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Home & garden.

Updated: 30 Jun 2021

Cavity wall insulation FAQs

We've asked the experts to fill you in on the most common cavity-wall insulation questions.
Which?Editorial team
Familyhome 450341

How much does wall insulation cost?

The cost of insulating your property’s walls depends on the size of your home, whether the walls are cavity or solid and the condition they’re in.

You’ll find a guide to the approximate costs and savings involved in installing the different types of wall insulation in our guides to cavity wall insulation costs and savings and solid wall insulation

Installing wall insulation is one of the most cost-effective improvements you can make to your home. The savings you make on your heating bills means insulation could pay for itself in as little as nine months.

Don't pay over the odds to heat your home. Use our independent energy switching service, Which? Switch, to look for a cheap energy deal.

Does my house have cavity walls?

The picture above shows a solid wall (left) and a cavity wall (right). The brick pattern can often be an indication of the type of wall you might have. 

Solid walls tend to be fortified with bricks laid across, rather than along, the wall. These will look like smaller, half-sized bricks from the front. A cavity wall will have all the bricks laid in the same direction, so they'll all look the same size. 

If your home was built from 1920 onwards, it’s likely to have cavity walls. To be suitable for cavity wall insulation, the cavity should be at least 50mm wide and the walls need to be in good condition. 

If your house was built in the past 20 years, it’s likely that the cavity walls were insulated when they were built.

Can I get financial help to pay for cavity wall insulation?

Maybe. Under the Energy Company Obligation, some households are eligible for discounted or free insulation, but the eligibility criteria is complex and depends on the condition your property is in. 

Visit the government-run website Simple Energy Advice to see if you could be eligible. 

Can cavity-filled walls become damp?

Wall cavities are designed to catch rain coming through the outer walls and divert it away from the inside of your property, so if cavity wall insulation is poorly fitted or used in the wrong place, it can cause damp problems.

But provided the insulation material is water-repellent and is installed correctly, damp shouldn’t be an issue.

Any installer registered with the Cavity Insulation Guarantee Agency (CIGA) should check whether your home is suitable. Their work and materials will be covered by a 25-year guarantee.

Some cavity walls are not suitable for cavity-wall insulation, including those regularly exposed to wind-driven rain.

In early 2011, Which? uncovered some bad practice when it came to getting advice about cavity-wall insulation for a house prone to damp. Visit our guide to damp problems in cavity walls for details. 

Do I need planning permission for cavity wall insulation?

Planning permission is not normally required for wall insulation.

However, if your property is listed, is in a conservation area or the insulation will change the appearance of your property, you should consult your local planning authority.

Where can I find a wall insulation installer?

For cavity-wall insulation, choose an installer registered with one of the following organisations:

  • The National Insulation Association (NIA)
  • The Cavity Insulation Guarantee Agency (CIGA)
  • The British Board of Agrément (BBA).

You should check that your installer has signed up to a code of professional practice, such as that offered by the NIA, and make sure the insulation installation is guaranteed for 25 years by the Cavity Insulation Guarantee Agency (CIGA).

The CIGA provides independent 25-year guarantees for cavity wall insulation fitted by registered installers in the UK and Channel Islands.

Visit Which? Trusted Traders to find local insulation installers that have been vetted by Which? 

You can also use our Trusted Traders search tool above to find local fitters near you.

What other types of insulation could reduce my heating bills?

There are plenty of ways to improve your home's insulation and reduce your energy bills:

  • Insulate your loft to save up to £215 a year.
  • Buy jackets to fit around your hot water cylinder and piping. These are available from DIY stores and can be fitted yourself, provided that your pipes are easily accessible. The energy savings are small but, as jackets cost about £15, they'll pay for themselves in a year or so.
  • Fit draught excluders to doors, windows and letterboxes to reduce heat loss. Gaps between skirting boards and floorboards are also worth tackling. 
  • Install curtains and remember to close them at dusk to stop heat escaping overnight.
  • Double glazing reduces heat loss and noise and can help with condensation problems. You can expect savings of up to £110 a year on bills if you replace whole-house single glazing with double glazing. Make sure you use a company you can trust – we've found the best and worst double glazing companies.

To cut your fuel bills further, make sure you're on the right energy tariff. Using our independent not-for-profit switching site, Which? Switch, tocompare gas and electricity prices.