Wall Insulation

Approximately one third of all the heat in a property is lost through the walls of a building if there is no insulation. Heat travels from the warmest environment to the coldest environment. This means that the colder it is, the faster heat will be lost from the property.
Since the 1990’s all houses have had to be built with insulation between the two outer walls. However, if your house was built before this time, the chances are that it does not have any insulation. Insulating the space between the walls could save you approximately £140 per year.
Cavity walls and solid walls
Most houses in Britain have either solid or cavity walls. Cavity walls are where there is a space between the outer walls and solid walls are as they say, solid. Houses built before 1920 tended to be solid walled. After that time, houses were built with cavity walls.
If your house has cavity walls, the bricks will probably have a pattern similar to this:

If your home has solid walls, the bricks will have an alternating pattern like this:

If your house has been rendered and you can not see the pattern of the brickwork, then measure the thickness of the walls in the window space. If the wall is more than 26cm thick, then it is probably a cavity wall. If it is much thicker than 26cm and your house is built of stone, then it is a solid wall.