Heat follows a basic principle: It moves from warm to cold areas, kind of like a heat-seeking missile. On a cold winter day, the heat from inside a house or building will inevitably escape into the colder world outside. Conversely, on a hot summer day, the heat from outside will seep into the nice, air-conditioned cavity of the house.
Estimates say that a non-insulated home loses about a third of its heat through its walls. Older houses often lack insulation. Those built before 1960 rarely have it. Those built between 1960 and 1970 may have insulation, but it may not be very good quality.
Your home may either have solid walls typically made of stone or brick or a wall with a gap or cavity behind it. In homes with cavity walls, there is an inner wall, a gap, and then an outer wall (perhaps made of brick).
Cavity Wall Insulation
Most houses build after 1920 have external cavity walls (two layers with a cavity or gap in between). Cavity insulation is used to fill the gap in order to store the heat within the inner walls, bouncing the heat back into the rooms and keeping it there longer. Cavity wall insulation gives the house a more even temperature and prevents drafts from permeating the walls.
To retro-fit an older home with insulation, an installer can inject the insulating material through the holes drilled in the external wall, particularly through the mortar joint, and fill the gap or cavity with insulation. To be effective, every part of the wall gap should be filled with insulation. If a house that requires cavity insulation is joined to another structure, a cavity barrier needs to be installed to prevent the insulation from affecting the neighbor.
The insulation installer needs to drill small holes, approximately 22mm in size, around the external wall of the house. Using special equipment, the installer blows the insulation material into the wall cavity. After filling in the wall cavity, the installer patches up the holes in the external wall.
Insulating the cavity walls in a house is never a do-it-yourself job. Instead, you should hire a registered or licensed insulation installer. The equipment can pack in the insulation with great speed and force, so the job usually goes quite quickly. The initial investment may seem large, but it can pay dividends in lower power bills down the line.