(1) Backfill within 600 mm of the foundation shall be free of deleterious debris and boulders larger than 250 mm diam.
(2) Except as permitted in Sentence (3), backfill shall not contain pyritic material or material that is susceptible to ice lensing in concentrations that will damage the building to a degree that would adversely affect its stability or the performance of assemblies separating dissimilar environments.
(3) Backfill with material of any concentration that is susceptible to ice lensing is permitted where foundation walls are cast-in-place concrete, concrete block insulated on the exterior or concrete block protected from the backfill by a material that serves as a slip plane.