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.


In an average British home about 33%* of the heat is lost through the walls. Installing wall insulation will substantially cut this heat loss, making the room more comfortable and easier to heat. It can also reduce your heating bills (and associated carbon emissions) by up to 15%*.


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.

Cavity wall insulation:

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.

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 5 years or less due to the yearly energy bill savings you will make. 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 semi-detached house are roughly £13,000 for external wall insulation and £7,400 for internal wall insulation. These costs could be reduced when carrying out the work alongside other home improvements or by tackling the house in stages. A typical semi-detached house might reach an annual saving in energy bills by up to £260.

More information is available on the Energy Saving Trust website.

Further information:

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

Certain households might be entitled to support under the Energy Company Obligation (ECO). Under this scheme medium and larger energy suppliers may fund the installation of certain energy efficiency measures. Find out more information about the scheme and if your eligible via Ofgem.

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