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OBC 2024 stair code, in plain language.

A working summary of the Ontario Building Code 2024 stair rules every facility manager and GC needs in front of them before a stair is drawn — width, rise, run, landings, guards, and load. This is a working reference, not a substitute for the actual code; cite the linked sections directly on permit drawings.

Where stairs sit in the code

Part 3 vs Part 9.

OBC 2024 splits buildings into two main paths. Part 3 covers commercial, institutional, industrial, and high-rise residential — anything with assembly, business, mercantile, industrial (Group A, B, D, E, F) occupancy. Part 9 covers low-rise residential. The stair rules diverge between them: Part 3 is more demanding on width, load, and guard height; Part 9 is more permissive in those areas but stricter in some others. Most of our work is Part 3; some renovation projects fall under Part 9.

Quick reference — OBC §3.4.6 stairs in exits

Max riser height (Part 3)200 mm
Min tread run255 mm typical (occupancy-dependent)
Max risers per flight16 (~9 ft rise)
Min flight widthper occupant load × width factor (§3.4.3) — typically 1100 mm
Headroom2050 mm clear (§3.4.3.4)
Landing depth≥ flight width
Live load4.8 kPa + 1.3 kN concentrated (NBCC §4.1.5)

OBC §3.3.1.18 — Guards

Guard height (Part 3)1070 mm (42")
Guard height (Part 9 dwelling)900 mm typical; 1070 mm if > 1800 mm above grade
Top-rail load0.9 kN non-public / 1.0 kN public (NBCC §4.1.5.14)
Sphere test100 mm max opening (where required)
Mid-railrequired where vertical pickets > 100 mm apart

When the rules apply

OBC §3.4 ("Means of Egress") applies to any stair carrying occupant load — commercial egress, mezzanine access serving an occupied platform, fire-escape retrofit. Egress staircases are the textbook case. Where the stair is purely service or maintenance access — ship's ladders, cage ladders to a tank top — the egress rules don't apply, but the structural and guard rules still do.

Common compliance traps

Adding a mezzanine to an existing building — the platform's occupant load can trigger a second-egress requirement that didn't apply before. See mezzanine access stairs.
Change of use — moving from storage (Group F) to assembly or production resets the occupant-load and egress calculations.
Rise > 16 risers in a single flight — needs an intermediate landing; usually triggers switchback geometry.
Inadequate headroom under existing duct or beam — 2050 mm is non-negotiable; a stair that meets every other rule fails on this.
Specifying a ship's ladder for general egress — not permitted; rebuild as a code-compliant stair.
Residential stairs in a Part-3 conversion — converted multi-unit buildings often inherit a 36" guard that no longer meets §3.3.1.18.

Frequently asked

What stair width does OBC 2024 require?

For a means-of-egress stair under OBC Part 3, the required width is calculated from occupant load times a per-occupant width factor (§3.4.3). Industrial buildings typically land at 1100 mm (43") clear width; the actual figure goes on the stamped drawing alongside the occupant-load calculation it came from.

What's the maximum riser height under OBC §3.4.6?

For stairs in exits under OBC 2024 Part 3, the maximum riser is 200 mm (7-7/8"). Minimum tread run is 255 mm (10") for most occupancies in exits; specific use groups (industrial Group F2/F3) permit narrower runs under §3.4.6.4. Verify the exact figure for your project's use group against the current code text. Risers and treads must be uniform within a flight — variation is a fail at inspection.

How many risers are allowed in a single flight?

Maximum 16 risers between landings under OBC §3.4.6 (and 18 risers for some public-access stairs) — roughly 9 ft of rise. Above that, an intermediate landing is required, which usually means a switchback or stacked-flight configuration.

What's the minimum headroom on a stair?

OBC §3.4.3.4 requires 2050 mm (6'-9") clear headroom over a stair, measured plumb from the leading edge of the tread. This catches a lot of basement-renovation stairs that meet every other rule but trip on headroom under existing duct.

What guard height is required at a stair or mezzanine edge?

OBC §3.3.1.18 requires 1070 mm (42") guards at mezzanines and stair landings in commercial / industrial buildings (Part 3). Residential (Part 9) is typically 900 mm for dwelling-unit guards, rising to 1070 mm where the guard is more than 1800 mm above grade. Guards must withstand a concentrated load at any point along the top rail per NBCC §4.1.5.14: 0.9 kN (~200 lb) non-public, 1.0 kN (~225 lb) for places of public access.

Can a ship's ladder be used as an egress stair?

No. OBC §3.4.6 permits steep-pitch alternative stairs only for limited equipment-access situations — not for serving general occupant load. See ship's ladders for the approved use cases.

What live load does an industrial stair need to carry?

NBCC Table 4.1.5.3 sets stair live load at 4.8 kPa (100 psf) uniform plus a 1.3 kN concentrated load. Mezzanine decks are higher — typically 4.8 to 24 kPa depending on use. The stair itself rarely governs.

When does OBC trigger a second egress stair?

OBC §3.4.2 sets the threshold for two means of egress based on travel distance, occupant load, and use group. For most warehouse pick-mezzanines under ~60 occupants, a single stair is sufficient. Larger platforms typically need a second stair, a pallet-drop with separate access, or a floor-edge ladder. We calculate this on every project at site measure.

// Working reference, not a permit document

This page summarizes the OBC 2024 stair rules that come up most often on industrial and commercial projects. It does not replace the code itself or the stamped drawings that go on a permit submission. Section numbers cited above point to the actual code clauses; verify each clause in the official OBC 2024 against your project's specific use group and occupancy. We provide the stamped drawings as part of every quote.

Steel stairs & industrial stair systems pillar
Egress staircases — code-required exit stairs
Mezzanine access stairs — second-exit thresholds
Stair cost guide — what the configurations actually cost