How does loft insulation work?

Heat will always flow from a warm area to a cold one. The colder it is outside, the faster heat from your home will escape into the surrounding air.

Insulation makes it much more difficult for heat to pass up through your roof by providing a layer of material which has lots of air pockets in it. These pockets trap heat, cutting what is known as the U value of the loft.

The U value measures how quickly it loses heat so the lower the U value, the less energy you need to keep your home warm. Loft insulation cuts your loft's U value from around 2.3 (for an un-insulated loft) to 0.16 W/m²K, a reduction of around 95%. You may on occasions also see references to an R-value. An R value is a measure of thermal resistance and is the inverse of a U value so the higher the R value the better. The NIA recommend lofts should be insulated to an R value of between 6.1 and 7 Km²/W. The R value is usually displayed on the packaging of insulation. R values can be added together to reach the total required.