Cavity wall insulation

Cavity wall insulation can save you money

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Our helpful guide outlines everything you need to know about cavity wall insulation

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If your home isn’t insulated properly, the warmth can escape through the walls. According to the Energy Saving Trust, about a third of all the heat lost in an uninsulated home gets out through the walls.

But wall insulation can put a stop to this, and it doesn’t have to be expensive. It can also save you money on your energy bills. 

Do I need wall insulation?

You probably don’t need to worry about wall insulation if you live in a modern property, built in the 1990s or later, because your walls are likely to be insulated already. But you might want to insulate an older property – and that means you have to find out whether your home has solid or cavity walls.

Cavity walls

Houses built after the 1920s are likely to have cavity walls. A cavity wall is actually two walls with a gap – or cavity – in between. If you’re unsure, take a look at the brickwork. If the bricks form a regular pattern, chances are you have cavity walls. You could also measure the width of the wall. A wall that is more than 260mm thick probably has a cavity.

Cavity wall insulation fills the gap between the walls, helping to keep the warm air in, and helping to reduce any condensation inside the home.

It sounds like a big job, but the procedure is quite straightforward. The installer drills small holes in the walls and then pumps in insulating material, such as mineral wool, polystyrene beads or foam. When the work is done, the holes are filled in so they shouldn’t be noticeable. The whole process usually only takes a couple of hours.

You can only insulate cavity walls if they’re currently unfilled. If you’re not sure whether the walls are already insulated, you can ask a registered installer for a boroscope inspection. This involves drilling a small hole in an external wall, to see if the cavity is insulated or not. Alternatively, you could contact your council’s building control department to see if they have any information.

Is my property suitable?

Cavity wall insulation is not suitable for every property. The cavity must be at least 50mm wide and the installer must be able to reach all the external walls. If your house adjoins another property, the installer will insert a cavity barrier so your neighbours will not be affected.

Most companies insist that the brickwork is in good condition and not exposed to driving rain. You should also sort out any damp problems before fitting cavity wall insulation.

How much does cavity wall insulation cost?

The cost of cavity wall insulation varies, but you can expect to pay about £700 to insulate a detached house, or about £400 for a mid-terrace property. But the insulation could pay for itself within about five years because you could save up to £275 a year on your gas and electricity bills.

Make sure you choose the company you use carefully. Ideally, they should be a member of the National Insulation Association (NIA), the Cavity Insulation Guarantee Agency (CIGA) or the British Board of Agrément (BBA). You should also make sure the work is guaranteed for 25 years by CIGA.

Solid walls

If your home has solid walls, insulation is more complicated and more expensive. But, solid walls let through twice as much heat as cavity walls, so the savings on your energy bills could be greater. It can cost more than £20,000 to insulate solid walls and there can be considerable disruption to the household. But a detached home could save more than £450 a year on fuel bills.

Properties that were built before 1920 usually have solid walls. The brickwork pattern is irregular and the external walls typically measure less than 260mm thick.

To insulate solid walls, you can build a stud wall or fit rigid insulation boards to the internal walls. Or, you can fix a layer of insulation material to the external walls and then top with a protective render or decorative finish. Whatever you choose, it’s a good idea to make sure the insulation is covered by the 25-year Solid Wall Insulation Guarantee (SWIGA). The installer should also use materials that are certified by the BBA.

If your home is not made of bricks, but is a steel or timber frame building, you cannot fit cavity wall insulation but you might be able to insulate the walls as if they were solid. However, you will need to use a specialist company, and you should contact the NIA (

Do I need planning permission?

You don’t normally need planning permission for cavity wall insulation. But if you live in a listed building or in a conservation area, you might be subject to planning restrictions on any solid wall insulation.

Can I get financial help?

Lots of energy companies offer grants towards the cost of cavity wall insulation to eligible, low-income households. To apply, you also have to own your home or be a private tenant with permission from the landlord. Financial help is not usually available for solid wall insulation.

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