Solid wall insulation
A house built before 1920 is likely to have a solid wall with no cavity. Houses with solid brick walls are likely to have the English Bond pattern on exposed brickwork. Since solid walls lose more heat than cavity walls, insulation of a solid wall could significantly reduce your heating costs. The insulation could be fitted externally or internally.
External Wall insulation
Insulation boards are fixed to the exterior walls. These are covered with a base-layer of render which includes a mesh film for added strength and a finishing render which can be coloured and textured as wanted. High levels of insulation can be achieved and it improves weatherproofing and sound resistance. It also may reduce condensation on internal walls. Drain pipes and other exterior fixings may need moving due to the exterior surface of the wall moving outwards. This could also be a problem if the house is in a terrace. Planning permission may be required for External Wall insulation.
Internal Wall insulation
With internal wall insulation, insulation board or mineral wool is fitted against the internal surface of exterior walls and covered with plasterboard. Insulating internally reduces the floor area of a room and is disruptive, requiring rooms to be cleared and redecorated. It is however cheaper than external wall insulation, can be done room by room and avoids covering up decorative external wall brickwork.