Mould after cavity wall insulation

September 29, 2021
Mould cause by cavity

In many properties, cavity wall insulation can help save energy and cut fuel bills. But what should you consider before making the decision to have it installed in your home? And what should you expect from a reputable installer?

With the help of RICS chartered surveyor Tim Davies, we've put together a checklist of things to look out for throughout the cavity wall insulation process, to help you spot potential problems early.

Before the survey:

How old is your house and do you have cavity walls?

If your home was built in the last 10 years it is likely that the cavity is already insulated. Most cavity walls are in houses built from the 1920s onwards. Use this Energy Saving Trust guide to tell if your house has cavity walls.

Where is your house situated?
If the walls of your home are regularly exposed to wind-driven rain, they may be unsuitable for cavity wall insulation. Some houses are more exposed to the elements than others, for example, if they are on a hill or by the coast. South-westerly facing properties are most susceptible.

Do you have damp problems?

Not everyone who has damp problems is aware of them, but if you already have issues with damp, cavity wall insulation can make the problems worse. If you have damp walls, black mould or fungus problems or water ingress, or if your home smells damp and musty, you should get a professional to advise on whether you have damp.

Are there cracks or damage to the outside walls?

If the walls of your home are not in good condition, rainwater can penetrate the outside wall and make the insulation (and the inside of the house) damp. The house should be in good repair before cavity wall insulation is installed.

During the survey:

Did the surveyor look both inside and outside the property?
A proper survey should be more than a quick ten minute walk around the outside of the house. The surveyor should look inside and out and consider all the potential problems, as well as making thorough notes on what the installer should bring (amounts of insulation, vents, airbricks, brushes to separate off neighbouring properties with adjoining walls etc).

Did they drill a hole in the wall and look inside using a cavity camera?
This is to see whether there is already insulation in the property, but also to see if the cavity is clear. If there is rubble in the cavity or if there are mortar droppings on the wall ties, this can stop cavity wall insulation going into the walls evenly. If there are gaps, these can cause cold spots which can lead to damp problems.

Did they ask questions about damp problems in your home?
See above. If you already have issues with damp, cavity wall insulation can make the problems worse.

Did they note vents, boiler flues, driveway levels, open fires, oblique chimney breasts and timber-suspended floors?
These can affect both whether the installation can go ahead and the way it is carried out.

After the installation:

Are you getting damp patches, black mould, oblique condensation? Is the house noticeably colder than before?
All these are warning signs that either the house was unsuitable or that the installation was not successful. In the first instance, contact the company who installed the insulation. If they are not able to resolve the problems, and your installation was done by a company which is registered with

CIGA (the Cavity Insulation Guarantee Agency)
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