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How to work out which type of wall insulation is right for your home

Posted on 3 May 2016

With about a third of the heat lost in an uninsulated home escaping through the walls, investing in wall insulation can significantly reduce your energy bills. On top of that, making energy saving upgrades to your home will also shrink your carbon footprint, which is great news for those of you striving to live a greener lifestyle.

However, depending on the age of your property, wall insulation can be fairly costly. To work out which type of wall insulation is right for your home, and to make sure it’s a worthy investment, here’s a quick breakdown of what you need to know.

Wall types

In the UK, most buildings have either cavity walls or solid walls. If your home was built prior to 1919, your house is likely to have solid walls. This means your external walls are just single, solid walls usually constructed out of brick or stone. Cavity walls on the other hand consist of two walls with a gap between them, referred to as the cavity. The outer layer tends to be made of brick and the inner layer is usually either brick or concrete.

Before you get underway with your wall insulation, you need to work out what type of walls you have. The easiest way to tell is by studying the brick pattern on the outside of your house. Cavity walls tend to have a regular brick pattern showing the long sides of the bricks, whereas solid walls have an alternating brick pattern showing the long side of the brick, then the short end of the brick.

For other wall types such as pre-fabricated concrete and steel or timber framed buildings, you may need to seek specialist help to insulate your walls.

Cavity wall insulation

If your home was built post 1920, it’s likely it will have cavity walls. Houses built within the last 10-15 years are likely to already have cavity wall insulation, but you can find out for certain by either asking an installer for a boroscope inspection or by checking with your local authority’s building control department.

Cavity wall insulation works by filling the gap between the two walls. An installer will drill small 22mm holes around the outside of your home, then blow the insulation into the cavity between your walls. Once it’s filled, they’ll also fill the holes in the brickwork. Your external walls will need to be in a good condition for them to be suitable for cavity wall insulation.

Is it cost effective?

Before you go ahead with cavity wall insulation, you need to work out if it’s actually going to benefit you. The typical installation cost of cavity wall insulation will vary depending on the type of property you live in, but tends to range from around £370 for a mid-terrace house to £720 for a detached property.

However, after the cavity wall insulation is in place, you could save anywhere from £105 - £275 per year on your fuel bills for mid-terrace houses and detached houses respectively. That means cavity wall insulation tends to have a payback time of five years or less, making it a very cost effective investment if you’re planning to spend more than five years in your current home.

Solid wall insulation

If you live in an older building, your home is likely to have solid walls. Solid walls lose twice as much heat as cavity walls, so insulating them will cut your energy costs by around £175 per year for mid-terrace houses and as much as £455 per year for detached houses.

However, solid wall insulation is more expensive than cavity wall insulation. Solid walls can be insulated either internally or externally, with each having different benefits and disadvantages.

Internal wall insulation

Internal wall insulation is carried out by fitting rigid insulation boards to the inner wall, or by constructing a stud wall and filling it with insulation material. This type of insulation tends to be cheaper than external wall insulation, which can make it a more cost effective option. Internal wall insulation usually costs between £3,500 - £14,000, however this still gives it a payback time of around 20 years.

There are also other factors to be considered with internal wall insulation, such as it will slightly reduce the floor area of the insulated rooms and the installation process can be disruptive to everyday living.

External wall insulation

External wall insulation is done by fixing a layer of insulation material to the external wall, then covering it with a specific type of render or cladding. The finish can be anything from smooth to pebble dashed.

There are numerous benefits to investing in solid wall insulation, including improved weathering and sound resistance, reduced draughts, preventing damp and increasing the longevity of your walls. On top of that, the process doesn’t disrupt everyday living or reduce the floor area of your home.

However, external wall insulation can be far more expensive, usually costing around £8,000 - £22,000 to install. This means that the payback time in reduced fuel bills could be over 30 years. Although, it’s also important to factor in benefits such as increasing wall longevity, as the initial cost of external wall insulation could be cheaper than repairing future wall damage.

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