What are the topsoil removal and backfill rules for building in Ontario?
Topsoil, vegetation and organic matter must be stripped beneath the building footprint before construction. Backfill against foundations must be free of debris, large boulders and frozen chunks, and graded so water drains away from the building.
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Organic soil decomposes and compresses, so slabs or footings placed on buried topsoil settle and crack years later; strip to competent native soil and have the footing bearing surface inspected before pouring. When backfilling, protect the dampproofing and drainage layer, avoid dumping heavy boulder-laden fill against a green (recently poured) wall, and brace tall walls or backfill after the floor framing is on. Final grading should fall away from the house; reverse slope is a leading cause of wet basements and warranty claims.
Before building, the dark organic topsoil must be scraped away because it slowly compresses and lets buildings settle. When the hole is refilled, the fill must be clean, gentle on the foundation, and sloped so rain runs away from the house.
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This page is provided for general information. Building code requirements depend on your specific project, occupancy and municipality, and code editions change. Always verify requirements against the current Ontario Building Code and confirm with your local building department.