EXPERT ADVICE
Cavity wall insulation: Everything you need to know
Updated 07/26
By: Tom Blake
Reviewed: Kim Staples
Wondering whether you would benefit from having cavity wall insulation installed in your home? We'll answer all the common questions other people ask and help you to decide whether cavity wall insulation is something you want to explore.
What cavity wall insulation is and how it works
How to find out whether you have cavity walls
The benefits of cavity wall insulation
The different types available, and how to choose the best for your home
How to find a tradesperson to install your cavity wall insulation
How does cavity wall insulation work?
A cavity wall has two walls held together by wall ties with a gap between them. The gap is known as the cavity. The gap prevents rain from getting into the property through the outer wall.
So cavity wall insulation, as the name suggests, is insulating material that sits within that cavity.
It works by storing heat within the inner walls before bouncing it back into the room and retaining it for longer.
Because heat does not travel through the air very easily, it’s a natural insulator. The materials used to insulate cavity walls are chosen because they trap air between their fibres, creating what’s known as an ‘air matrix’. This means that insulated walls retain heat far more effectively than empty cavity walls.
The result? A warmer home with less wasted energy!
How is cavity wall insulation installed?
If you have cavity walls, the gaps in your walls can be insulated by injecting material in from the outside.
There's no need to break down the walls, or to damage them at all besides drilling a few holes.
Your installer will start by checking that the walls are suitable for insulation, ensuring they’re in good condition and that you don’t have any issues with damp.
If everything is in order, holes will be drilled in from the outside, at various points along the wall, and insulation is then injected through these holes. Once the walls have been filled, the holes are sealed over with cement.
Find a cavity wall insulation specialist near you
How do I know if I have cavity walls?
If you’re thinking of getting cavity wall insulation, the first thing you’ll need to do is work out if your property has cavity walls (as opposed to solid walls).
The age of your home is a great place to start. As a general rule, properties with cavity walls started being built in the 1920s and were a popular technique until building regulations changed in the mid-1980s.
Another clue is the appearance of your walls. If you have cavity walls, the bricks will usually be arranged in an even pattern, and all the bricks will be laid lengthways. If your bricks are arranged in an alternating pattern, producing rows of what looks like long and short bricks, chances are your walls are solid.
Of course, a tradesperson will be able to tell you for certain whether your property has cavity walls. They can check whether or not the walls are solid with what’s known as a borescope inspection, which involves drilling a small hole in your wall.
Alternatively, your local authority’s building control department might be able to help.
What if I have solid walls?
If your walls are solid rather than cavity walls, you'll need to explore other types of insulation.
That could be solid insulation boards (either external or internal), stud frames, a thermal lining, or other materials.
See our complete guide to planning your home insulation for more details and ideas.
Planning your home insulation
Upgrade your home insulation with our complete guide to this popular eco-home improvement project.
The benefits of having cavity wall insulation in your UK home
There is a wide range of benefits associated with cavity wall insulation. It’s one of the most cost-effective home improvements out there.
Lower energy bills
With cavity wall insulation, the savings you will make on your energy bills are significant. So much so, that the cost of the work usually pays for itself in less than five years.
A warmer home
A third of all heat that escapes from your home does so through the walls. Cavity wall insulation helps to prevent it.
Reduced carbon footprint
When your heating escapes through the walls, you’ll need to use more energy to heat your home. Cavity wall insulation prevents the escape of energy, meaning you’ll use less energy and, as a result, lower your carbon footprint.
Quick and easy installation
Although you’ll need a professional to carry out the work for you, the actual process of installing cavity wall insulation is relatively quick, easy and disruption-free. It can normally be completed within two hours, depending on the size of your property, of course.
Find a cavity wall insulation specialist near you
Types of cavity wall insulation
The best type of cavity wall insulation for your property will depend on several things, including how thick your wall cavities are, the degree of humidity and the atmosphere in your property, and your budget.
The most popular and common materials to use for this type of insulation are:
Blown mineral fibre
Blown mineral fibre is one of the most common types of cavity wall insulation. It consists of strands of fibreglass or mineral wool, which are then forced into the wall cavity using compressed air. These fibres then expand to fill out the space.
Mineral fibre is similar to the quilt insulation used in lofts. For walls, it is broken down into small tufts to allow it to be blown in.
This type of insulation is covered by the British Board of Agrément (BBA) Certificates and can be used anywhere in the country.
Pros:
This is a relatively cost-effective insulation method, and it’s easy to install. As a result, it is often used by free cavity wall insulation schemes.
Cons:
Blown mineral fibre can only be used for standard sized or wide cavities as, if it’s used in cavities under 50mm, there is a risk of it becoming patchy.
It’s also important that it is correctly installed to avoid problems further down the line.
It must be kept totally dry to avoid it losing its insulating properties.
Polystyrene beads and granules
EPS beads and granules are blown into the cavity using compressed air with a mix of adhesive. When the adhesive cures, it bonds the beads together and creates an insulated barrier within the wall cavity.
The beads can be supplied loose or in a light resin to hold them together. Or, if you’re using granules, these will stick together on their own, thanks to their shape.
This type of insulation is usually used in walls with a narrower cavity.
Polystyrene beads are covered by the British Board of Agréments (BBA) Certificates.
Pros:
It is very effective at trapping heat and creating really solid cavity wall insulation free from gaps.
It also allows any moisture to drain through to the ground, helping to prevent damp.
Cons:
It has been known for loose granules to escape through the airbricks, particularly if you have work done on your property at a later date that requires the walls to be cut or drilled into.
Foam
This type of insulation is pumped into the cavity. The foam is created instantly within the wall cavity when two chemical components are injected and mixed.
Polyurethane foam can be injected into the wall cavity through small holes, achieving results that should last as long as the life of the building without any further maintenance.
How much does cavity wall insulation cost to install?
As a general rule, you can expect to pay around £30 - £65 per m². This is based on polyurethane foam.
You're best off talking to your local cavity wall insulation installers to get an accurate quote.
Check out our cavity wall insulation cost guide for more information.
How much does cavity wall insulation cost in 2026?
Cavity wall insulation can improve your home’s energy efficiency and reduce your energy bills. But how much does it cost? Here’s the lowdown.
Find a cavity wall insulation installer near you
To get started finding a tradesperson to install your cavity wall insulation, all you need to do is enter your postcode. Then you can browse tradespeople working in your area, compare your options, and reach out to gather quotes.
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Or you can request a quote by posting your job to hear back from available installers - or download the Checkatrade app.
FAQs
Cavity wall insulation costs around £2,700 overall for an average semi-detached property. See more details in our guide to cavity wall insulation costs.
Yes, cavity wall insulation is highly recommended for suitable homes, including by the Energy Saving Trust. However, it isn't recommended for homes that are prone to severe damp or flooding.
Some of the disadvantages of cavity wall insulation are:
It can increase damp in your home if it gets wet, such as through flooding
Some insulating materials can degrade over time
It can damage airbricks and trickle vents if not installed correctly
It's expensive to remove
Yes, cavity wall insulation can be removed easily without damaging your walls. See our guide to cavity wall insulation removal costs to see how much it may cost you.
Yes, there is evidence that good insulation in your home - including properly installed cavity wall insulation - can increase its value. It can also contribute to a higher EPC rating and lower energy bills.
Cavity wall insulation should last between 25 and 40+ years when installed properly - it's designed to be a long-term solution for your home.
Need help with your home insulation? At Checkatrade we have a number of resources to help with your decisions, such as eco-friendly choices and planning guides.
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