Insulating your solid walls could cut your heating costs considerably, and make your home more comfortable.
If your home was built before the 1920s, its external walls are probably solid walls rather than cavity walls. Solid walls have no gap, so they can’t be filled with cavity wall insulation. Cavity walls are made of two layers with a small gap or ‘cavity’ between them.
Solid walls can be insulated though – either from the inside or the outside. This will cost more than insulating a standard cavity wall, but the savings on your heating bills will be bigger too.
Work out your wall type
If you have solid walls, then they’re almost certainly not insulated – but the first thing you need to find out is what sort of walls you have. If you can see the brickwork on the outside of the house, look at the pattern of the bricks as this can show how the wall has been built.
If your home has solid walls, the bricks will have an alternating pattern, with some bricks laid across the wall so you can see the smaller ends from the outside.

If your home has cavity walls, the bricks will usually have an even pattern with all the bricks laid lengthways.

If the brickwork has been covered, you can also tell by measuring the width of the wall. Examine a window or door on one of your external walls. If a brick wall is more than 260mm thick then it is probably a cavity wall. A narrower wall is probably a solid wall. Stone walls may be thicker still but are usually solid.
If you live in a house that has a non-traditional construction such as a concrete, steel or timber-framed building, you will need a specialist installer with experience in insulating your building type to advise you on your options.