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Cavity wall

About a third of all the heat lost in an uninsulated home escapes through the walls.

Heat will always flow from a warm area to a cold one. In winter, the colder it is outside, the faster heat from your home will escape into the surrounding air.

In general, houses built from the 1990s onwards have wall insulation to keep the heat in, but if your house is older than that it may not have any wall insulation.

If this is the case then you may be losing a lot of heat from your home, as heat can escape more quickly through uninsulated walls.

Most types of wall can be insulated in one way or another.

If you have a typical house with cavity walls, you could save up to £145* per year in heating bills just from insulating the walls. The first thing you need to find out is what sort of walls you have.

*This estimate is based on insulating a gas-heated, semi-detached house.

Jump to: Cavity and solid walls, Non-standard wall types, Commonly asked questionsMore information

Cavity and solid walls

Houses in the UK mostly have either solid walls or cavity walls:

  • 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.
  • solid wall has no cavity; each wall is a single solid wall, usually made of brick or stone.

Working out your wall type

If your house was built after the 1920s, it is likely to have cavity walls. Older houses are more likely to have solid walls.

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 a regular pattern:

If your home has solid walls, the bricks will have an alternating pattern:

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.

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Non-standard wall types

If your house is a steel-frame or timber-framed building, or is made from pre-fabricated concrete different rules apply for insulation.

Generally these houses don't have a cavity to fill, but it may be possible to insulate them in the same way as a solid wall.

However, you may need a specialist company to insulate a non-standard wall.

For further advice or to find an installer who can help you, contact the National Insulation Association.

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Commonly asked questions

What's cavity wall insulation and is it suitable for my home?

Cavity wall insulation fills gaps often found between external walls in homes built after 1920, keeping the warmth in to save energy. It can also help reduce condensation inside the house if this is a problem stemming from your external walls. It is blown into the cavity from the outside of a house. Every part of the wall must be filled with insulation, so it's important that the installer can reach all your external walls.

Your home will usually be suitable for cavity wall insulation if it meets these criteria:

  • Its external walls are unfilled cavity walls.
  • Your cavity is at least 50mm wide.
  • The masonry or brickwork of your property is in good condition.
  • It is more than 20 years old (most newer houses will have insulation already).
  • The walls are not exposed to driving rain.

If you have any damp patches on your internal walls then they should not be insulated until the problem is resolved. Speak to a builder who specialises in damp prevention.

If your home's external walls are joined to another house, the installer will need to insert a cavity barrier to contain the insulation so your neighbours aren't affected.

What is cavity wall insulation made from?

Cavity wall insulation can generally be made from three types of material: mineral wool, polystyrene beads, or foamed insulants.

All three are manufactured according to British standards. Foam insulation systems should be certified by the British Board of Agrément and installed according to strict guidance laid out in the associated certificates.

Are my cavity walls filled?

If your house was built in the last 20 years or so, the walls are probably insulated. To find out whether they are you can do the following: 

  • Ask a registered installer for a boroscope inspection. The installer will drill a small hole in your external wall to see if your walls are hollow or filled. 
  • Check with your local authority's building control department.

How is insulation installed?

To insulate your cavity walls, the installer drills small holes around 22mm in size at intervals of around 1m in the outside wall of your home. The installer then blows insulation into the cavity using special equipment. Once all the insulation is in, the installer fills the holes in the brickwork so you'll barely notice them.

Filling cavity walls is not a job you can do yourself, you will need to employ a registered installer. A professional can do the job in around two hours for an average house with easily accessible walls. It shouldn’t make any mess.

How do I find an installer?

Your installer should be a member of one of these organisations:

Remember to also check whether the installer is signed up to a code of professional practice like the one provided by the NIA and that the installation is guaranteed for 25 years by CIGA.

Your installer will suggest the most suitable type of insulation but check the installation is covered under CIGA, which means it complies with British standards. Ask your installer to ensure you make the best choice.

How much could I save?

England, Scotland and Wales



Semi detached

Mid terrace



Fuel bill savings (£/year)






Typical installation cost






Payback time

5 Years or fewer

Carbon dioxide savings (kgCO2/year)

 1,110 kg

 660 kg

 400 kg

 440 kg

 300 kg

These are estimated figures based on insulating a gas-heated home. The average installed cost is unsubsidised. Figures are based on fuel prices as of April 2018.

Northern Ireland



Semi detached

Mid terrace



Fuel bill savings (£/year) £215 £130 £80 £85 £60
Typical installation cost £720 £475 £370 £430 £330
Payback time 6 Years or fewer
Carbon dioxide savings (kgCO2/year) 1,370 kg 810 kg 510 kg 550 kg 380 kg

These are estimated figures based on insulating an oil-heated home. The average installed cost is unsubsidised. Figures are based on fuel prices as of April 2018.

I've problems with my cavity wall insulation. What should I do?

If you notice problems with your walls after having cavity wall insulation installed such as damp and mould, you should first call the company who carried out the installation. They should discuss the problem with you and revisit your property to establish whether the original survey or installation work is contributing to the problem. If it is, they should arrange for remedial work to fix the problem or for removal of the insulation if required.

If the installer is not willing to help or no longer exists then contact CIGA to establish whether you have a 25 year CIGA Guarantee. If you do, they should be able to help resolve the issue under the terms of the guarantee. If you don’t have a CIGA guarantee, check your paperwork from time of installation to see if you have an independent insurance backed guarantee which provides a similar level of cover. CIGA also have a contact form to report bad practice.

The symptoms of damp in a home can be very similar and could be caused by poor or inappropriate insulation, or by other issues such as inadequate home maintenance. Neither your installer nor a guarantee provider will agree to carry out or pay for remedial work if they determine that the problems were not caused by inappropriate insulation, bad workmanship or poor materials. If you believe your installer or guarantee provider is unreasonably refusing to help you, you should follow their complaints procedure.

If you are unable to get help from your installer or a guarantee provider, your final option is to speak to a company that can carry out the necessary work. We recommend that you use a company that is accredited with an appropriate scheme. If you are asking them to remove the insulation, you should use a specialist in cavity wall insulation removal accredited with a cavity wall insulation scheme such as CIGA or BBA.

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