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Why get insulation?

  • Improve your home's thermal efficiency
  • Save on your energy bills
  • Slash your carbon footprint

Complete guide to cavity wall insulation

✔  Cavity walls can be filled by simply injecting insulation material into the cavity
  Homeowners can save up to £690 a year by installing cavity wall insulation
  You should be able to make back the installation cost in 2.5 years or less

Keeping our homes warm in the winter is usually our number one priority in the run-up to the chillier months. Insulation can help achieve this, but measures such a spray foam insulation cost in the thousands.

And one of the key ways that UK houses lose valuable heat is through uninsulated cavity walls. So, why not take advantage of the Green Home Grant by wrapping up your walls this winter? We’re here to guide you through the process, and answer any questions you may have.

To find out how much spray foam insulation will cost you, simply pop your details into this form and our trusted installers will get back to you.

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insulation inside a cavity wall

What’s on this page?

What is cavity wall insulation?

To understand what cavity wall insulation is and how it works, first we need to discuss the difference between a solid wall and a cavity wall. 

A cavity wall is made up of two walls with a gap in between – the outer wall is usually made of brick, the inner layer of either brick or concrete block. A solid wall, on the other hand, has no interior cavity.

Now that we’ve got that out of the way… cavity wall insulation is when a heat-retaining material is inserted into the gap between the walls, to make sure most of the warmth in your home is unable to escape.

Did You Know?

About a third of all the heat lost in an uninsulated home escapes through the walls. By properly insulating cavity walls, you will save energy and cut the cost of your heating bill.

How does it work?

In most cases, cavity walls can be filled by simply injecting insulation material into the cavity from the outside. 

The installer will drill small holes, at intervals of around 1 metre, in the outside wall of your home. They then insert insulation into the cavity using special equipment. Once all the insulation material is in, the installer will fill the holes in the brickwork so you’ll barely notice them. Simple!

Unfortunately, filling cavity walls is not a job you can do yourself, so you’ll need to get a registered installer to do this. 

Cavity wall insulation infographic

The cost of cavity wall insulation

Cavity wall insulation costs tend to vary depending on the size of your home. But whether you live in a large detached house or a small flat, you should be able to make back the installation cost in 2.5 years or less – all thanks to the savings you’ll make on your energy bills.

These savings are becoming more important as the energy crisis causes bills to rise. The Eco Experts’ National Home Energy Survey made it clear how important this is to people across the UK.

According to the survey, 60% of UK residents wanted to go greener to cut down on energy bills. Cavity wall insulation is a great way to do this.

For a semi-detached home, you can expect to pay roughly £1,000 upfront for cavity wall installation, whereas for a flat, you’ll be looking at spending around £395. 

However, you’ll need to make sure the insulation is installed correctly – otherwise, it could end up costing you more in the long run. Check out which problems to look out for on our page The Top 5 Problems with Cavity Wall Insulation.

Below, we’ve outlined how much you can expect to fork out for cavity wall insulation for each type of property.

To get a more accurate idea of how much it will cost you, simply fill in this quick form, and our suppliers will contact you with a free quote.

Spray foam insulation cost calculator

Cavity wall insulation savings

Although the initial cost of cavity wall insulation will put you back a few hundred pounds, you’re likely to make your money back in no time.

In fact, homeowners can save up to £690 a year on energy bills by installing cavity wall insulation.

Take a look at the graph below to compare how much money you can expect to save on your energy bills each year. You’ll also be pleased to see that you’ll be making a huge dent in your carbon footprint by getting your house insulated.

Cavity wall insulation grants

No matter how much we praise cavity wall insulation for its ability to reduce your energy bills, some people simply can’t justify the initial cost.

If this sounds familiar, fear not there’s still a way for you to benefit from this handy home insulation. The government has two major grants to help homeowners increase their household energy efficiency. 


Green Homes Grant 

This scheme, which ceased to exist on 31 March 2021, offered most homeowners vouchers for up to £5,000 to go towards energy-efficient home improvements such as double glazing and insulation.

The vouchers covered at least two-thirds of the costs. The lowest-income households were able to get home improvements for free, as long as they could be covered by vouchers of up to £10,000.

Unfortunately, the 1.5-year initiative was cancelled after six months, with the government missing its 600,000 homes target by a whopping 93.5%, thanks to a lack of awareness and widespread problems with the scheme.


The Energy Company Obligation (ECO) 

This government scheme means that certain energy and installation suppliers are required to support low-income, fuel-poor, and vulnerable households in heating their homes. Whether it’s to insulate your walls, or replace your boiler with a new sparkly eco-friendly one, the ECO scheme will lend a hand. 

However, not all UK residents will be eligible for this scheme. To reap the benefits of ECO, you must be a core group customer from scheme year 9 onwards under the Warm Home Discount Scheme, or you must receive at least one of the following benefits:

  • Armed Forces Independence Payment
  • Attendance Allowance
  • Carer’s Allowance
  • Child Benefit (on the condition that the household’s relevant income does not exceed the amount set out in Chapter 3 of government scheme guidance)
  • Constant Attendance Allowance
  • Disability Living Allowance
  • Pension Guarantee Credit
  • Income-related Employment and Support Allowance (ESA)
  • Income-based Jobseeker’s Allowance (JSA)
  • Income Support
  • Industrial Injuries Disablement Benefit
  • Mobility Supplement
  • Personal Independence Payment
  • Severe Disablement Allowance
  • Tax Credits (Child Tax Credits and Working Tax Credits)
  • Universal Credit

Types of cavity wall insulation

There are three main types of cavity wall insulation:

  1. Blown mineral fibre – This option tends to be the most environmentally friendly insulation to go with. Fibreglass flakes have little impact on the environment, and the raw materials used in the production of glass wool can be sourced from recycled glass, sand, and other minerals. Better still, the insulation can also be recycled once you need it replaced. Fibreglass insulates very well, and, as a result, households will use much less energy.
  2. PUR (polyurethane foam) – PUR tends to be the most effective material for cavity wall insulation, but is also the most expensive. This fluid-like material is injected into the cavity,  before expanding and filling all the gaps inside the cavity. As a result, you get seamless insulation without thermal bridges. 
  3. Polystyrene beads or granules – Similar to mineral fibre, these beads/granules are blown into the cavity using compressed air. They may be supplied loose, or in a light sticky resin to hold them together. This type of insulation tends to be cheaper than others, but beware it isn’t as efficient as PUR, and isn’t as environmentally friendly as wool. 

Compare different types of materials on our page: The 5 Best Cavity Wall Insulation Options for Your Home.

wool insulation in cavity wall

Problems with cavity wall insulation

If cavity wall insulation is installed incorrectly, it can allow water to seep into the walls. This causes structural problems and damp patches, which might also manifest into mould. 

This issue with cavity wall insulation can often take a few years to fully come to light, but we recommend keeping an eye out for the following signs, which indicate incorrectly installed insulation:

  • No noticeable increase in heat or temperature
  • Mould
  • Condensation
  • Damp
  • Damaged brickwork

What type of wall do I have?

One of the main ways you can tell if you have a cavity wall is by the age of the building. If your house was built after the 1920s, it’s likely to have cavity walls. 

Another telltale sign of a cavity wall is the brickwork on the house. You will usually find an even pattern on a cavity wall, with all the bricks laid lengthways, whereas a solid wall will have an alternating pattern, with some bricks laid across the wall (so you can see the smaller ends from the outside).

If the brickwork has been covered, you can also tell by measuring the width of the wall. Examine a window or door on one of your external walls – if a brick wall is more than 260mm thick, then it probably has a cavity. 

Next step

Once you’ve figured out all the nitty gritty details of cavity wall insulation, you’ll be well on your way to a more efficient and eco-friendly home. 

Next, all you have to do is find an installer. We recommend that you take your time to look around for the best deals – and always make sure the installer is registered with one of the following organisations:

Your home will be nice and cosy in no time! To receive a free quote for spray foam insulation, simply pop your details into this quick form

Written by:
Beth has been writing about green tech, the environment, and climate change for over three years now – with her work being featured in publications such as The BBC, Forbes, The Express, Greenpeace, and in multiple academic journals. Whether you're after a new set of solar panels, energy-saving tips, or advice on how to reduce your carbon footprint, she's got you covered.
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