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Last updated: 14 July 2021
Correctly insulating your house can be a great first step to reducing your energy bill. Most houses built after 1920 have cavity walls, constructed with two layers of bricks with a ‘cavity’ between them. Depending on the type of build you have, cavity walls are responsible for around a third of the heat lost from your home. This is greater than the energy loss from the roof and windows. Insulating the cavity between the walls means more heat stays in the house and less fuel needed to keep your house cosy.
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Do I need cavity insulation?
Before looking to get home insulation installed, it's important to first check what kind of walls you have and whether you need insulation.
Do you have a cavity wall?
Brick houses built after 1920 are more likely to be cavity walls with solid walls being the norm up until this point. Look at the outside of your house, cavity walls can be recognised by a repeating pattern of bricks all laid lengthways. In comparison, solid walls will have either a stone exterior or a combination of bricks laid lengthways and widthways. Cavity walls also tend to be thicker than their solid counterparts. Walls thicker than 260mm are most likely cavity walls.
Do you already have cavity wall insulation?
It is important to check if the wall has already been insulated. Houses built with cavity walls in the last 20 years should already be insulated, as required by current building regulations
If your house was built before this time, professional insulation installers registered with the National Insulation Association (NIA) will be able to survey your building and confirm if you already have insulation.
In some cases, cavity insulation can also be seen spilling out of the walls into attic space, in this case, the insulation may need to be redone.
Installing cavity wall insulation
Typical insulations used include; mineral wool, polystyrene beads or polyurethane foam. While mineral wool is the cheapest and most common, to install it, your house must fit the following criteria:
- More than 50mm of cavity space
- No damage to brickwork or masonry
- No existing damp or condensation issues with the wall
- House not at risk of flooding
- Easy access to external walls
If your house does not fit these criteria, insulation is still possible and polyurethane foam can be used in instead. Polyurethane foam is a more expensive alternative and must be installed by a registered professional.
Installing cavity insulation is NOT a DIY job and a registered professional installer must be used. Confirm your installer is registered to either the, NIA, Cavity Insulation Guarantee Agency (GIGA) or British Board of Agreement (BBA). Registered installers will be correctly insured if anything goes wrong and come with a 25-year guarantee.
The installation processes itself is relatively un-invasive and will involve drilling a series of small holes at one-meter intervals in the external wall. The holes will be used to inject the insulation then filled and blended back in with the surrounding wall.
Energy and Cost Savings
In comparison to an uninsulated house, a house with cavity wall insulation will require significantly less energy to keep it warm. That means using less fuel and a cheaper energy bill at the end of the year.
The yearly savings on your fuel bill will vary depending on where you live and the current efficiency of your house. You can expect to save anywhere from £85 to £280 per year through cavity wall insulation depending on the type of build (see table below).
The installation will also vary depending on the type of home you own; however, this cost can now be offset though the current Green Home Grant offered by the UK government. This initiative provides vouchers covering up to £5000 towards the cost of environmental home improvements. Without the grant, typical insulation investments are made back within 5 years through fuel savings.
An added benefit, increasing your home's energy efficiency will reduce your carbon footprint and go some way to increasing the value of your house.