Canadian building code question

What are the building code requirements for retaining walls and foundations in Canada?

The NBC requires foundations and retaining walls to be designed for applicable loads including soil pressure, frost, water, and seismic forces, with requirements for minimum depth, drainage, waterproofing, and geotechnical investigation that vary by building size and soil conditions.

Foundations and retaining walls transfer building loads to the ground and resist soil and water pressures. The National Building Code sets requirements for foundation design that ensure structural safety, frost protection, and moisture control, with provisions that range from prescriptive rules for simple residential buildings to engineered design requirements for larger or more complex structures.

What to check first

  • Foundations must extend below the frost depth for the building location, as specified in the NBC climatic data tables.
  • Retaining walls must be designed for lateral earth pressure, surcharge loads, water pressure, and seismic forces where applicable.
  • Foundation drainage and waterproofing or dampproofing are required to protect against water infiltration and soil moisture.

Jurisdiction notes

National baseline

NBC Part 4 covers structural design requirements for foundations. Part 9 provides prescriptive foundation requirements for houses and small buildings. Both reference CAN/CSA standards for structural design.

Provincial variations

Provinces may have additional foundation requirements for specific soil conditions, seismic zones, or climate regions. Frost depth data varies significantly across Canada.

Geotechnical requirements

Buildings over certain sizes or on challenging soils require a geotechnical investigation to determine bearing capacity, settlement, and lateral pressure parameters.

Work through it in this order

  1. Determine the frost depth for the building location from NBC climatic data and set the minimum foundation depth.
  2. Classify the building to determine whether prescriptive Part 9 or engineered Part 4 foundation design applies.
  3. For retaining walls, calculate lateral earth pressure, surcharge, water pressure, and seismic loads.
  4. Verify drainage requirements including foundation drains, grading, and waterproofing or dampproofing.
  5. Confirm geotechnical investigation requirements and bearing capacity for the foundation design.

Common questions

How deep do foundations need to be in Canada?

Foundations must extend below the frost depth for the building location, which ranges from under 1 m in mild coastal areas to over 2.5 m in colder regions. The specific depth is published in NBC climatic data.

When is a geotechnical investigation required?

The NBC generally requires geotechnical investigation for buildings designed under Part 4 (larger buildings). Part 9 permits prescriptive foundations on soil with adequate bearing capacity, but a geotechnical report is recommended for all but the simplest conditions.

Do retaining walls require a building permit?

Most jurisdictions require a building permit for retaining walls over a certain height (commonly 1.0 m to 1.2 m). Engineered design is typically required for walls exceeding the prescriptive limits in the code.