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Cavity Wall Insulation Explained

One of the cheapest and easiest ways to heat up your home and reduce your energy bills is to install cavity wall insulation. Here we look at what exactly it is, how much it can save you and how to get it for free.

What is cavity wall Insulation?

You may be alarmed to know that around a third of the heat in your home is lost through the walls. One of the easiest ways to rectify this is to make sure that your property is fitted with cavity wall insulation. This type of insulation will not only have the effect of reducing your carbon footprint, but could result in huge savings on your energy bill.

If your home was built before 1990, there is a chance that your walls are insulation free. This means that  you have the opportunity to add instant warmth to your home and a little less drain on your bank balance.

How is Cavity Wall Insulation fitted?

There are two main options for installing cavity walls. The first is inserting sheets of insulation material, usually semi-rigid glass mineral wool or rockwool, in the cavities as the walls go up during construction.

The second is to have it retrofitted afterwards by injecting insulating directly into the walls from the outside. A specialist installer will drill small holes at regular one metre intervals into the exterior of your property and inject the material. This material is usually either rockwool or polystyrene beads and put into the cavities before resealing with cement.

How to tell if you have cavity walls?

While standard cavity wall insulation will be a viable option for a lot of people, there are some that won’t be able to have it fitted as their property will have solid walls.  If your home was built before the 1920s, it is likely that it has solid walls.

Solid wall insulation differs in that it involves attaching a layer of insulating material to the wall, then covering it with render or cladding, before adding a finish.

The biggest clue in working out whether you have cavity or solid walls is looking at the brick pattern on the outside of your property.

Homes with solid walls have bricks with an alternating pattern, with some bricks laid vertically across the wall, so you can see the smaller ends form the outside.

Cavity walls on the other hand are usually made up of bricks that have been placed lengthways. You will notice this on the outside of most modern houses.

Solid wall: bricks are alternate in pattern.

Cavity wall: bricks are in an even pattern and laid lengthways.

Is your home suitable for cavity wall insulation?

There is a range of criteria that your home must meet in order to have standard cavity wall insulation fitted.

These are:

  • The external walls are unfilled
  • Your cavity is at least 50mm wide
  • The cavities are free of rubble
  • The masonry or brickwork of your property is in good condition
  • The walls are not exposed to driving rain
  • Your house is not at risk of flooding

For those properties that are exposed, at risk of flooding, or with narrow or uneven cavities, polyurethane foam can be injected into the cavities. While this can be a more expensive solution, it can prove to be an effective insulator.

If you have damp patches in your internal walls, these will need to be rectified by a professional builder before any insulation can be injected. If you are concerned about a damp build up in your home, you can read our guide on how to get rid of damp.

In all cases, a full survey should be carried out by a building professional before you go ahead, who will use instruments such as a borescope to inspect inside the walls.

Can you install cavity wall insulation yourself?

The simple answer is no. Installing cavity wall insulation can be a tricky undertaking, with lots of building regulations and particular circumstances to consider.

Installers should belong to either the National Insulation Association (NIA), the Cavity Insulation Guarantee Agency (CIGA) and the British Board of Agrément (BBA).

You should also check that that the installer is signed up to a code of professional practice and that the work is guaranteed for 25 years by CIGA or an independent insurance-backed guarantee.

How much does cavity wall insulation cost?

Like all insulation, the cost of cavity wall insulation differs depending on the type of property. The typical price for a detached house is £610, while it’s £475 for a semi and £390 for a mid-terraced property.

How much could cavity wall insulation save you?

he best thing about fitting this type of insulation is that you’ll quickly notice the savings on your energy bill.

Occupants of a typical detached house can expect to save £305 a year on their bills, while those in a semi can save around £475, and mid-terrace owners almost £400 annually.

How much C02 will you save with cavity wall insulation?

It’s not only money you’ll be saving with cavity wall insulation, but you’ll also be doing your bit to save the planet with hugely decreased CO2 emissions.

Figures from the Energy Saving Trust show that the average detached house can expect to reduce their CO2 output by 1150 kilograms a year by fitting the insulation. Considering that the average home emits 2.7 tonnes OF CO2 every year, that’s a massive reduction of 41.9%.

The results are similarly impressive in semi-detached properties, with a 25% CO2 saving, and a 16% saving in mid-terraced properties.

Can you get free cavity wall insulation?

There are a number of cavity wall insulation grants available that can cover either the total or partial cost of the fitting. The main ones are the Energy Company Obligation (ECO) grant, and the Green Homes Grant voucher scheme.

What are ECO Grants?

The Government’s Energy Company Obligation (ECO) is a government-backed energy efficiency scheme that obligates the UK’s big energy companies to help customers on certain benefits afford energy saving home improvements. As well as helping them secure a free boiler, the scheme also covers a range of other energy saving measures, including cavity wall insulation.


What is the Green Homes Grant Voucher Scheme?

The Green Homes Grant voucher scheme (GHGVS) provides vouchers for energy efficiency measures, including funding for cavity wall insulation.

The scheme is split between those on low incomes and certain benefits, who can apply for vouchers that cover the total cost up to £10,000. There is also  a more general scheme that is open to everybody and provides grants that cover two thirds of the cost, up to £5,000.