BS 6375-1:2004 pdf free.PERFORMANCE OF WINDOWS AND DOORS - PART 1: CLASSIFICATION OF WEATHERTIGHTNESS AND GUIDANCE ON SELECTION AND SPECIFICATION. BS 6375-1 specifies the exposure categories related to test pressure levels for air permeability, watertightness and wind resistance for external windows and doors. It is applicable to all types of vertical windows and doors, and includes windows in which the...