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Last updated: 14 June 2024

Cavity Wall Insulation Problems

For homeowners, cavity wall insulation is a popular method of keeping in heat and decreasing monthly bills. It is known to save energy, and there are government schemes providing a range of funding to cover some of the cost of installation for eligible people.

However, cavity wall insulation can cause problems such as cold spots, rain penetration, damp, and even black mould. So how do these problems occur, and how can you avoid them in your home?

How Do Cavity Wall Insulation Problems Occur

There are a number of different reasons why an issue with cavity wall insulation can occur in your home. However, the key problems to watch out for are water penetration, and the use of outdated materials. If either of these things apply to you, it’s recommended to seek professional advice and make some home improvements.

Retrofit cavity wall insulation

If you own an old house that was not designed to accommodate cavity wall insulation, this creates a risk. Older houses have a bit less space between the outer and inner walls, which makes retrofitting risky. If it is not done correctly, the insulation can become damp and attract mould as a result.

Retrofit issues are common

It’s such a common problem that the Building Research Establishment (BRE) has put together a report about the unintended negative consequences of retrofit cavity wall insulation in Wales, and their advice for the future.

Poor installation

If your cavity wall insulation is not sealed from the outside properly there will be holes that the water can get in through. This can cause a whole host of issues by allowing rain to get past the brickwork and into your house. Over time, this results in the insulation becoming saturated with moisture, which can pass through to the interior walls in your home.

Shoddy workmanship

If you hire someone who carries out the job poorly, things can quickly go from bad to worse. Not only will you have to pay to have the cavities refilled, but your bills will also go up, and you will have to pay for repairs to damaged things in your home.

Hire someone who is Cavity Insulation Guarantee Agency (CIGA) accredited

It’s recommended to hire a practitioner who is accredited by the CIGA, who can give you the best service and advice in line with industry standards.

Outdated insulation material

In the late 20th century, many houses in Britain were fitted with cavity wall insulation made from fibreglass or formaldehyde. Both materials have since proven to be ineffective.


Formaldehyde shrinks over time, decreasing its effectiveness and leading to cold bridging. Even worse, it is known to give off toxic fumes which present a health risk.


Fibreglass, on the other hand, is susceptible to moisture. While its insulation properties are sound, if it comes into contact with rain, it will become useless and will introduce moisture into your home.

Increased energy bills

As well as leading to mould, this will cause your heating bills to rise until the problem is rectified.

EPS beads

Instead of these outdated solutions, it’s recommended to use polystyrene beads, also known as EPS beads. All reputable insulation companies will use this method, which is a much more durable method of insulating your cavity walls.

Cavity Wall Insulation Can Lead To Damp

Cavity wall insulation on its own cannot cause damp. However, as we’ve seen above, if cavity insulation is carried out poorly or installed on a home that’s not suited for it, this can certainly lead to damp. Additionally, if the materials used are of poor quality, this can worsen the issue. Here are a few risk factors that could increase the chance of your insulation becoming damp.

Your home is exposed to severe rain

If you live in a part of the country that frequently experiences severe rain, your house could be more at risk. The more rain that comes into contact with your home, the higher the risk of it penetrating the brick wall.

Your home isn’t sheltered

If your house isn’t surrounded by cover from things like trees, hills, or other buildings, you’ll be at a higher risk of damp with your cavity wall insulation. This is because more moisture is able to come into contact with your house, increasing the likelihood of a problem occurring.

Brickwork is poorly maintained

If the outer walls of your property are cracked and damaged, you may have holes running directly through to the cavity walls. This is a huge problem because it will allow moisture into your home, leading to potential issues with damp.

Cavity Wall Insulation Can Damage Your Property

Put simply, if your cavity wall insulation is installed incorrectly, or you used outdated materials instead of EPS beads, you may be at risk of moisture entering your home. Here are some things to be aware of.

Types of damage homeowners should be aware of

If you are experiencing any problems, you should contact the Property Care Association who can survey your home for damage caused by cavity wall breaches, such as condensation and damp. Here are a few things that can be damaged if your cavity wall insulation fails.

Damage to inner walls and structure

The most common problem caused by faulty cavity walls is damage to the inner walls of your home. This can also extend to structural parts of your home such as the floorboards or skirting boards.

Damage to property

If any of your things come into contact with a damp wall caused by cavity wall insulation, this can make your them damp and cause them to go foul.

Damage to furniture

Since furniture is often pushed up against a wall, it is at risk if you experience a cavity wall failure. Exposing furniture to damp can damage it beyond repair.

Does Cavity Wall Insulation Deteriorate Over Time?

In a theory, cavity wall insulation should not deteriorate over time. However, as we’ve seen throughout this article, if insulation materials become exposed to water, this can lead to all sorts of problems.

Regularly check your insulation

Get into the habit of checking the cavity insulation at your property regularly, so you can spot things that don’t look right and stop any problems before they occur.

What Are The Disadvantages Of Cavity Wall Insulation

Moisture and damp aren’t the only things you need to think about when it comes to cavity walls, there are many other disadvantages.


Cavity wall insulation is not something you can figure out for yourself over the weekend. You’ll need to get a quality practitioner in, which isn’t cheap.

Potential installation problems

This article has discussed the potential pitfalls of installation leading to water breaches, however, incorrectly installed insulation can also lead to inefficient heating, resulting in a higher energy bill.

Cold spots

Cold areas are one of those things that you may not immediately flag as an insulation issue. But if part of your house is particularly cold, or there is condensation on a specific patch of wall, this could be the reason why.

Some properties aren’t suited for it

Not every property is suited to cavity wall insulation. If you’re unsure whether your home is suitable, seek advice from a professional.

Buildings with no cavity

If your walls don’t have cavities, there’s nowhere for the insulation materials to go. If this is the case, you’ll have to find a different way to insulate your house.

Homes with a cavity that’s too small

If your house has cavity walls but they’re particularly small, filling them with insulation is likely to result in damp inner walls should any moisture find its way in.

How To Make Cavity Walls Work For You

Hire a professional

Don’t be tempted to do a deal with someone who can’t provide the right services. Hire a professional who will do a quality job. Also, look into government schemes that can provide funding for cavity wall insulation. If there’s a programme you’re eligible for, you’ll be able to save money.

Check your insulation regularly

Many serious problems with insulation occur because the homeowner doesn’t inspect it often enough.

Check your outer walls for breaches

The source of a breach is almost always on the outer walls, so inspect them regularly to see where water could potentially get in.

Check the material

Find out what your insulation is made of. If it’s made from formaldehyde or fibreglass, it’s time to get it refitted with a more modern product.

Look at other solutions

If your house isn’t suited to cavity wall insulation, it’s worth having a look at other services that are available. There are many other things you can do to insulate your property

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