Windows and doors within a house extension
It is common to find gaps between the window frame and the wall. They may also occur between
the frame and the opening casements, lights and sashes. The window’s opening/closing mechanism can become loose
with time, and may not close as tightly. If this is the case, a draughtstrip may not be sufficient to seal the
In timber windows, excessive swelling and shrinking, as well as decay, may result in air leakage through the
frames and around the opening window lights.
Air leakage can also occur around the window reveals and window board
Large gaps between the bottom of an external door and the threshold are common, especially around slider
mechanisms for patio doors. Another common air leakage path is the letterbox.
Leakage into ceiling voids and the roof space
Air can leak past a poorly fitting loft hatch up into the unheated roof void. Warm moist air from the house may
then condense on cold surfaces in the unheated loft and lead to condensation problems.
Light fittings – and gaps around them – can offer a path into the roof void and also into the void between the
ceiling and the next floor. Air can leak out indirectly from this void through gaps in the external walls (such as
those around joists that penetrate the air barrier) and through unfinished mortar joints.