Cavity walls are made of two layers with a small gap or ‘cavity’ between them. Solid walls have no such gap, so they let more heat through. Solid walls can be insulated – either from the inside or the outside.
Heat rises, and in an uninsulated home a quarter of your heat is lost through the roof. Insulating your loft, attic or flat roof is a simple and effective way to save that waste and reduce your heating bills.