Air leakage within a house extension
A building’s design and the quality of its construction will have a major effect on the
amount of air leakage. Other factors include wind against the side of the dwelling and the buoyancy effect (warm
air rises and creates a drawing effect, pulling air in through gaps in the ground floor and walls).
Cold outside air may be drawn into the home through gaps in the walls, ground floor and ceiling (infiltration),
resulting in cold draughts. In some cases, infiltration can cool the surfaces of elements in the structure, leading
Warm air leaking out through gaps in the dwelling’s envelope (exfiltration) is a major cause of heat loss and,
consequently, wasted energy.
Disadvantages of draughty dwellings
• CO2 emissions
– A leaky dwelling will result in higher emissions.
• Space heating
– The additional heat loss will mean that a correctly sized heating system may not be able to meet the demand
– Draughts and localised cold spots can cause discomfort. In extreme cases, excessive infiltration may make
rooms uncomfortably cold during cooler periods. Leaky dwellings may also give rise to complaints from
• Risk of deterioration
– Excessive air leakage can allow damp air to penetrate the building fabric, degrading the structure and
reducing the effectiveness of the insulation.
– Air leakage paths often lead to dust marks on carpets and wall coverings that look unsightly.