This is a method for the determination of the overall airtightness of building envelopes. It is not a method for determining the actual air leakage which occurs through a building envelope under the natural influences of wind and buoyancy pressures, or This method is applicable to buildings with air handling systems. The testing and evaluation of a product against this standard may require the use of materials and/or equipment that could be hazardous. This document does not purport to address all the safety aspects associated with its use.