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Cavity wall insulation problems: what to do if yours has failed and how it affects a sale

Suspect faulty cavity wall insulation? The GOV.UK steps: installer first, then the cover provider, how to treat claims firms, and what to tell a buyer.

3 min read
Last reviewed 4 November 2026
By Your Property Check team

Part 1 of 5

Start with the paperwork

General information, not advice. This page covers what official guidance says to do about suspected cavity wall insulation (CWI) problems, and how that can matter if you sell. The main source is a GOV.UK consumer guide dated October 2019, plus current GOV.UK guidance on poor quality wall insulation, both read on 4 November 2026. The 2019 guide says most cavity wall insulation has been completed in suitable homes to good standards, and that genuine problems have arisen in a small number of cases.

Part 2 of 5

The steps official guidance gives

The 2019 guide is for homes where CWI was installed under the Green Deal or the Energy Company Obligation (ECO). It says that if you suspect the installation has failed, or you are unsure whether it has caused condensation or mould, you should:

Contact the installer who did the work, in the first instance. The installer should contact you, investigate and promptly put right any defects.
If the installer has gone out of business or has not dealt with it, contact the cover provider. The guide says the provider details and the paperwork should have been given to you at installation.
Look up the provider. For ECO work, the guide points to Ofgem's list of providers. It also names the National Insulation Association and CIGA, which issues cover for CWI fitted in the UK and Channel Islands, and says CIGA support is available only to consumers who hold CIGA cover.

Separate current GOV.UK guidance covers insulation fitted under the Great British Insulation Scheme or ECO4. It says that if the work is found to be faulty, your installer will be asked to fix it, and you should not be asked to pay for that work. It says Ofgem, TrustMark or a certification body may contact you, and gives a freephone number for checking a caller is genuine.

Part 3 of 5

What to check at home

Sign	Possible cause	First step	Document to keep
Condensation or mould on walls	The 2019 guide says installation may have caused it; there can be other causes	Photograph it and contact the installer	Installation paperwork and photographs
Installer no longer trading	Business closed	Contact the cover provider named in your paperwork	The cover document given at install
Letter from Ofgem about your insulation	Quality checks on GBIS or ECO4 work	Follow the letter and give your reference number	The letter and your reference
Unsolicited call about a claim	A claims management company	Follow the checklist below	Notes of who called

Only a qualified surveyor can say what is causing damp or mould in a particular home. Our survey decoder helps you read what a survey report says.

Part 4 of 5

Be careful with claims firms

The 2019 guide warns that claims management companies and solicitors have contacted householders, offering to act for compensation, and that some of these cases are not genuine. It suggests that you:

check identification and company credentials before letting a caller in;
ask for a clear explanation of any charges, commissions and fees, including opt-out fees, in writing where possible;
avoid giving personal details, financial information or your insulation paperwork to a cold caller;
decline to sign anything on your doorstep;
report suspicious activity to the cover provider, Trading Standards or Citizens Advice.

Part 5 of 5

How it can affect a sale

Insulation problems can come up in a buyer's survey. A buyer is likely to ask what was installed, when, by whom and what paperwork exists. That is why the cover document and installer details matter. We found no official source on how much a problem changes a sale price, and no source for removal costs, so we give neither.

The EPC is a separate matter. Citizens Advice says you must provide an energy performance certificate free of charge to potential buyers, and that it is valid for ten years. Our guide to finding an EPC and the EPC finder show how to check yours. For other building problems that can arise in a sale, see our subsidence guide.

If you are selling, deal with the installer or cover provider first where there is a live issue, and tell your conveyancer what you know so the property information forms are answered accurately. This page is general information, not advice.

Our take

Keep the cavity wall paperwork where you can find it

Our view: the paperwork is the part of a cavity wall insulation problem you can control. Contact the installer or cover provider first, keep the cover document and any letters, and tell your conveyancer what you know so the forms are answered accurately. The common mistake is hearing nothing about it until a buyer's survey raises it.

What Your Property Check adds: our free house valuation gives an honest value range from real HM Land Registry sold prices in your postcode, with the comparable sales and the working shown, so you can see where the home stands before you decide how to sell. No email or phone needed.

Check my value

Our opinion, drawn from the facts on this page: not advice and not a forecast. We earn from OfferCheck reports and from introducing sellers to cash buyers, so weigh it with that in mind (see our disclosure). We are not authorised or regulated by the FCA.

Questions, answered

Frequently asked questions

What are the signs of faulty cavity wall insulation?

The GOV.UK guide we read names condensation or mould that may have been caused by the installation. These can have other causes, so ask a qualified surveyor to find the cause in your home.

Is there cover for it?

The 2019 GOV.UK guide says the cover provider and paperwork should have been given to you at installation. If the installer has gone out of business or has not acted, contact that provider.

Can you claim?

The route in the GOV.UK guide is installer first, then the cover provider. It warns about claims management companies and says some cases are not genuine, so research any firm before agreeing to anything.

Will it stop a sale?

We found no official source saying so. A buyer's survey may raise it, so keep your installation paperwork and tell your conveyancer what you know.

Who pays if the work was faulty?

For work under GBIS or ECO4, GOV.UK says the installer will be asked to fix faulty work and you should not be asked to pay. For older work, follow the installer then cover provider steps.

Where this comes from

Sources

Last reviewed 4 November 2026 by the Your Property Check team. This page is general information, not legal, tax or financial advice. For your own situation, speak to a conveyancing solicitor or another qualified professional.