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. However, 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 (www.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.
Homes less than 10 years old should already have cavity wall insulation. 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. As long as all the external walls are accessible, the job should only take a few hours, depending on the size of your house.
If there any problems with the walls, such as damp, these should be addressed first.
Cavity wall insulation typically costs £450 to £500, so it won't take too long to recoup the costs through energy savings.
Insulating homes with solid exterior walls (usually brick or stone) is much more expensive, although the savings are greater. The Trust says that fitting internal wall insulation will save you about £460 a year, or £490 if you insulate externally (based on the same three-bed, gas-heated semi). However, the work's likely to cost thousands.
Insulating internally involves fitting rigid insulation or thermal/insulated plasterboard inside the exterior wall, or creating a new, stud wall along the exterior wall and filling that with insulation.
This is usually cheaper than insulating externally, but the affected rooms will be smaller as a result. Also, you often have to remove and then reattach or replace any fittings like skirting boards, door frames and coving, so it's a lot of work and disruption, which may be fine if you're redoing the room anyway.
Although costly, external wall insulation is less disruptive because the work is done outside. Insulation's fixed to the exterior walls and covered with special cladding or render. As well as making the inside warmer and less draughty, this should improve weatherproofing, condensation levels and sound insulation, and will give the exterior walls a new look and lease of life.
In both cases, solid wall insulation is probably something you'd only consider investing in if you're planning to stay put for a long time, because while your home will be warmer, it will take many years to recoup the cost.
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