Canadian Structural Steel Codes: CSA S16 and the Building Code

In Canada, structural steel is designed to CSA S16, "Design of steel structures," because the building code says so. The National Building Code of Canada (NBC) and the provincial codes based on it, including Ontario's, state that buildings and structural members made of structural steel shall conform to CSA S16. The 2024 Ontario Building Code references CSA S16-19. Around S16 sits a family of other standards for steel material, welding, cold-formed members and fire ratings.

If you've been asked for "code-compliant steel" and aren't sure what that covers, this is the map.

How the codes and standards fit together

Think of it as a chain. The building code is law. It sets loads and fire requirements, then hands off the detailed design of each material to a CSA standard. Those standards in turn reference material and welding standards.

In the 2024 OBC, the design hand-offs are in Division B, Subsection 4.3.4: Article 4.3.4.1 for structural steel (CSA S16), Article 4.3.4.2 for cold-formed steel (CSA S136) and Article 4.3.4.3, which requires steel building systems to be made by companies certified to CSA A660. Masonry and concrete are handed off the same way, to CSA S304 and CSA A23.3.

What CSA S16 covers

CSA S16 is a limit states design standard. The engineer multiplies the loads by load factors from the building code, then checks that the factored resistance of each member and connection is at least as large. For structural steel, the standard resistance factor applied to yield-governed resistances is 0.90.

The standard covers, broadly:

• Members: tension members, columns, beams, beam-columns, composite beams and built-up members, including buckling and lateral-torsional buckling.
• Connections: bolts, welds, bearing, block shear and connection plates.
• Seismic design: the ductile and limited-ductility frames that the building code's seismic tables assign to steel. The OBC's table of seismic force resisting systems lists each steel system "designed and detailed according to CSA S16."
• Serviceability: deflection and vibration guidance.
• Fabrication, erection and quality: tolerances, shop drawings, welding and inspection requirements.

That last point matters to contractors. S16 isn't only a calculation manual for engineers. The Ontario code's explanatory note to Article 4.3.4.1 points out that qualification for fabricators and erectors of welded construction is found in Clause 24.3 of CSA S16. That clause is what links structural steel to CWB company certification. We explain how that works in why hire a CWB-certified fabricator.

Which edition applies

This trips people up, because standards are updated more often than codes are adopted.

• The NBC 2020 and the 2024 OBC both reference CSA S16-19.
• A newer edition of S16 has since been published. The Canadian Institute of Steel Construction (CISC) reproduces it in the 13th edition of its Handbook of Steel Construction, which is intended for use with the 2025 National Building Code. The 12th edition handbook contains S16-19.
• The edition that governs your permit is the one referenced by the code in force for that project. Provinces adopt new national code editions on their own schedule, with their own amendments.

In practice, your engineer of record decides which edition the design follows and states it on the drawings. If you're a contractor or owner, the useful check is simply that the structural drawings name the standards, and that the fabricator works to the same ones.

Part 9 houses vs Part 4 engineered buildings

The OBC splits buildings into two structural tracks, and steel shows up in both.

Part 9 covers houses and small buildings: three storeys or less and a building area of up to 600 m², in certain occupancy groups. Here the code itself contains prescriptive steel rules, so a small job can sometimes be sized without a structural calculation:

• Steel floor beams come from Table 9.23.4.3 and Tables 9.23.4.3.-A to -J, which list W-shapes only and require the beams to at least meet Grade 350W of CSA G40.21. See our steel beam span tables for Ontario homes.
• Steel lintels come from Article 9.20.5.2 and its three tables.
• Columns follow Section 9.17, including adjustable columns to CAN/CGSB-7.2 up to 36 kN.

Part 4 covers everything else, and any Part 9 element the prescriptive tables don't fit. Here the steel is designed by an engineer to CSA S16, with loads from Part 4. A long-span basement beam carrying a point load from above is a Part 4 design even in a house.

Material standards: what the steel has to be

The design standard assumes the steel has certain properties. Material standards guarantee them.

• CSA G40.20/G40.21, "Structural quality steel," is the Canadian standard for structural plate, shapes, hollow structural sections and bars. Grades are named by minimum yield strength in MPa, such as 300W and 350W, where W means weldable.
• ASTM standards are also widely used in Canada. The member tables in the 12th edition CISC Handbook are based on ASTM A992, A572 Grade 50, A913 Grade 65, A500 Grade C and CSA G40.21 350W.
• HSS can be made to CSA G40.21 (Class C or Class H) or to ASTM A500, and the difference affects design properties such as the wall thickness used in calculations.

Mill test certificates are how a supplier shows that the steel delivered matches the grade specified. If your project specification asks for them, say so when you order.

Welding standards: W59 and W47.1

Two CSA welding standards sit underneath S16:

• CSA W59, "Welded steel construction," covers how structural welds are designed, made and inspected. See our guide to CSA W59.
• CSA W47.1 covers certification of companies that weld steel, administered by the Canadian Welding Bureau. Division 1 and Division 2 companies can take responsibility for welded structural work.

The building code doesn't name W59 or W47.1 directly. It names S16, and S16 brings them in.

Fire, galvanizing and the rest

A few other requirements land on steel jobs regularly:

• Fire resistance. Where the building code requires a fire-resistance rating, the OBC (Article 3.1.7.1) accepts either a test to CAN/ULC-S101 or an assigned rating from Supplementary Standard SB-2, which includes tables for protected steel columns and beams. Whether a steel member needs protection at all is a separate question, covered in does structural steel need fireproofing in Ontario?
• Coatings. Part 9 requires steel lintels supporting masonry to be prime painted or otherwise protected, and exterior steel columns to have rust-inhibitive paint. Larger projects follow the specification, which may call for hot-dip galvanizing.
• Industry practice. The CISC Code of Standard Practice for Structural Steel isn't law, but specifications often reference it to define what's included in "structural steel," who supplies what and how shop drawings are approved. The current 10th edition is part of the 13th edition Handbook.

Getting copies of the codes and standards

• Ontario Building Code: the Building Code Compendium is available from Publications Ontario, and the regulation itself (O. Reg. 163/24) is on e-Laws.
• National Building Code: the National Research Council makes its code documents available as free downloads.
• CSA S16, S136, W59, W47.1, G40.21: sold by CSA Group. S16 and its commentary are also reproduced in the CISC Handbook of Steel Construction, which most Canadian steel designers keep on the desk.

Free "structural steel code PDF" downloads circulating online are often outdated editions or US documents. Work from the edition your engineer names.

Steel built to the drawings and the standards

The engineer chooses the standards; the fabricator has to build to them. Our shop welding is certified by the Canadian Welding Bureau, our shop drawings are done in-house, and engineering services are available for projects that need them. For a look at the fabrication side of the standards, see steel fabrication standards in Canada.

Send us your structural drawings for a free take-off and quote, or browse the steel products we supply and fabricate.