BSRIA S10/98 Airtightness Specifications (S10/1998) States that unnecessary air leakage of buildings leads to occupant discomfort and higher energy consumption. A key factor in providing energy efficient, comfortable buildings is specification of an acceptable rate of air leakage and subsequent air tightness testing to ensure compliance. Points out that the air leakage of standard UK buildings is generally poor, leaving considerable scope for improvement. On the basis of extensive BSRIA whole building pressurisation tests, presents the maximum air leakage rates that should be specified for buildings and enclosures, under the headings Offices - naturally ventilated and air conditioned/low energy, Factories/warehouses, Superstores, Museums and archival stores, Cold stores, Dwellings. Defines relevant terminology, discusses performance specifications, describes the test procedure and explains the data processing technique applied.