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Last updated on April 29th, 2024

Cavity wall insulation cost guide

Keeping your home warm and toasty can be challenging, not to mention costly. Did you know that if your home isn’t properly insulated, approximately one-third of all heat lost escapes through your walls?

Looking for ways to reduce heat loss from your property? Cavity wall insulation could be the answer. If you live in an older property built before the 1990s, you likely have cavity walls. In that case, you can save huge amounts of energy, keep your heating bills down and ensure your home is warm and comfortable by installing cavity wall insulation.

Here’s everything you need to know about cavity wall insulation and a handy price guide to give you an insight into how much you’ll need to spend.

How much does cavity wall insulation cost?

Example property typeAverage price
Detached property£3,200
Semi-detached property£2,700

Our costs are ballpark averages – get a local tradesperson to quote now

The costs of cavity wall insulation will vary depending on several factors, particularly the size of your home.

Before any cavity wall insulation is installed, your walls must be inspected to check they are suitable. Any issues, such as damp or other wall defects, will need to be addressed before the work is started.

Costs may vary by region, the scope of the project and indeed by the products you plan to use. You’ll need to take this work into account in your budget.

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Cavity wall insulation cost per m2

The cost of cavity wall insulation depends on your property’s size, the accessibility of the walls, the type of insulation you choose, and the installer you work with.

As a general rule, you can expect to pay around £30 - £65 per m². This is based on polyurethane foam. Glass wool will be cheaper at around £25 - £30 per m².

It’s worth bearing in mind that whatever the size and type of your property, you should be able to recoup the costs of cavity wall insulation in under five years, thanks to the savings you’ll make on your energy bills.

Can I get free cavity wall insulation?

The government have recently announced The Great British Insulation Scheme which offers free or cheaper insulation to reduce your home’s energy bills. You may be able to get support to install cavity wall insulation as well as:

  • Solid wall insulation (internal or external)
  • Loft insulation
  • Flat or pitched roof insulation
  • Underfloor insulation
  • Solid floor insulation
  • Park home insulation
  • Room-in-roof insulation

You might get support if your home has an EPC of D-G, or your home is in a council tax band A-D in England or A-E in Scotland or Wales.

You can check on their website to see if you’re eligible for support.

How does cavity wall insulation work?

A cavity wall comprises two thin walls held together by wall ties, with a gap between them. Known as the cavity, this gap prevents rain from getting into the property through the outer wall.

Cavity wall insulation works by storing heat within the inner walls before bouncing it back into the room and retaining it for longer. The result? A warmer home with less wasted energy!

But how does cavity wall insulation actually work? Because heat does not travel through the air very easily, it’s a natural insulator. The materials used to insulate cavity walls per m2 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.

How will my cavity walls be insulated?

If you have cavity walls, the gaps in your walls can be insulated by injecting material in from the outside.

Your trader will check that the walls are suitable before 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.

benefits of cavity wall insulation

Do I have cavity walls?

Properties in the UK have either solid walls or cavity walls. As the name suggests, you can only have cavity wall insulation if you have cavity walls.

So, if you’re thinking of getting cavity wall insulation, the first thing you’ll need to do is establish if your property has cavity 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 professional trader 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.

The benefits of having cavity wall insulation in your UK home

There is a wide range of benefits associated with cavity wall insulation. In fact, 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.

Types of cavity wall insulation

There are several different types of cavity wall insulation. 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 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.

However, it’s not without its downsides. 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.

Mineral fibre must be kept totally dry to avoid it losing its insulating properties.

This type of insulation is covered by the British Board of Agrément (BBA) Certificates and can be used anywhere in the country.

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. It is very effective at trapping heat and creating really solid cavity wall insulation free from gaps. Another benefit of this type of insulation is that it allows any moisture to drain through to the ground, helping to prevent damp.

However, 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.

Polystyrene beads are covered by the British Board of Agréments (BBA) Certificates.

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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.

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.

Cavity wall insulation calculator

A cavity wall insulation cost calculator will provide a rough guide on how much you should be paying to have your cavity wall insulation installed. Simply enter the length and height of the wall in metres, and the calculator will do the maths and give you an average cost.

Cavity wall insulation isn’t a job you can do yourself. You will need to contact a professional, registered installer to carry out the work.

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cavity wall insulation removal cost

Cavity wall insulation FAQs

How long does it take to insulate cavity walls?

It should take an experienced professional around two hours to insulate cavity walls in an average house with easily accessible walls as a rough guide.

How much does it cost to remove cavity wall insulation?

For detailed prices please read our comprehensive cavity wall insulation removal cost guide. Costs start from around £1,680 for a typical semi-detached home. If you have cavity wall insulation that has not been installed properly by a qualified professional, you may need to remove it for these reasons:

  • The insulation was completed with unsuitable material
  • The wall cavities aren’t wide enough for insulation, leading to damp issues
  • The insulation was installed incorrectly
  • Your property has timber frames, so cavity wall insulation should never have been installed
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