(1) Except as provided in Sentence (2), not less than 100 mm of coarse clean granular material containing not more than 10% of material that will pass a 4 mm sieve shall be placed beneath floors-on-ground.
(2) Granular material need not be installed under,
(a) slabs in garages, carports or accessory buildings, or
(b) buildings of industrial occupancy where the nature of the process contained in the occupancy permits or requires the use of large openings in the building envelope even during the winter.