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Cavity Wall Insulation

Insulating your home helps to keep it warmer and will help you save energy. With the cost of energy continuing to increase it is becoming more expensive to heat our homes. Installing good insulation can save a considerable amount of money on heating bills.

If your house was built during the last ten years, the good news is that you probably already have walls that have insulation fitted into the cavity.

You will save money on your heating bills by Insulating the Cavity Walls of your home.

Insulated Cavity Walls keep you warmer and reduce your heating bills.

If the property was built prior to the 1920’s you probably have solid walls; but if it was built anywhere in-between, there is a good chance that the wall is made up of two separate walls, constructed with a space in the middle.

This type of wall will benefit from cavity insulation, and installing it could save you over £100 per year on energy bills.


What is Cavity Wall Insulation?

Over the last century most houses have been constructed with that type of external wall. The gap, or cavity, in-between can be filled with insulating materials to make the house more energy efficient. The insulation can be installed during the building of a house, as it is with most new homes, or can be retro-fitted into an existing property.

For insulation to be installed, the external walls must have unfilled cavities which should be 50mm or more deep. The brickwork of the house should be in good order to allow the work to be completed. Any walls which are exposed to heavy or driving rain may not be suitable for wall insulation.

To check if your walls have cavities you can inspect the pattern of the brickwork on exterior walls. If you can see a uniform pattern of bricks with the longest side on show, then you are likely to have a property with cavity walls.

A non-uniform pattern of bricks with a mixture of the long and short sides exposed indicates a more solid wall. A series of holes which are filled with cement along the length of a wall would suggest that the cavity has already been filled.

If you are unable to confirm whether your walls are cavity walls or if they have been filled already, you can ask a professional installer to carry out a boroscope inspection. This involves drilling a small hole in an outside wall to check if it is hollow or if it has been filled previously.


How is it Installed?

Cavity insulation should only be fitted by a professional installer and you should look for a company, which is registered to the NIA (National Insulation Association), the CIGA (Cavity Insulation Guarantee Agency), or the BBA (British Board of Agreement).

The fitter will drill a series of small holes approximately 22m in diameter along the length of the wall about a metre apart. Specifically designed equipment is then used to blow insulation through the holes and fill the cavity of the wall. Each hole is filled and sealed with cement.

If you use a professional installer and there is good access to each wall, it is a job which can be completed in a whole house within a couple of hours.

The walls must be easily accessible for the installer to ensure the fitting can be carried out quickly and safely. If the wall is adjoined to a neighbouring property, the installer will need to fit a cavity barrier to make sure the insulation is well contained and does not affect you neighbour’s wall.If there is any sign of damp in the walls this should be dealt with before any further work takes place. Walls should not have cavity insulation installed until damp problems are treated and you should contact a damp specialist before installing any insulation.


What Cavity Wall Insulation Materials Are Used?

The insulation used to fill cavities in walls is usually made up of one of three different materials; Mineral wool insulation, beaded or granulated insulation, or foam insulation.

Each of the cavity wall insulation types is subject to British standards for insulation materials and is manufactured accordingly. Any foam insulation used should carry the approval of the BBA; it should also be fitted according to the installation guidelines in the BBA certification.


Cavity Wall Insulation Cost

Indicative figures published by the Energy Saving Trust estimates that the cost of having cavity wall insulation installed would be approximately £100-£350, while the UK government estimates the cost at £50-£300 depending on the size of the property.

The effect of the insulation is estimated by both to be worth a saving of £110-£135 per year on heating and energy bills. The insulation should have a payback period of three years or less, and can save around 550g of CO2 per year.


Finding an Installer

It is important to find a professional installer who is registered to one or all of the three industry organisations listed above. The NIA offer a code of professional best practice, and you should check if your installer is signed up to this.

The CIGA offer a 25 year guarantee on approved installations carried out by their members, so you should also check that your installer is a member of the agency, and will register your installation for the guarantee.



The rising cost of electricity and gas is prompting many of us to look for practical ways of saving energy and saving money on our heating bills. Insulating a house will make it more energy efficient; it will reduce your carbon emissions, and ultimately, it will save money on the cost of energy.

Cavity wall insulation is one of the most cost-effective types of insulation for your home. The Energy Saving Trust estimates the cost of installing insulation at approximately £100-£350. As well as making your home much warmer and more comfortable, the insulation should also save you over £100 on heating bills; paying for itself very quickly.

Homes built before the 1920’s are likely to have solid walls, while any house built in the last ten years should have had cavity insulation installed during the build. If your home was constructed in the period between, it is worth finding out if you can benefit from installing cavity wall insulation.

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