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Published on March 9th, 2023

Cavity wall insulation removal: How we fix jobs gone wrong

Cavity Wall Insulation has been mandatory since 1990, but as a fairly quick job for installers it hasn't always been done well. Here's how to spot if it isn't working, and how experts like Furbnow can help.

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If your house was built post-1990 you’ll definitely have cavity wall insulation (CWI) to help keep the house warm and the energy in. Although cavity walls themselves became a thing in the late 1800’s, and prominent from the 1920’s onwards, cavity wall insulation only properly came into being in 1970 and became mandatory in the 1990’s.

If you’re not sure whether your house has it or not - have a look at the brick pattern on the exterior wall. A cavity wall has a regular brick pattern (all the bricks will be lengthwise). An older wall will be a mismatched pattern. (some of the bricks will be endways out).

The best way to see what's working and what isn't in your home is to book a home assessment and one of our accredited surveyors who'll give you a full report on your home's energy efficiency and a plan to make the changes you need. You can book a home assessment here.

1. What is Cavity Wall insulation?

Cavity Wall insulation is a layer of insulation material inserted between an exterior and interior wall to help keep the house warm by preventing heat loss. 

It exists in houses built post-1990 as a more effective way of keeping heat in - compared to previous buildings which were built with a thicker exterior wall to help keep it warm

The insulation material is usually mineral wool (the stuff you’ll find in your attic) but it can also be made up of beads and granules, or foam.

It’s installed by drilling a small hole in your wall and then blowing it in.

Cavity Wall Insulation isn’t suitable for properties in especially rainy areas as the chances of it getting wet are hugely increased.

2. How long is Cavity Wall Insulation effective?

The lifespan of the cavity wall insulation should be effective for a minimum of 25 years. There are 4 main guarantee providers in the UK, the most common of which is the Cavity Insulation Guarantee (CIGA) which came into being in 1995.

While the insulation itself, and the installation of it, are guaranteed by CIGA or the one of the other 3 providers - this can be affected by external factors which may cause issues.

3. What are potential problems with Cavity Wall Insulation?

There are several considerations with cavity wall insulation that will mean it starts to fail. If this happens it can cause other structural issues, offer reduced effectiveness and increased heating bills.

1. Damp

The insulation material needs to remain dry to retain its effectiveness. If it gets wet then it will act as a conduit for water. As well as losing its ability to retain heat, water will pass through and start creating damp and mould within the house itself.

This can happen if the exterior wall gets damaged and wet gets in via a gap in the brickwork or loose rendering. It can also happen if CWI is the only insulation change made to a house (i.e. not doing double-glazing as well) as the thermal difference between the warmer walls and uninsulated areas can be increased.

2. Ventilation

Effective insulation requires ventilation to help airflow throughout the house and compensate for the reduced airflow. If the wall has had blown insulation put in without due care then it has the potential to either block existing ventilation or cause a problem with water build up.

If you’re having cavity wall insulation put in as part of a retrofit project, the installers have a duty to ensure that they put appropriate ventilation in when required. This can take the form of window trickle vent or in the wall itself. Without this, there is an increased chance for condensation, and in turn damp.

3. Reduced effectiveness

If the insulation has been badly installed, either because it's too full or there isn’t enough material, then the insulation’s effectiveness will be reduced. 

If there’s too much then there is the risk of blocked ventilation or the insulation gets wet and leads to damp problems. 

If there’s too little, then the overall effectiveness is reduced as cold air will still make it across the gap. This can happen if the material used is too thin, or if it gets caught on an interior pipe during installation and isn’t picked up.

4. Urea Formaldehyde

In the 1970’s and 1980’s, Urea Formaldehyde was used as insulation material. Over time, it breaks down and as well as reducing the area insulated, it releases carcinogenic gases. This needs to be removed and replaced with more modern insulation.

3. How do I know if my Cavity Wall Insulation has failed?

With damp, you’ll start to notice the tell-tale signs on the wall. Internally, plaster or wallpaper will start to show signs of wetness, or a black area of mould will become evident.  

At this point, you should check the external wall and look for cracks in the brickwork, faulty guttering or other obvious entry points for water.

If the ventilation is faulty, you’ll notice both cold spots in areas where it’s lacking, or your utility bills will start to rise as the heating is working harder to keep it warm.

If your house was built in the 1970’s or 80’s you’ll need to get an assessor to come and review your walls. They’ll be able to tell you 

4. What can I do if my Cavity Wall Insulation has failed?

Luckily there are several ways of fixing issues, once they’ve been discovered. You will need to speak to an expert to come and fix it,

If you’ve noticed damp has started spreading the first thing to do is locate where the water is coming in. This could be from something like faulty brickwork, or an improperly sealed cavity. 

The goal will be to fix this leak and prevent any further water entering the insulation. If the leak is bad, or has been going on for a long time, the insulation may need to be removed and redone.

If you notice cold spots, the expert will come and assess where the insulation is missing, or whether it’s become damp.

5. Can cavity wall insulation be redone?

Yes. If the existing insulation is compromised or needs a top up, it is possible to redo.

You will need to hire a retro-fit assessor to come and review all the existing cavity wall insulation and check it’s fit for purpose, and that the house is properly insulated.

Once any existing problems are fixed (such as ageing pointing, or sodden brickwork) the insulation can be replaced.

Removing cavity wall insulation depends on the existing material. For loose insulation, a hole is drilled and a vacuum is inserted to remove the existing material.

For hard-set material, the wall will need to be partially removed so the material can be broken down and taken out - before the wall is replaced

Our roster of PAS2035 qualified retrofit teams have years of experience in assessing and fixing cavity wall insulation gone-wrong.

We’re also experts in reviewing and providing an overall strategy to effectively retrofit your home.

Written by

Robin Lewis