Cavity Wall Extraction and Removal

A Look at Costs and Methods

Written by Daniel Woodley. Fact checked by Hannah Miller. Published to Prices. Updated: 3rd March 2023.

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Cavity wall insulation has been missold for years but only now are the repercussions being felt by homeowners who have paid to fill their walls with this wonder insulation.

The problem?

In most cases, walls that experience windswept rain.

Water penetrates the wall soaking the insulation that then can’t dry. In many cases, mould will form on the internal walls, destroying the plaster, paintwork, and more. The repair bill can often run into the tens of thousands.

In my opinion, cavity wall insulation is the next PPI scandal, and there’s already a campaign group raising awareness (see Cavity Insulation Victims’ Alliance).

In 2021, a government advisor admitted that up to 20% of homes with retrofitted cavity wall insulation might need to have it removed.

But how much does cavity wall insulation extraction cost, how long does it take, and what methods are used?

Also, are there any alternatives?

Removal Method (Loose Cavity Wall Insulation)

I have seen first-hand how much damage insulation can cause to a property – I’ve worked on a home where we hired a firm to remove it. I’ve also conducted extensive research into cavity wall insulation removal methods in the UK and discovered that: The most common removal method is via high-powered air driven into the cavity to push the insulation to an extraction hole, where it’s then sucked out and into giant bags for removal. This method only works on loose materials such as fibre and beads – I know it works as I’ve seen it first-hand. Here is the step-by-step process:
  1. Survey the property.
  2. Drill air entrance and extraction holes at strategic locations on the walls.
  3. Inject high-pressure air into the cavity and suck out the insulation via the holes.
  4. Inspect the cavity with a tiny camera and take photos to prove the cavity is clear.
  5. Seal the holes with a suitable material (usually concrete) and paint over to match the existing exterior.
From what I’ve seen, the process is often slow and typically takes 2-4 times as long as a standard cavity wall insulation installation project. On the property I worked on, it took the workmen two full days, although it was a detached property.
Worker removing cavity wall insulation

Cavity Wall Insulation Extraction Cost

As part of my independent research for this guide, I asked 12 cavity insulation removal companies how much they charge per square metre of wall. The estimates and quotations provided to me varied wildly, but prices were in the range of £25 – £35 per square metre of wall, depending on the overall size and complexity of the project. Below is a price table based on the sizes of typical homes in the UK:
Property Size:Approx Price inc VAT
Small terraced, front and rear walls only£1750 - £2250
Small semi with 3 walls£2500 - £3000
Large semi with 3 walls£2750 - £3250
Small detached with 4 walls£3500+
Large detached with 4+ walls£4500+

Cost to Remove Solid Insulation

Solid cavity wall insulation (such as expanding foam) is far more difficult to remove and from what I know, usually requires dismantling the exterior wall in sections. 

The materials are cut out, and the section of brickwork is rebuilt; the process is repeated until all of the material is removed from the entire wall.

This is a very labour-intensive project that will essentially require rebuilding the entire exterior wall.

None of the firms I contacted was prepared to offer a price per square metre, but from my experience in the building trade, this type of work is likely to run into the tens of thousands for an entire home, even a small one.

Alternatives and Other Options

The primary reason cavity wall insulation fails is either due to the location of the wall (in a windswept spot) or its condition (damaged, cracked etc.) or both.

If the cavity insulation is already wet, it must be removed as it will take a long time to dry, even if the exterior wall is repaired.

If the cavity wall insulation is dry, but the homeowner is concerned it could get wet and cause damp and damage at a later date, there are three options:

  • Pay for it to be removed.
  • Repair the exterior wall, so any cracks and gaps are made good.
  • Seal the exterior wall with a water-repellent brick sealer such as Stormdry to prevent water ingress.

Consider Climashield

Climashield by SmartSeal is a cream that soaks into the brickwork, sealing it from water penetration whilst still allowing the wall to breathe.

This product, while not cheap, is very effective and only requires one coat.

It also lasts for decades, and when I used it. I noticed that it didn’t change the colour of the wall.

While it won’t seal large gaps and cracks, I’ve found that it’s perfect for external walls in windswept locations at risk of water penetration.

I used this on a windswept chimney breast several years ago, and it really does work; the customer reported that the water penetration stopped and never came back.

I’ve applied this excellent preventative sealer by roller and it went on really quickly, it’s also DIY friendly – read reviews on Amazon.

Water droplets on bricks

Water won’t penetrate bricks treated with Climashield

Should You Refill The Cavity With a Different Insulation Material?

Once the cavity insulation material has been removed, the property won’t be as thermally efficient, so it will cost more to heat the property.

You have a few options:

  • Leave the cavity empty and improve the insulation elsewhere (loft insulation, double-glazing windows etc).
  • Fill the cavity with a different material (such as plastic beads which *shouldn’t* soak up water).
  • Insulate the home’s internal walls (reduces the space in each room as the internal wall is thicker).
  • Insulate the exterior of the property (expensive, widens the exterior wall, requires wall rendering).

In the property I worked on several years ago, we had the insulation removed and didn’t re-fill the cavity; we just left it empty, as it was when the house was built.

What Happens if You Don’t Remove The Insulation?

There are millions of homes with cavity wall insulation, and most are trouble-free.

While there has been widespread mis-selling, in part due to the availability of government grants, most homeowners don’t need to remove the insulation.

However, if the insulation gets wet and isn’t removed, the following can occur:

  • Wall ties that hold the inner and outer walls together can rust and fail.
  • The inner wall may show signs of damp and mould.
  • Plaster may fail.
  • Damage to timber and finishings.
  • Poor air quality and breathing problems.

I have seen this damage first-hand, and it was horrendous. Entire walls had to be replastered, it took two whole days to remove the insulation, and we had huge dehumidifiers in the property, drying it out for weeks.

Other Costs to Consider

The cavity wall insulation extraction prices on this page do not include the cost of repairing any mould damage to the internal walls, replacing any rotten timbers, carpets or interior redecorating. The extraction company I hired erected their own access towers to reach the higher parts of the walls, and they didn’t need to bring in a scaffolding firm. If your property is different, it may require scaffolding which will obviously add to the cost.

External Resources

This video shows how the insulation is removed from the wall and is worth watching.

The Skill Builder YouTube channel published this insightful video about cavity wall insulation problems.

If a guarantee protects your installation, you might be able to recover the cost of removing the insulation but based on my experience, making a claim is unlikely to succeed. CIGA is the most popular guarantee provider – visit their website here.

Get a Custom Price for Cavity Wall Insulation Removal

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Our Experience, Research and Methodology

This guide to cavity wall insulation prices was written by Daniel, who has 18 years experience in the home improvement trade and has project managed a renovation where the cavity wall insulation was removed.

In January 2023, Daniel sourced prices from 12 cavity wall insulation removal companies in the UK and calculated an average cost per square metre.

The price examples shown on this page are based on the average size of typical properties in the UK.

The information regarding methods, alternatives, timescales and options is based on his experience and data from the 12 firms he contacted.

Author: Daniel Woodley

Daniel has over 18 years of experience in the construction, home improvement, and landscape garden industries, including a spell working as a project manager.

In his spare time, Daniel enjoys gardening, hiking and scrambling. He frequently posts videos to his popular YouTube Channel and is well known in the hiking community.

More About Daniel Woodley.

Daniel Woodley

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