If your home was built before 1930, 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.
Solid wall homes cost more to heat and are more prone to condensation damp than modern cavity wall built properties. When it comes to insulating your home, retro-fitting External Wall Insulation (EWI) is the most thermally efficient way of reducing heat loss in solid wall houses.