What is the minimum beam size for a 10-foot cantilever on a Calgary deck under the Alberta code?

A 10-foot cantilever is an extremely long span that requires engineered design and likely a much larger beam than standard residential construction — you'll need a structural engineer to determine the proper beam size for this application.

The Alberta Building Code doesn't specify exact beam sizes for cantilevers of this length because they fall outside typical residential construction parameters. Standard residential deck construction typically limits cantilevers to 2-4 feet maximum, and a 10-foot cantilever represents a significant structural challenge that goes well beyond prescriptive code requirements.

For context, a typical residential deck beam supporting standard joist spans might be a double 2x10 or 2x12, but a 10-foot cantilever would likely require either an engineered lumber beam (LVL, PSL, or glulam), a steel beam, or a much larger dimensional lumber beam — potentially triple 2x12s or larger, depending on the loads. The beam size depends on several critical factors: the total load being supported (deck live load plus dead load), the spacing between beams, the species and grade of lumber, and the connection details at the fulcrum point.

Calgary's climate adds additional considerations for long cantilevers. Heavy snow loads from Calgary's average 128 centimetres of annual snowfall create significant stress on cantilever structures. Wet snow from chinook melt-refreeze cycles can weigh up to 480 kilograms per cubic metre, and a 10-foot cantilever supporting this load requires substantial structural capacity. The extreme freeze-thaw cycling from chinook winds also stresses every connection point, making proper fastening and flashing even more critical on long cantilevers.

This project requires professional engineering and a building permit from the City of Calgary. Any cantilever of this length will need stamped structural drawings showing beam specifications, connection details, and load calculations. The Safety Codes Officer will require these engineered drawings before issuing a permit, and the structure will need multiple inspections during construction.

When to hire a pro: A 10-foot cantilever is absolutely a professional construction project requiring both a structural engineer for design and an experienced deck contractor for construction. The engineering alone typically costs $800-2,000, and the specialized beams and connections will add significantly to material costs. This is not a DIY project or a job for a general handyman.

Find contractors experienced with engineered deck structures through the Calgary Construction Network directory — look specifically for builders who mention structural or engineered deck experience in their profiles.