Canadian building code question

What are the building code requirements for site grading and drainage in Canada?

The building code requires site grading to direct surface water away from the building, foundation drainage systems to manage groundwater, and coordination with municipal stormwater requirements to prevent both building damage and lot-to-lot drainage issues.

Water management starts at the site before it reaches the building envelope. The code requires minimum grading slopes away from the foundation, perimeter drainage systems below the footing level, and surface drainage that does not direct water onto adjacent properties. Municipal bylaws add lot-grading requirements that must be coordinated with the building code provisions.

What to check first

  • Verify the minimum grading slope required away from the building foundation for the first 1.5 to 2 metres.
  • Check foundation drainage requirements including perimeter drains, gravel beds, and discharge connections.
  • Confirm municipal lot-grading and stormwater management requirements that apply in addition to the building code.

Jurisdiction notes

National baseline

The NBC Part 9 requires grading to slope away from the building and foundation drainage systems to prevent groundwater from reaching basement walls and floors.

Municipal lot grading

Most municipalities have lot-grading bylaws or certificates that require specific grades, swales, and drainage patterns to protect adjacent properties and the municipal stormwater system.

Provincial variation

Some provinces have additional requirements for perimeter drain material, discharge, and stormwater retention based on regional soil and climate conditions.

Work through it in this order

  1. Review the site survey for existing grades, drainage patterns, and proximity to water courses or floodplains.
  2. Design site grading to achieve the minimum slope away from the foundation as required by the code.
  3. Specify foundation drainage including perimeter drains, filter fabric, drainage gravel, and discharge to a sump, storm sewer, or daylight.
  4. Submit a lot-grading plan to the municipality if required, coordinating with the building permit application.

Common questions

What is the minimum grading slope required away from a building?

The NBC typically requires a minimum slope over the first 1.5 to 2 metres from the building. The exact gradient depends on the code edition and whether the surface is paved or landscaped.

Do I always need a foundation drain?

Foundation drains are generally required for buildings with basements or below-grade spaces. Exemptions may exist for specific soil types or where the groundwater table is consistently well below the footing level.

What if my lot grading affects my neighbour's property?

Municipal lot-grading bylaws prohibit directing surface water onto adjacent properties. A lot-grading plan or certificate may be required to demonstrate compliance before occupancy.