The Ontario Building Code | Removal of Topsoil and Organic Matter
188.8.131.52. Removal of Topsoil and Organic Matter
(2) In localities where termite infestation is known to be a problem, all stumps, roots and other wood debris shall be removed from the soilto a depth of not less than 300 mm in unexcavated areas under a building.
(3) The bottom of every excavation shall be free of all organic material.