Solid / External Wall Insulation
About 35% of all heat loss from UK homes takes place through external walls. Most homes built before 1920 have solid walls.
Solid walls are usually notoriuosly bad for retaining heat, typically allowing twice as much heat to escape as cavity walls.
Solid walls can usually be insulated either by applying high density insulation material internally, externally or both.
If you're unsure whether your walls have a cavity in them you can usually check by either looking at the pattern of bricks or by measuring the thickness of the walls next to a door or window:
If the thickness of the wall is 260mm or greater, the wall probably has a cavity.
If the brickwork is exposed, look at the brick pattern. If the bricks are all oblong, laid end-to-end then the wall is likely to have a cavity. If some of the bricks are laid with the square end facing, the wall is likely to be solid.
If the wall is stone, it is likely to be solid.
The Energy Saving Trust estimates that an annual saving of £460 is achieved on an average detached house in the UK.