Span Tables for Sheds and Garages in Canada

Which Code Applies to a Shed or Garage in Canada?

Building codes in Canada are adopted provincially, not federally. The National Building Code of Canada (NBC) published by the National Research Council is a model code that provinces adopt, often with modifications. For residential accessory structures — sheds, detached garages, workshops — Part 9 of the NBC ("Housing and Small Buildings") applies when the structure is less than three storeys and has a building area below the Part 3/Part 9 threshold.

In practice, most detached garages and all backyard sheds fall within Part 9 scope. Some municipalities have additional bylaws governing maximum accessory structure footprint, setbacks, and height, which operate alongside the building code but are separate from structural requirements.

When a building permit is not required — which varies by province and municipality, and sometimes by structure size — there is no mandatory code compliance. However, Part 9 span tables remain useful as a baseline for structural adequacy even on unpermitted work.

The NBC Part 9 Span Tables

Part 9 of the NBC contains prescriptive span tables covering floor joists, ceiling joists, roof rafters, and lintels (headers). These tables are the starting point for most residential accessory structure framing in Canada. The tables assume:

• S-P-F or D.Fir-L species (tables are usually species-specific)
• No. 2 or Select Structural visual grade (or equivalent MSR values)
• S-DRY moisture condition (19% MC or below)
• Standard loading conditions as defined in the code (live load, dead load, snow load for roofs)

Floor Joists

Part 9 floor joist tables are organized by:

• Supported load (residential floor live load is typically 1.9 kPa, with a 40 psf live load assumption in many tables)
• Joist spacing (305 mm / 12 in., 400 mm / 16 in., 600 mm / 24 in.)
• Species and grade

For a shed floor intended to support tools and equipment — rather than a habitable residential floor — the applicable live load assumption should be confirmed with the local building department, as some jurisdictions apply a higher load for storage use.

Roof Rafters

Rafter span tables in Part 9 are organized by snow load zone. Canada's snow loads vary significantly by geography: southern Ontario and the Lower Mainland of B.C. have lower ground snow loads than the interior of B.C., northern Ontario, Quebec, or the Prairie provinces at altitude. The NBC includes a snow load map, and provincial supplements update it for local conditions.

The rafter span is measured along the horizontal projection of the rafter (the "run"), not along the actual sloped length. Specifying the wrong measurement is a common source of error when reading rafter tables.

Headers and Lintels

NBC Part 9 provides lintel tables for headers over door and window openings in load-bearing walls. These tables specify header size based on:

• Opening width
• Number of storeys supported above
• Species and grade

For a single-storey detached garage, the loading conditions are relatively modest, and standard doubled 2×10 or 2×12 headers typically satisfy the tables for openings up to standard garage door widths. However, wide openings — single-car doors at 2.4 m (8 ft) or double-car doors at 4.8 m (16 ft) — merit careful table lookup or an engineered beam.

Provincial Modifications

Each province publishes a provincial supplement to the NBC that modifies or replaces certain provisions. The most common modifications affecting span tables for accessory structures include:

• Snow load adjustments — Provincial supplements update ground snow load values for local stations, which directly affects rafter span limits.
• Wind load zones — Some provinces modify wind pressure assumptions, which can affect roof sheathing and fastening requirements.
• Local authority requirements — Municipalities in seismic zones (parts of B.C. and the Yukon) may impose additional requirements not in Part 9 for even small accessory structures.

Reference Span Values — S-P-F No. 2, Standard Spacing

The values below are illustrative extracts from the 2015 NBC Part 9 tables for S-P-F No. 2 lumber under standard residential floor loading and a representative snow load category. These are for reference orientation only — always use the current table applicable in your jurisdiction and confirm inputs match your design conditions.

Specific span values are not reproduced here because they depend on species, grade, loading condition, and snow zone — all of which must be confirmed for the project location. The NBC tables are available through the National Research Council's Codes Canada portal and through most provincial building code authorities.

CMHC's Wood-Frame House Construction Guide

For builders working on residential accessory structures without ready access to the NBC tables, CMHC's Wood-Frame House Construction (BP 5) provides a simplified treatment of Part 9 framing requirements, including span table summaries and worked examples. CMHC makes this publication available through its website as a free download. The guide is aligned with Part 9 of the NBC but presents material in a more accessible format for non-engineers.

The CMHC guide also includes sections on framing connections, fastener schedules, and sheathing requirements that are relevant to shed and garage construction but not always covered in detail in the span tables themselves.

When to Consult an Engineer

Part 9 prescriptive span tables are designed to cover common cases without engineering input. However, several conditions push a project outside the tables' assumptions:

• Large unsupported spans (e.g., a single-bay garage wider than about 7.3 m / 24 ft without an interior bearing wall)
• Heavy storage loads significantly above residential live load assumptions
• High snow load zones (many locations in Alberta, B.C. interior, and northern provinces)
• Unusual roof shapes (shed roofs at shallow pitches, or asymmetric roof forms) that generate loads outside the table assumptions
• Any structure where a local building official requires an engineered design as a condition of permit

In these cases, the prescriptive tables serve as a starting point for engineering review, not a final answer.

Finding the Official Tables

The authoritative source for NBC Part 9 span tables is the NBC itself, available through the NRC Codes Canada portal. Provincial supplements are available through each province's building standards authority. Municipal building departments can confirm which edition of the code and which provincial supplement are in force for permit applications in their jurisdiction.