Most homes built after 1920 have cavity walls. This means there are two layers of wall – the outer and the inner – with a gap between them. This gap, or cavity, is responsible for heat loss. The air in the cavity lets heat pass through the walls and out of the home.

What is cavity wall insulation?

To stop the heat from escaping through the walls, the cavity is filled in with insulation beads, foam, or mineral wool. You can think of it like a thermal vest between your skin and a jumper – an extra layer which helps keep the heat in.
To access the cavity, the installer drills small holes into the outer wall. The insulation is then pumped in. Once the cavity has been insulated, the installer will re-fill the holes that were drilled.

Is my home right for cavity wall insulation?

Firstly, you’ll need to check that your home has cavity walls. If your home is less than 100 years old, it’s likely to be the right type of construction.
If you have an Energy Performance Certificate, this will tell you whether your home has cavity walls. It will also say whether the cavity has already been insulated.

You might also be able to tell whether you have cavity walls by looking at the outside of your home. If you can see the brickwork, check how the bricks have been laid. If all the bricks look the same length, the wall is likely to have a cavity. If the bricks alternate between short and long, the wall is not likely to have a cavity.
If your home has cavity walls, it should be suitable for cavity wall insulation if:
– The cavity is at least 50mm wide
– The wall is in good condition
– There’s no rubble in the cavity
– The walls aren’t exposed to driving rain

Cost of cavity wall insulation

Cavity wall insulation typically costs around £20 per m2, making it the most cost-effective kind of wall insulation. The exact cost will vary depending on the material being used to insulate the cavity.

Regardless of the size of your home, cavity wall insulation should pay for itself within five years. This is because the amount you’ll save on your energy bills over five years should equal the cost of the insulation.

Grant funding is currently available for cavity wall insulation. For more information, see our Grant funding for cavity wall insulation section below.

Types of cavity wall insulation

There are several different kinds of materials which are used to insulate cavity walls. These wall cavity fillers vary according to cost, effectiveness and how environmentally friendly they are.

Blown mineral wool insulation

You may be familiar with mineral wool already – it’s commonly used in loft insulation and is sold in big yellow rolls.

Mineral wool is made in a similar way to candyfloss: a machine spins molten rock so that the fibres weave together.

With blown mineral wool insulation, tufts of mineral wool are blown into the cavity. They then knit together, forming an insulating layer.

Mineral wool is relatively cheap whilst also being effective. It can be recycled.

Polystyrene bead insulation

Polystyrene beads are blown into the cavity. These cavity wall insulation beads expand and bond together to ensure good coverage. Like blown mineral wool, polystyrene beads are relatively cheap whilst also being very effective.

Expanding foam insulation

Polyurethane foam is sprayed into the cavity. When this cavity wall insulation foam dries, it becomes solid. It is incredibly effective but also about twice the price of mineral wool or polystyrene bead insulation.

Removal of cavity wall insulation

If cavity wall insulation has been installed properly, there shouldn’t be any need to remove it. However, much of the cavity wall insulation installed during the 1980s was carried out with unsuitable materials or on unsuitable properties.

Incorrectly installed cavity wall insulation can mean that the insulation doesn’t keep your home as warm as it should. It can also cause issues with condensation and damp.

In cases such as these, the cavity wall insulation should be removed.

The company carrying out the cavity wall insulation removal will:
– Redrill the holes that the insulation was pumped in through
– Remove a brick from the bottom of your outer wall
– Use a vacuum to suck the insulation out from the hole at the bottom of the wall
– Pump air through the original holes to blow the insulation towards the vacuum. This makes sure the cavity is fully cleared

Cost of cavity wall insulation removal

The average cost to remove cavity wall insulation is £20 – £25 per m2. This will vary depending on the type of cavity wall insulation that’s being removed.

It may be possible to avoid the cost of removing cavity wall insulation. If mistakes were made during the installation or initial survey, the installer should arrange to fix the problem or remove the insulation for you. You should ask the installer to visit your home and check that everything was carried out correctly.

If the installer can’t help or has gone out of business, the work may still be covered by a CIGA guarantee. A standard CIGA guarantee is 25 years. You can contact CIGA to check whether your cavity wall insulation is still under guarantee.

If you don’t have a CIGA guarantee, check to see if the work is covered by any other kind of guarantee.
If the work was carried out before you lived in your home, check the Home Report for any guarantees. The Home Report should have been given to you when you moved in.

If neither CIGA nor the installer can help, you may need to pay for a company to remove the insulation for you. We’d recommend getting a quote from at least three different installers to make sure you’re getting the best price. You can use the National Insulation Associations’ search tool to find a company in your area.

Cavity Wall Insulation FAQ

Can I get cavity wall insulation if I live in a flat?

Yes, as long as all the flats above and below yours agree to get the insulation as well. The cavity runs the entire height of your block, so it’s not possible to fill just one section of it. The insulation would be pumped in at the top of the building and start to fill up from the bottom. You can think of it like pouring marbles into a pint glass. It’s not possible to just fill the top third or middle third of the glass – you have to fill the entire thing from the bottom.

Does cavity wall insulation cause damp?

There has been a lot of misinformation about cavity wall insulation causing damp. Cavity wall insulation in itself is very unlikely to result in damp. The vast majority of issues arise from bad practice on the part of installers.
This is why it’s important to always use an accredited insulation company. A responsible installer will make sure:
– Ventilation such as vents and airbricks are not blocked by the cavity insulation
– Any pre-existing issues with damp are sorted before cavity wall insulation is considered
– The cavity is free of rubble or debris
– The exterior of the walls is in good condition
– To check whether your property is exposed to high levels of wind-driven rain.

Is cavity wall insulation disruptive?

Cavity wall insulation is installed from the outside, so there’s no need for installers to enter your home.

Depending on the height of your home, scaffolding may be required. This will definitely be the case if you live in a flat.

The installer will drill a number of holes into the outer wall so that the insulation can be pumped in. There will be noise from both the drilling and the pump. The holes will be re-filled after the insulation has been installed.


Grant funding for cavity wall insulation

Grant funding for cavity wall insulation is available through our Home Energy Scotland service.

The Home Energy Scotland Grant offers homeowners up to £1,500 towards cavity wall insulation. An extra £500 is available through an optional interest-free loan.

To apply for Home Energy Scotland Grant funding, simply call their freephone number on 0808 808 2282 to speak to an advisor.