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    5 tips for insulating cavity walls

    1. According to the Energy Saving Trust (, approximately one third of the heat lost in an uninsulated home escapes through the walls. This is why insulating external walls is important, especially with winter on the horizon. If your home was constructed in the last decade or so, it should have been built with external wall insulation, but most of us live in older properties, some of which have cavity walls and some don’t.


    2. Cavity walls are exterior walls with a gap in the middle that can be filled with insulation. As a general rule, houses built after 1920 have cavity walls and those built before don’t, but there are exceptions to the rule. Look at the exterior brickwork to be sure – if the bricks are all long ones, then the walls have a cavity in the middle. However, if the bricks are a mix of long and short ones, there’s no cavity because the short bricks go through the wall.

    3. Even if your home has cavity walls, cavity wall insulation isn’t necessarily recommended. The cavity should be at least 5cm across, and the exterior walls must be in good condition. Walls exposed to driving rain are not suitable for cavity wall insulation – having it installed in an unsuitable location can cause major problems, so it’s vital to first get advice from a reputable installer.

    4. Installing cavity wall insulation isn’t a DIY job – use an installer belonging to the National Insulation Association (, the Cavity Insulation Guarantee Agency (, or the British Board of Agrement ( The installer will make small holes in the exterior of the outside walls, blow insulation material, such as foam or beads, into them and then fill the holes. They’ll need to access all the outside walls and if any of the walls adjoin a neighbour’s walls, they should fit a barrier to contain the insulation.


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