“…In countries like the UK where most buildings are naturally ventilated, alternative approach is needed. Measurements by BRE (Perera et al, 1990 and and BSRIA (Potter et al, 1995) were obtained by attaching an external large-scale fan to the building. While the low-energy office building tested by BRE had air tightness average of those tested in North America, most conventional office buildings were found to be leakier by a few-folds.…”