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 dwelling 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: If your home has cavity walls, the bricks will usually have an even pattern with all the bricks laid lengthways. If your home has 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 might already be insulated  or suitable for insulation on the Energy Savings Trust website.

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 materials is usually either mineral wool or polystyrene beads, but polyurethane foam may sometimes be used instead.

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.

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 walls. Solid walls can be insulated though ‚Äď 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 on a typical semi-detached of solid wall insulation can vary with around £13,000 (External wall insulation) and around £7,400 (Internal wall insulation). Costs could be reduced by carrying out the work at the same time as other home improvements or by not tackling the whole house at once. A typical semi-detached house might reach an annual saving in energy bill by up to £260.

There is more information available on external and internal insulation for solid walls on the Energy Saving Trust website.

Further information:

Simple Energy Advice are also providing information about insulating your party walls:

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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