Did you know that around a third of all the heat lost in an un-insulated home is through the walls? Insulating reduces heat loss and can save you 50% on your fuel bills. If your home was built from 1920 onwards, the chances are that its external walls are made of two layers with a small gap or 'cavity' between them. This means they are 'cavity walls'. Insulating your cavity walls means filling that gap - with very good reason.
How does Insulation Work?
Heat will always flow from a warm area to a cold one. In winter, the colder it is outside, the faster heat from your home will escape into the surrounding air.
Insulation slows down the rate at which it escapes, keeping as much of it as possible inside your home for as long as possible. How? Insulation makes it much more difficult for heat to pass through your walls by filling up the cavity with a material with lots of air pockets in it. These pockets greatly reduce what is known as your walls' U value - which is a measure of how quickly they lose heat - from around 1.5 to 0.5 W/m2K The lower the U value, the slower heat is lost - and the less energy you need to keep your home warm.
You may on occasions also see references to an R-value. This is a measure of thermal resistance and is the inverse of a U-value - the higher a U-value is the lower the R-value is.