you need to find out is what sort of walls you have. If you can see the brickwork on the outside of the house, look at the pattern of the bricks:

  • With cavity walls, the bricks will usually have an even pattern with all the bricks laid lengthways.
  • With solid walls, the bricks will have an alternating pattern, with some bricks laid across the wall so you can see the smaller ends from the outside.

If the brickwork has been covered, you can also tell by measuring the width of the wall. Examine a window or door on one of your external walls:

  • If a brick wall is more than 260mm thick then it probably has a cavity.
  • A narrower wall is probably solid. Stone walls may be thicker still but are usually solid.

Some houses have a different type of wall structure altogether. If your house is a steel-frame or timber-framed building, or is made from pre-fabricated concrete, then you will need to ask a specialist insulation installer to advise you.

If your house was built after the 1920s, it is likely to have cavity walls. A cavity wall is made up of two walls with a gap in between, known as the cavity; the outer leaf is usually made of brick, and the inner layer of brick or concrete block.

If your house was built in the last 20 years or so, the walls are probably already insulated. There is more guidance available on how to find out whether your cavity walls are suitable for insulation or are already insulated on the Energy Savings Trust website.

Cavity wall insulation

Filling cavity walls is not a job you can do yourself, you will need to employ a registered installer, who can usually do this in little time and with minimal intrusion. Many cavity walls can be insulated by injecting insulation material into the cavity from the outside. A specialist company will drill holes in the outside walls, inject insulation through the holes and then seal. The insulation material is usually mineral wool or polystyrene beads, but polyurethane foam may sometimes be used instead.

Typical installation costs of cavity wall insulation vary depending on the size of your home. But whether you live in a large detached house or small flat, you should be able to make back the installation cost in 3 years or less due to the yearly energy bill savings you will make at 22/23 energy costs. You can find more estimates of costs and savings on the Energy Savings Trust website.

Solid wall insulation

If your home was built before the 1920s, its external walls are probably solid. Solid walls can be insulated though – either from the inside or the outside. This will cost more than insulating a standard cavity wall, but the savings on your heating bills will be bigger too.

Typical installation costs for a typical three bedroom semi-detached house are roughly £12,000 for external wall insulation and £8,500 for internal wall insulation. These costs could be reduced when carrying out the work alongside other home improvements. A typical semi-detached house might reach an annual saving in energy bills by up to £540.


Action on Energy Grants: provide grants for low-income households in Cambridge to install energy efficiency and low carbon heating options. The means-tested grant covers 100% of the cost of improvements for households and two thirds of the cost of improvements to homes rented out by private landlords, with landlords expected to pay the outstanding amount.

Simple Energy Advice have information on insulating party walls (walls shared by you and a neighbour).

Open Eco Homes Directory: Our Open Eco Homes directory includes links to insulation products and suppliers used by our case study eco-homes.

Airtightness: whilst installing insulation, you may want to also consider air-tight membranes which will help you to reduce your energy demand further. See our Open Eco Homes Airtightness talk and look for suppliers such a Intelligent Membranes.