Mind the gap to keep warm and save cash

Thermal insulation of a brick wall.
Thermal insulation of a brick wall.
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Millions of UK homes have cavity walls – which means there’s a gap in the middle of exterior walls – and filling them with insulation can make your home more energy efficient.

This means reduced heating costs, and you’ll be making your house ‘greener’ in the process.

Finding out if your home has cavity walls isn’t hard. In general, houses built after 1920 do, and those built before don’t. But you can’t tell by the house’s age alone.

Look at the brickwork – if the bricks are all long (whole) ones, then the walls have a cavity in the middle, but if the bricks are both long and short ones, there’s no cavity because the short ones go through the wall.

According to the Energy Saving Trust (energysavingtrust.org.uk), installing cavity wall insulation in a three-bed semi (with gas central heating) will produce savings of up to £140 a year.

But the walls need to be in good condition and not exposed to driving rain, and the cavity must be at least 5cm deep.

If you’re not sure about yours, ask your local council’s building control department if they have a record of the walls being filled, or get a registered installer to drill a hole in the walls to see.

A registered installer must also fit the insulation – this is not a DIY job. They’ll do this by making small holes in the external walls, blowing insulation material into them and then filling the holes.