External wall insulation technical information

Heat will always flow from a warm area to a cold one, and in winter, when it is even colder outside, the heat will escape from your home into the surrounding air even quicker.

External wall insulation can significantly slow down the rate at which heat escapes, keeping as much of it inside your home as possible.

External wall insulation works by adding layers of material that only allow heat to pass through it very slowly. This reduces what is known as the ‘U value’ of the walls – the rate at which heat can flow through them. The lower the U value, the more slowly heat is lost – and the less money you will need to spend on fuel bills to keep your home warm.


Achievable U value


9″ solid wall with 70mm external wall insulation 0.24
9″ solid wall with 60mm external wall insulation 0.27
Maximum U value of new build walls permitted 0.27
11” insulated brick block cavity 0.60
0.75 inch plywood 1.08
9″ uninsulated solid wall (typically built before the 1930s) 2.10
0.5 inch of hardboard 2.94
Single pane of glass 5.60