Since the 1920s or so, most houses were built with two external walls that sandwich a cavity that lies in between, sort of like double glazing. The cavity between the walls helps improve insulation and prevents moisture intrusion, but filling it with cavity wall insulation vastly improves its thermal performance.
Some 1/3rd of heat generated in a home is lost through the walls. This makes the walls a prime target for improved insulation.
According to Which?, cavity wall insulation can shave £150 to £280 off the yearly energy bills of an average 3-bedroom semi-detached house. Considering the initial outlay, cavity wall insulation can pay for itself in under 5 years without much hassle at all.
Savings are highest for houses with more outside walls (e.g. detached houses), or houses particularly large outside walls.
In this article, we’ll cover how much you can expect to pay for cavity wall insulation and other common questions around cavity wall insulation.
Average Cavity Wall Insulation Cost
By finding quotes from 6 cavity wall insulation installers and 8 secondary sources, we discovered the following all-in average costs for cavity wall insulation.
Whilst some materials are slightly more expensive than others (e.g. PUF), the difference is pretty small overall and falls within the following average ranges.
Type of Property Installation cost
Detached house (4 bedrooms+) £1000 - £1,250
Semi-detached house (3 bedrooms) £900 - £1,150
Mid-terrace house (3 bedrooms) £600 - £800
Detached bungalow (2 bedrooms) £600 - £900
Flat (1-2 bedrooms) £600 - £900
Does My House Have Cavity Wall Insulation?
You’ll first need to check whether or not your house:
- Has cavity or solid walls
- Already has cavity wall insulation
There are quite a few ways to check:
- As mentioned, houses built after the 1920s tend to have cavity walls – walls with an empty space of air between them. Houses built after the late 1990s may also have insulation in the cavity walls already. Houses built post-2000 are strongly likely to have cavity wall insulation already.
- If you have an old house, you can check the brickwork to see if your home is doubled cavity walled or single-walled. Single-walled brickwork has an uneven pattern, as bricks are laid both horizontally and perpendicular, facing inwards, thus revealing bricks that appear shorter than others. Cavity wall houses feature a regular and even pattern of horizontally placed bricks.
- You can also check your wall for roughly 1-inch diameter holes that will have been used to fill the house with insulation These show that your wall has been cavity insulated already.
- You can also check in your attic, as the insulation may be spilling out over the tops of your walls.
- Your wall status and energy performance certificate (EPC) is also available via this government tool. Your local authority’s Building Control may also be able to tell you whether or not your building has been cavity insulated – you can phone them or email them.
- Wall insulation status may also be found on a CWI survey conducted on your home when you moved in or when a previous owner moved in. This is more likely for older houses or listed buildings.
- Finally, you can ask a cavity wall installer to conduct a survey of your home. Most will be able to tell easily by simply studying your outside walls for evidence of cavity wall insulation. They can also insert a camera via a borehole to assess if you have cavity wall insulation and how good it is.
Should I Get Cavity Wall Insulation?
Cavity wall insulation might be viewed as a bit ‘old hat’, but many houses still lack it and there are plenty of benefits.
First and foremost, cavity wall insulation yields savings on your energy bill. Below is a table of the average bill savings from cavity wall insulation.
|House Type||Energy Savings Per Year||Average Payback Period|
As we can see, cavity wall insulation pays for itself quickly. In most cases, the outlay of insulation is recuperated in 5 years or under.
Moreover, cavity wall insulation can boost your home’s EPC energy certificate that can increase the value. Even a small increase makes cavity wall insulation a worthy investment.
Another benefit of cavity wall insulation is that it soundproofs the walls of a house and can also prevent damp intrusion. Some types of cavity wall insulation are better at soundproofing than others. Polystyrene bead insulation is probably one of the best insulators for soundproofing.
It’s worth pointing out here that if you leasehold or freehold a flat then you’ll only be able to get cavity wall insulation if others with the same party wall agree also to get cavity wall insulation. This might be hard to negotiate if there are rental or council properties adjoined to the same wall.
Local councils have run their own flat cavity wall insulation programs, like this one conducted in 2013 by Haringey council. By offering subsidised rates or even free cavity wall insulation, the council administered insulation to some 499 flats.
Local schemes like this run all the time and your council may have its own incentives or schemes for those looking to improve the energy performance of their home. Do your research prior to searching for an installer.
Getting a Grant for Cavity Wall Insulation
It’s possible to receive a grant to fully or partially cover the cost of cavity wall insulation. There used to be types of grants available – the ECO grant and Green Homes Grant – but the Green Homes Grant closed in March 2021. It will be replaced with a new type of grant in the future.
Energy Company Obligations (ECO)
The first grant falls under the Energy Company Obligations (ECO) scheme. This obligates energy companies to subside some of the cost of cavity wall insulation, as well as loft insulation and boilers. It’s currently only available to those with a household income of £16,190 or less who are claiming certain benefits.
To enquire and claim on the ECO scheme, you must contact your energy supplier. Some installers can do this on your behalf. There are also local council schemes in place to expedite access to ECOs, so check with installers in your local area and ask them about the ECO scheme.
Most energy suppliers participate, including:
- Avro Energy
- British Gas
- EDF Energy
- Octopus Energy
- Scottish Power
- Shell Energy
- Utility Warehouse
Even if your energy isn’t supplied by one of these companies, you’re still entitled to the ECO if you meet certain criteria. To receive the grant, you have to contact a participating energy supplier directly.
Not everyone will receive the grant – it depends on your home and how much energy you would likely save from cavity wall insulation. See Ofgem’s website for more details and contacts.
There seems to be a lot of leeway when it comes to ECO grants and different councils have different approaches, so always check with your council, installer and energy supplier first, even if you don’t think you’re eligible.
Types of Cavity Wall Insulation
There are a few types of cavity wall insulation used today. The most common and up-to-date types of cavity wall insulation are probably insulative beads and granules and polyurethane (PU) foam.
Older types of insulation include urea-formaldehyde which has been known to degrade into harmful gasses. If you find this on a cavity wall inspection then you should consider having it removed, particularly if it has already started to degrade.
Mineral Fibre Insulation
Mineral fibre is still a very popular type of insulation and can be blown into cavities. It’s easy to fit, provides good insulation and is relatively inexpensive. It’s not particularly environmentally friendly as it’s made from molten rock bonded to synthetic fibres.
Wool fibre was traditionally made from sheep’s wool and often still is. There are synthetic alternatives available. It can also be blown into the cavity for easy insulation. It’s not particularly cheap but is quite eco-friendly.
EPS – Expanding Polystyrene Beads or Granules
One of the most common types of cavity wall insulation since the 90s, EPS granules are small balls of polystyrene that are sprayed into the cavity wall. They’re excellent insulators and are pretty cheap. Not particularly eco-friendly, though.
Polyurethane Foam (PUF)
Probably the best insulator, polyurethane foam can also fill small spaces within the wall. It’s an excellent soundproofing material as well as an insulator. It is the most expensive option and does require a PUF specialist to fit.
Average Costs of Cavity Wall Insulation
By finding quotes from 6 cavity wall insulation installers and 8 secondary sources, we discovered the following all-in average costs for cavity wall insulation. Whilst some materials are slightly more expensive than others (e.g. PUF), the difference is pretty small overall and falls within the following average ranges.
Cavity Wall Insulation Building Regulations
If possible, find an installer that is recommended by the Cavity Insulation Guarantee Agency (CIGA). A CIGA supplier will also ensure that your cavity walls are self-certified with Building Regulations – more information on the Planning Portal.
If you own a Listed Building or building in some form of conservation area then check with your Local Planning Authority before you begin work.
Choosing a Cavity Wall Insulation Contractor
It’s recommended to find a Cavity Insulation Guarantee Agency (CIGA)-registered contractor.
In the past, there have been problems with dodgy installations that eventually lead to damp intrusion, mould and other structural issues. The CIGA also provides an insurance-backed guarantee on the longevity and quality of the insulation works.
Don’t skip the borescope survey if it’s suggested to you – this might be the difference between a good and bad installation.
A portfolio of past work is essential – don’t be tempted by cold callers or installers that turn up on your doorstep.
Cavity Wall Insulation Process
Cavity wall insulation typically takes just one day. It’s not a tricky job unless there are unforeseen problems. Jobs on large detached houses with large outside walls might take 2 days.
The installer will carry out a survey of your wall, possibly using a borescope to investigate whether there is pre-existing cavity insulation and what state it’s in. The survey will also determine whether the walls are suitable for expanding PFU or another type of insulation. This won’t take long but be aware that a borescope survey, if needed, may add an extra £200 or so to the installation.
Holes of roughly 20mm or one inch are drilled at regular intervals along the wall, usually 1 metre apart. The blower clamps into the hole and squirts the material inside the wall cavity. The machine has a pressure gauge that alerts the operator when to move on. The holes are then filled with cement mortar. That’s pretty much it. It’s quite a loud process but vibrations to the home are low with modern machinery so your electrics and brickwork should be fine.
Make sure you receive a certificate of completion that also details the type of insulation received, including the exact brand and specifications. If you claim through the ECO scheme then you’ll need to submit your invoice and other proof of work to receive your money.
Get Prices on Cavity Wall Insulation Near You
We’ve done our best to give you a good idea of what you can expect to pay to install cavity wall insulation.
However, our guides are not a substitute for a fixed quote specifically for you.
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