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Cavity Wall Insulation

Cavity Wall Insulation (CWI)

Cavity Wall Insulation is always the first type of measure to consider when trying to cut your energy costs or carbon emissions. It is one of the most cost-effective measures. Installation for a typical home takes about 2-3 hours, using InstaFibre blown in white wool and all the work normally takes place outside of the home. 

Around 35% of all the heat lost in an uninsulated home escapes through the walls. By properly insulating cavity walls, you will save energy and cut costs off your heating bill.

How does cavity wall insulation work?

To insulate your cavity walls, the installer drills small holes around 22mm in size at intervals of around 1m in the outside wall of your home. The installer then blows insulation into the cavity using special equipment. Once all the insulation is in, the installer fills the holes in the brickwork so you’ll barely notice them.

How can I tell if my walls have a cavity?

There are several ways to check if your walls are solid or have a cavity:

  • The thickness of the wall. If your wall is more than 260mm thick (measure this at an outside door or window) it probably has a cavity. The cavity is likely to comprise an outer layer of brick and an inner layer of either brick or large concrete blocks

  • The brickwork. If your walls have a cavity, the outer brickwork will form an even pattern with every brick laid lengthways. If you have solid walls, some bricks in the pattern may have been laid endways.


  • The date it was built. If your home was built post-1920, it is likely to have cavity walls.

How can I tell if I already have cavity wall insulation?

Once you’ve established your walls have a cavity, how can you tell if they have already been insulated?

If the property was built after the 1990, it has probably had cavity wall insulation already built in.

If it’s an older property, check if there’s an outstanding energy performance certificate against it. These are free to access and download at the government’s official register – just search by address.
The EPC will state ‘filled cavity’ if the walls of the property have been insulated. If the walls haven’t been inspected, but the age and type of the property would suggest they should have insulation, it will say ‘assumed’.

Alternatively a survey can be carried out to commission a borescope inspection. This involves an installer drilling a small hole into your external wall using a tiny camera to see if it’s hollow or filled.

How long does cavity wall insulation last for?

It’s designed to last the life of the building, you will receive the Cavity Insulation Guarantee from CIGA which runs for 25 years.

           Download our Cavity Wall fact sheet for more information on the material we use.

To get quote for your cavity walls contact us today

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