Throughout the late 20th century, British homes were built using cavity walls. Cavities consisted of two panels of brickwork separated by about 15 cm (6 inches) of space and were implemented to keep excess moisture out of homes. During the 1970s, builders began to experiment with installing insulation made from a variety of materials inside wall cavities to measure whether or not this could improve the energy efficiency of homes. Researchers discovered that the insulation inside the home's cavity absorbed and retained heat. Furthermore, cold air that entered from the exterior wall dissipated before spreading indoors. However, energy efficiency is not the only consideration associated with cavity wall insulation.
Cavities containing foam, polystyrene or mineral wool insulation can cause dampness inside the wall's cavity. Typically, dampness occurs when rain infiltrates the building through the exterior. Water saturates the insulation inside the wall's cavity, reducing its capacity to retain heat. The resulting dampness damages plaster, causes fungus and corrodes metal wall ties. When the moisture penetrates deeply enough, it can also ruin decor inside the home. Individuals residing in areas prone to heavy rainfall possess a higher risk of dampness in their cavity wall insulation. Alternatively, other homes risk dampness spreading inside cavities as it accumulates over the years. Homes constructed using poor construction methods or faulty materials worsen the problem.
Air pockets occur when the insulation consists of loose material, such as fibreglass wool. Rockwool can settle down near the bottom of the cavity, creating an empty space or air pocket located at the top, which often occurs when the insulation has already absorbed moisture, increasing its weight and sending it downwards. Without sufficient insulation present in all areas of the cavity, cold air infiltrates the home through the air pockets. The insulation cannot be redistributed after it settles at the bottom of the cavity, nor can the moisture be eliminated. The insulation must be removed and reinstalled.
Cavity wall insulation forms a barrier that disrupts air from flowing in or out of the home. While this barrier prevents cold air from entering the home, it also prevents air from leaving the home. This lack of ventilation can be a problem in homes containing contaminated air. Furthermore, some of the materials used to insulate cavity walls are known to release harmful toxins, such as formaldehyde, into the air. Without adequate ventilation, contaminated air is not diluted, accumulating indoors and posing health risks to individuals inside the home.