The Ontario Building Code | Required Installation of Granular Fill
9.16.2.1. Required installation of Granular Fill
(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) buildingsof industrial occupancy where the nature of the process contained in the occupancy permits or requires the use of large openings in the buildingenvelope even during the winter.
In Plain Language
Granular fill beneath a floor-on-ground is required as set out in this article, providing a stable, well-drained base for the concrete slab above.
This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.