Insulating your solid walls could cut your heating costs considerably, because solid walls let through twice as much heat as cavity walls do. The good news is they can be insulated.
If your home was built before 1919, its external walls are probably solid rather than cavity walls. Cavity walls are made of two layers with a small gap or ‘cavity’ between them. Solid walls have no gap, so they let more heat through.
Another way to tell is by measuring the width of the wall. Look at an external wall window or door and if the brick wall is less than 260mm, then it is likely a single brick solid wall 260mm to 300mm a cavity wall, while if it is greater, it is probably a solid stone wall.
Solid wall insulation
Solid walls can be insulated – 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.