Identifying cavity wall insulation problems

12th November 2024

Poorly installed cavity wall insulation can cause problems. In July 2020 the Chancellor announced a Green Homes Grant to give up to £5,000 in vouchers for insulation (BBC News, July 2020)

A few years ago, we wrote this article about the problems (usually damp) associated with cavity wall insulation. At the time it was thought the issue could be widespread as numerous news articles demonstrated. One newspaper reported: : “1.5 million homes are blighted by damp after cowboy builders cash in on a Government insulation drive”. Another asked: “Could the cavity-wall insulation scandal rival PPI?”.

As funding is now available for homeowners, we wanted to make sure that you didn’t fall foul of the same issues that have occurred in the past.

What is a cavity wall?

Many post war properties (and quite a few pre-war properties) were constructed with external cavity walls. These comprise:

An outer leaf (usually brickwork)
A gap
An inner leaf (usually brickwork or concrete blockwork)

The construction reduces the risk of water penetration through the outer walls and enhances a wall’s thermal performance.

Each leaf of the wall is connected to the other by a series of cavity wall ties, made of either stainless steel, or mild steel or iron, depending on the age of the house. Older steel or iron ties are susceptible to rusting and failure, so a programme of cavity wall tie replacement is often required, but that is a matter for another posting.

Eventually the building regulations required that cavity walls are insulated, typically with a rigid insulating ‘batt’ within the void. Older walls, usually over 40 years old, often have no insulation at all and the void is open.

Why do properties need cavity wall insulation?

For some years, adding cavity insulation has been recommended as a means of improving a building’s thermal efficiency. A system of government grants, including this most recent one in July 2020, has encouraged householders and contractors to carry out work across the country. However, not all cavity walls are suitable for insulation.

When done properly to a building in the right location there is no question that a building’s performance is enhanced. However, done badly or applied to an unsuitable property, a building’s performance can be significantly compromised.

The process seems simple, drill into the outer wall, inject a fibre or bead insulation into the cavity, make good the holes, sit back and enjoy reduced energy bills, however…

Problems that may occur include:

Water penetration
Condensation
Dampness
Cavity wall tie deterioration

Can all houses have cavity wall insulation?

There are many factors to consider when establishing suitability for cavity wall insulation. These include the construction of the wall and site conditions such as exposure to driving rain and the properties location.

This makes sense – after all, a property on top of a cliff in the north of Scotland will behave very differently to one in the centre of London.

Unless a property is fully protected you simply cannot guess the degree of exposure and this needs properly calculating.

Other aspects that must be assessed include:

Presence of cavity bridges
Width of the cavity
Condition of the brickwork
Presence of services within the wall
Existing ventilation

Walls not suitable for insulation may include:

Walls that may not be suitable for insulation include:

Walls particularly exposed to driving rain
Walls with a cavity of less than 40mm
Timber frame walls (these often have a brick outer leaf and look like cavity walls)
Metal framed buildings and walls
Walls with lots of cavity bridges
Walls in poor structural condition
Walls with a parapet that does not have a cavity tray
Walls more than 12m high (see our guide on how to measure building height)

This is not an exhaustive list and you should always seek advice if you are unsure.

What problems can cavity wall insulation cause?

We have inspected several properties where expensive cavity wall insulation has led to expensive remedial work. These are buildings where cavity wall insulation should never have been installed in the first place.

Common cavity wall insulation problems include:

Attempts to cavity insulate a solid brick wall (this may sound ridiculous, but we have witnessed it)
Poorly filled cavities causing cold spots and internal condensation
Blocked bathroom and bedroom ventilation bricks causing condensation
Blocked air bricks forming part of a gas heating ventilation system – which is dangerous
Internal dampness caused by insulation bridging the cavity and allowing moisture to penetrate
Insulation installed on excessively exposed walls such as cliff top or seaward-facing properties (something many of my readers from the Kent coast should be aware of)

Are there rules for cavity wall insulation?

The installation of retro fit cavity wall insulation is covered by the Building Regulations and must be carried out and designed by a person in a competent installer scheme.

The guidance is based on the withdrawn British Standard BS 8208 – Assessment of suitability of external cavity walls for filling with thermal insulants. This suggests a series of checks that an installer must follow to establish whether a wall is suitable for insulation. This must be done before work starts.

Before cavity wall installation begins, installers should carry out checks such as:

Assessing exposure to wind-driven rain
Measuring cavity width
Inspecting the condition of the wall
Checking ventilation openings and services
Identifying potential cavity bridges

They are common sense logical checks. If they have not been carried out, or not carried out properly then an installer has been negligent in progressing their work.

A tick box form is not sufficient as it is usually necessary to actually calculate the exposure a building has.

How do you fix cavity wall insulation problems?

As far as remedial actions are concerned, none are especially straightforward. In some cases, the best course of action is the removal of the insulation.

This may require:

Removing sections of the outer leaf of brickwork (and subsequently rebuilding)
Rebuilding parts of the wall after removal
Installing external sealants or cladding in certain situations

Each situation must be assessed individually. There may also be internal decorative repairs and damp remediation work required.

Who pays for remedial work to bad cavity wall insulation?

Well, possibly you.

Many installations are covered by a Cavity Insulation Guarantee Agency (CIGA) guarantee – often sold as being Government-backed. It isn’t.

CIGA is an independent provider of guarantees for work undertaken by its registered installers only.

How can I identify cavity wall insulation problems?

If you have internal dampness that you think is due to cavity wall insulation, or if you need to make a claim, you may want or need an independent building survey and inspection.

Common warning signs of cavity wall insulation issues include:

Internal damp patches on external walls
Cold spots or uneven wall temperatures
Condensation forming on walls
Mould growth in certain areas
Increased moisture after insulation installation

Collier Stevens can inspect cavity wall insulations and verify their compliance or otherwise with the relevant Standards and Codes of Practice. This includes the all-important calculation of exposure to wind-driven rain. This is the bit that installers very often trip up on!

And if you are an installer who is dealing with an unjustified claim, well, we have helped defend you too. Not all installations are bad.

If you think we can help you with a dispute, please contact us via the form below.

About the Author

Steven Way

Steven Way BSc MIHEEM MFPWS MRICS is the Practice Principal and is a Chartered Building Surveyor. With over 35 years as a practicing surveyor, Steve has a wealth of experience and expertise in both residential and commercial building surveying, party wall advice and disabled access auditing. He has also built his reputation as an expert witness.