Help reduce heat loss in your home with by filling the gap in your external walls.
According to our research, about 33% of all the heat lost in an uninsulated home escapes through the walls. By installing cavity wall insulation, you can save energy and reduce your heating bill.
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 might not have any wall insulation.
Here’s our guide on cavity wall insulation: what it is, if it’s suitable for your home, its benefits and how to get it.
The Warm Homes Plan is set to invest close to £15 billion in improving the UK’s homes to cut energy bills.
For people on low incomes, there’ll be fully funded government support to install insulation.
There’ll also be low and zero-interest loans available for homeowners regardless of income.
We’ll update this guide when we know more.
For more information, read our blog on what the Warm Homes Plan means for you.
Wall insulation is an extra layer that can help keep more heat inside your home. Cavity wall insulation is where material is injected into the space between the two layers that make up your external wall (known as the cavity).
Before you can insulate your walls, you need to find out what sort of wall you have. Houses in the UK mostly have either solid walls or cavity walls.
If your house was built after the 1920s, its external walls are probably cavity walls. A cavity wall is made up of two masonry walls with a gap in between them. The outer layer is usually made of brick, while the inner layer will be made of brick or concrete block.
Pre-1920 older houses are more likely to have solid walls. A solid wall has no cavity: each wall is a single solid wall, usually made of brick or stone.
Find out more about solid wall insulation.
Some older houses do have cavities in the wall, but these are usually too narrow to insulate. These walls should be treated as if they were solid walls.
If you’re thinking about insulating your walls, the first thing you need to find out is what type of walls you have.
If your home is made of brickwork that’s visible on the outside, 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. Some bricks will be laid across the wall so you can see the smaller ends from the outside.
If your walls are covered (for example with render or timber cladding), you should get advice from a building professional.
You might get a better idea of what type of wall it is by measuring its width. You can do this by measuring the wall thickness from the inside of an open door or window to the outside.
Some houses will have a different type of wall structure altogether, such as:
If your walls are timber framed, the frame will likely be on show somewhere. However, it could be covered with render, cladding, or a newer masonry facing.
If you’re unsure what type of walls you have then it’s best to ask a specialist installer or other buildings professional. This could be an architect or surveyor. If they have experience of insulating your building type, they can also suggest options for how to add insulation.
Cavity wall insulation is suitable for many homes. Many people have no issues following cavity wall insulation installation.
But cavity wall insulation might not be suitable if your home is:
These risks should be assessed by your installer or buildings professional.
It’s very important that any repair and maintenance to the exterior of your building is completed before any wall insulation is added. This includes:
If you don’t, you might trap damp or the insulation may fail.
Insulating your cavity walls can:
The cost of installing cavity wall insulation will depend on the size of your home. However, it’ll likely take only five years or less to make back the cost through the money saved yearly on energy bills.
Installing cavity wall insulation for a typical home in Great Britain (GB) can cost around £2,700. In Northern Ireland (NI), it can cost around £1,000.
If you’re already making home improvements, you might be able to reduce installation costs by carrying out the work at the same time. You could also push some jobs back if insulation is a priority.
You might be able to get funding or grants for insulation. Find financial support for energy efficiency in your area.
Cavity wall insulation shouldn’t cause damp if installed correctly.
An installer should check that your building is not exposed to extreme weather or flooding. They’ll also check if it has a narrow cavity, where installing cavity insulation could lead to water ingress. They should advise against getting cavity wall insulation if this is the case.
Air needs to flow in and out of your house so it stays fresh, dry and healthy. It also helps prevent the build-up of moisture and damp in your home.
A good installer should also not to block or seal any intentional ventilation such as:
If you notice problems like damp or mould after having cavity wall insulation installed, you should first call the company who carried out the installation.
They should discuss the problem with you and revisit your property to carry out checks. This will help them figure out whether the original survey or installation work is part of the problem. If there are issues with the work, they should arrange to fix the problem or remove the insulation if required.
If the installer isn’t willing to help or no longer exists, then check your paperwork. You need to find out if you have a guarantee certificate from the Cavity Insulation Guarantee Agency (CIGA). If you do, they should be able to help resolve the issue under the terms of the guarantee. CIGA also have a contact form to report bad practice.
If you don’t have a CIGA guarantee, check whether you have an independent insurance backed guarantee which provides a similar level of cover.
Damp could be caused by poor or inappropriate insulation. But it can also be caused by other issues such as inadequate home maintenance.
If damp is caused by inadequate home maintenance, neither your installer or a guarantor will agree to carry out or pay for remedial work.
If you believe your installer or guarantee provider is being unreasonable by refusing to help you, you should follow their complaints procedure.
Unable to get any help from your installer or a guarantee provider? You could get an independent assessment of the walls from a buildings surveyor. You can find one via Royal Institution of Chartered Surveyors (RICS)
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 need to remove the insulation, you should use a specialist cavity wall insulation removal company.
How suitable cavity wall insulation is for you is down to your circumstances, how your home is constructed and its condition. However, it can help keep your home warm, reducing your reliance on heating, and therefore lower your energy bills.
It also helps tackle carbon emissions and is a relatively unintrusive home improvement that could be covered by government schemes.
Insulating cavity walls is not a job you can do yourself: you’ll need to hire a registered installer. For an average home with easy-to-access walls, they’ll usually be able to do the job in about two hours and shouldn’t make any mess.
If your house was built in the last 20 years or so, the walls are probably already insulated. To check for cavity wall insulation in older properties you can either:
You can find a TrustMark-certified insulation installer. TrustMark is a government-endorsed quality assurance scheme for work done in and around your home.
Alongside checking if the installer is signed up to a code of professional practice, you should check the guarantee or warranty for their work. Installation work should be guaranteed for 25 years by the Cavity Insulation Guarantee Agency (CIGA) or have an independent insurance-backed guarantee.
You’ll need an installer to carry out a survey to check it’s suitable for cavity wall insulation.
Your home will be suitable for standard cavity wall insulation if:
If your house is suitable, the installer will then be able to insulate your walls using a suitable material such as polystyrene beads.
It’s not recommended to have cavity wall insulated if your home:.
This is because it could lead to damp problems.
If you have any damp patches on your internal walls, don’t insulate them until the source of dampness is resolved.
If your home’s external walls are joined to another house, the installer will need to insert a cavity barrier to contain the insulation. This is to make sure the insulation doesn’t affect your neighbours.
If you live in a flat, then you won’t be able to have just your flat insulated. You’ll need to speak to the building owner and get agreement from everyone to insulate the whole block.
Many cavity walls can be insulated by injecting insulation material into the cavity from the outside.
During the process, the installer will:
First, 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 the insulation material into the cavity using special equipment.
Once all the insulation is in, the installer fills the holes in the brickwork.
If the filler material doesn’t match the colour of the brickwork or render, you may still notice where the holes were. But you can easily paint over these afterwards.
As well as insulating cavity walls, you can insulate other areas of your home to reduce heat loss and save money.
Find out about other types of insulation and other energy efficiency measures.
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Last updated: 8 May 2026
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