Cavity Wall Insulation

Cavity wall insulation will improve your home’s comfort and bring energy efficiency improvements that lower heat loss and heating bills.

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Keeping your home warm in the colder months can be a challenge, not to mention costly, so having a thermally efficient home is more vital than ever before. Luckily, cavity wall insulation offers a way to keep on top of costs, energy use, and temperature control with one simple solution.

Let’s dive into exactly what cavity wall insulation involves, how much it costs, and the advantages and disadvantages of this type of insulation.

Cavity wall insulation

What is Cavity Wall Insulation?

To explore this type of insulation, we first need to understand what a cavity wall is.

Some walls are solid walls, with no interior cavity. Solid walls need to be insulated by adding a layer of insulation either to the inside or the outside of the walls. A cavity wall, on the other hand, comprises two walls with a gap in between. The outer wall tends to be made out of brick, with the inner wall usually being made of brick or concrete.

  • If your house was built from the 1920s onwards, it probably has cavity walls
  • If your property is pre-1920s, it is more likely to have solid walls without a cavity

How Can You Tell If Your Property Has Cavity Walls?

If you’re unsure which type of walls your home has and if it is suitable for cavity wall insulation, there are a few easy ways to check.

If your home has cavity walls, the bricks usually have an even pattern with all the bricks laid lengthways. The bricks on solid walls tend to have an alternating pattern, with some bricks laid across the wall allowing you to see the smaller ends from the outside.

You can also tell by measuring the width of a wall. If a brick wall is more than 26cm thick, it likely has a cavity.

Why Insulate Cavity Walls?

Cavity walls perform an important function. They were originally introduced to allow air streams to blow into the hollow space between inner and outer walls and create a drying action. The cavity also allowed for the home’s masonry to drain any moisture into a safe place, so it’s great for keeping homes safe from damp.

To install wall cavity insulation, you’ll need to hire a professional to insert a heat-retaining material into the gap between the two layers of the wall. This prevents most of the heat in your home from being able to escape.

According to the Energy Saving Trust, about a third of the heat lost in an uninsulated home escapes through the walls, which underpins the importance of making sure this space in your home is adequately insulated. Most houses built from the 1990s onwards have some sort of wall insulation, possibly cavity batts which can fail over time, but homes built prior to this might not have any at all.

In some instances there may be problems with cavity wall insulation that has previously been installed incorrectly. Insufficient insulation, or uneven cavity wall insulation, can cause cold bridging or weak spots in the insulation continuity and lead to issues such as mould. Retrofit cavity wall insulation could also have been done badly previously leading to a host of cavity wall insulation problems that need remedying.

what is cavity wall insulation

How Does Cavity Wall Insulation Differ from Solid Wall Insulation?

Naturally, in a solid wall, there is no cavity to insulate. Instead, you’ll have to opt for either internal or external wall insulation, which is added to either the inside wall or the outside of your home.

Solid wall insulation is a good option for people with older properties, but there is the risk of some complications with moisture and condensation, so be sure to find a reliable installer and discuss the process with them before going ahead.

External insulation is much less invasive and doesn’t take up space in your home in the way internal insulation does, but the benefits come with a hefty price tag. If you’re on a strict budget to insulate a solid wall, internal insulation provides a cheaper alternative.

The Pros & Cons of Cavity Wall Insulation Explained

As with any type of insulation material, there are advantages and disadvantages to consider. On the whole, installing cavity wall insulation is a net positive for your property, but depending on your property’s condition, there might be a few key things to consider before going ahead with the installation.

Cavity Wall Insulation Pros

There’s nothing worse than shivering in your home during the colder months, especially if you’re worried about energy consumption and heating costs and therefore reluctant to put the heating on.

One of the biggest advantages of cavity wall insulation is that it helps to keep your house warmer throughout the seasons, meaning you don’t have to overly rely on other methods such as radiators, electric heaters, and heated blankets.

Cavity wall insulation can save hundreds on your annual heating bill, which is especially helpful when the cost of living is high. Cavity wall insulation can knock around £200-400 of your energy bills per year (depending on the type of property you live in), meaning your investment could in some instance pay for itself in around 8 years.

Every homeowner wants one thing from their home purchases – a return on investment. That’s exactly what cavity wall insulation provides.

Having cavity wall insulation installed inevitably involves a cost (the amount varies depending on the material used) but this form of insulation will tend to pay for itself multiple times over within its lifespan.

Cavity wall insulation costs are higher than some other insulation alternatives such as mineral wool insulation, but it is a highly effective insulating material. Over the decades you can improve your home’s energy efficiency to save thousands.

Not to mention that cavity wall insulation can actually increase the value of your home. Potential buyers are always looking for ways to reduce their costs, and offering a home in which insulation has already been installed is a great way to differentiate your property from others on the market.

Most of our homes are heated by burning fossil fuels, which isn’t great for the environment. If running a home that’s easy on the planet as well as your wallet is a priority, look no further than cavity wall insulation.

Having insulation reduces your dependence on using central heating to warm up your home, which in turn reduces the amount of fossil fuels you burn. If everybody in the country opted to insulate their cavity walls, our national carbon footprint would decrease significantly.

Many homeowners are put off insulating unfilled cavity walls because they fear it would be an overly disruptive process. This couldn’t be further from the truth. Installing cavity wall insulation is usually quick and straightforward when installed correctly by a professional.

With no complications, you can expect your insulation to be installed within a day – it usually takes no more than a couple of hours. Since the work is done by accessing through the outer walls, you’ll face very little disruption.

If the installation requires cavity wall insulation removal because the existing insulation has failed then this can make the installation task a little longer as the old material needs to be broken up by compressed air and then gathered up by an industrial vacuum.

Cons of cavity wall insulation

Cavities were not originally introduced as a place to store insulation. As insulation has become more popular over the years, however, the size of the cavities has increased to allow for the installation of effective cavity wall insulation.

Keep in mind that if you own an older home, the cavity may not be wide enough to fit the amount of insulation needed without causing issues. For this reason, it’s worth consulting with an expert to check that this type of insulation is suitable for your property.

Retrofitting older properties with insulation is naturally more challenging than building a new property with the insulation installed at the time, so don’t undertake this project without being sure it’s suitable.

Cavity walls aren’t there by accident; they perform a crucial role in your home’s structure, which is to keep out rain driven in by the wind. There is a small risk that if you install insulation poorly, moisture can bridge the cavity and enter your home, although this is unlikely.

Another small issue is the possibility of the wall ties (the metal rods that hold each side of the wall together) rusting when cavity wall insulation is injected. The best way to fight the possibility of damp and cavity wall insulation moisture in the home is to ensure there’s adequate ventilation elsewhere.

To avoid damp cavity wall insulation, make sure it’s installed properly by professional installers. If you notice there’s no increase in temperature and mould and condensation are showing up in your home, this indicates that the insulation was likely installed poorly. In this case, it’s best to get a professional to take a look at how to resolve the situation.

Types of Cavity Wall Insulation

There are three main types of cavity wall insulation, each with a different price point and various advantages and disadvantages.

None of the cavity wall insulation materials is suitable for DIY projects, so whichever you choose, you’ll need an experienced professional to come and install it.

Polyurethane foam insulation, or spray foam as it is commonly referred to, is known for being especially effective for cavity insulation, but its effectiveness means it is by no means the cheapest insulation material available.

The liquid-like polyurethane foam is injected into the cavity, where it expands and fills all the gaps. This makes PUR spray foam insulation perfect for entering all the nooks and crannies in your cavity, leaving you with seamless insulation.

Blown mineral fibre can often be made from recycled materials such as glass and sand, so it tends to be the most environmentally-friendly option. If you’re looking for another way to boost your eco credentials alongside reducing your reliance on fossil fuels, blown mineral fibre insulation is your best bet.

This type of insulation is made from fibreglass flakes, which can be recycled themselves once you’re finished with them. It’s installed by being blown into the cavity using compressed air. While not as effective as PUR at filling space spaces and corners, blown mineral fibre is still an excellent option.

These polystyrene beads and granules work similarly to blown mineral fibre in that they’re blown into the cavity. You’ll find these materials supplied either loose or held together in a sticky resin. They are a good option as they don’t absorb moisture.

If you’re looking at filling cavity walls but on a strict budget, polystyrene bead insulation is usually cheaper and quicker to install than the others, but it may not be as cost-effective in terms of long-term savings since it’s less efficient than PUR.

How Much Does Cavity Wall Insulation Cost?

Naturally, cavity wall insulation costs will vary depending on different factors. Insulating a large detached house will cost more than insulating a flat, and you may pay a different price depending on where you live in the country.

Prices for installation in the North will tend to be cheaper than the prices in the South East, for example.

There are two parts to the cost of cavity wall insulation – labour and materials. The price for the materials is what you pay for the type of insulation being used, while the labour is what you pay to have a professional come and install it.

Because of the specialist equipment and techniques needed to install cavity wall insulation, it’s not something you should take on as part of a DIY project, so labour costs are unfortunately unavoidable.

Make sure you’re getting bang for your buck by working with trusted professionals with a record of success. Some insulation materials, such as cavity foam insulation, are also more expensive than others, so the price will differ depending on the type of insulation you choose.

In general, you can expect to pay approximately £200 per cavity wall. Imagine you own a mid-terraced home, for example. You’ll only need to insulate the external walls (not the ones that connect to another home), so that would cost you around £400.

You can expect to pay more for a detached property, but bungalows are the cheapest type of detached property because the walls are shorter.

Cavity wall insulation is much cheaper than solid wall insulation, which tends to cost thousands of pounds.

Can I Get a Grant for My Cavity Wall Insulation?

Despite the cost-effectiveness of cavity wall insulation, its price point makes it inaccessible to millions of people around the country. The good news is, there are many grants available to those who need them, to make their homes more efficient and help reduce the costs of their energy bills.

You may be eligible to have cavity wall insulation installed for free if you receive one of the following benefits.

  • Child Tax Credit
  • Housing Benefit (not the single person’s 25% Council Tax reduction)
  • Income-Based Jobseekers Allowance
  • Income-Related Employment Support Allowance
  • Income Support
  • Pension Credit Savings Credit
  • Pension Guarantee Credit
  • Universal Credit
  • Working Tax Credit
  • Child Benefit  

How Long Does Cavity Wall Insulation Last?

If installed properly, cavity wall insulation should last in many instances for as long as you are living in the property itself – this could be many decades. The improved thermal insulation brings energy bill savings that add up over time.

This means that if you spend a few hundred getting a cavity barrier installed, you’ll make your money back multiple times over in savings by the time you come to move out of your home. In fact, most homeowners are expected to get payback on the cost of installing cavity wall insulation within 2-3 years.

Is Cavity Wall Insulation Right for Your Property?

To start with, it’s worth checking whether your cavity walls are already insulated, which is a high possibility if your home was built in the last 20 years. If your cavity walls are already insulated but you still want to improve your home’s energy performance, consider other types of insulation.

If you’re not sure either way, ask a professional installer to perform a borescope inspection to explore your wall or check with your local authority.

Cavity wall insulation isn’t suitable for every type of property. Check whether your home meets the below criteria before having cavity wall insulation installed.

  • The external walls are uninsulated cavity walls.
  • The walls are not exposed to driving rain.
  • Your house is not in a high-risk flood zone.
  • Your property’s masonry and brickwork is in excellent condition.
  • The cavity is at least 50mm wide and doesn’t contain rubble or any other foreign objects that could impede the installation of insulation.


You should then ask your installer of choice to carry out a survey to assess whether your property is suitable. If you live in a flat, you’ll need permission from the people in the surrounding flats before you go ahead with installation.

How to Find the Right Cavity Wall Insulation Installer

Naturally, it can be overwhelming to look for the right cavity wall insulation installer, but there are some easy steps you can take to find the right one.

  • Look online for installers that cover your local area – we can help you with this by introducing you to a registered installer.
  • You can ask your potential installer for any relevant qualifications, testimonials, reviews, and a quote regarding installation cost. (Accreditations such as the Cavity Insulation Guarantee Agency (CIGA), National Insulation Association (NIA) and British Urethane Foam Contractors Association are good indications of quality installers).
  • Ask any questions you have before getting started.


If you’re not sure whether your walls have wall cavities or are solid walls, or indeed if you already have cavity wall insulation, you can always ask a professional installer to check. It is usually possible to find out just by viewing the outside walls or looking for signs of drill holes or small homes made by a previous wall cavity installation. A professional installer will also be able to advise on the best form of cavity wall insulation for your home.

Whichever type of insulation you opt for, you’re sure to reap rewards with a much more energy efficient home. In most cases, you can expect your insulation cost to be covered in just a few years through reduced heat loss and energy bill savings.

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