Ventilation of internal habitable rooms through another habitable room

A habitable room not containing openable windows may be ventilated through another habitable room (see Diagram 2.3) where – (a) there is, from the habitable rooms to outside, provision for both – (i) rapid ventilation through one or more ventilation openings, with a total area given in Appendix B based on at least the combined floor area of the habitable rooms; and (ii) background ventilation, of at least 8000 mm2 equivalent area; and (b) there is an area of permanent opening between the two rooms given in Diagram 2.3 based on at least the combined floor area of the habitable rooms.