OBC 2024 stair changes — what shifted from OBC 2017.
Ontario's 2024 Building Code update aligned several stair and egress provisions with NBCC 2020 reference values. For new construction, the differences mostly land at the margin. For existing-building retrofits, a few of the changes can flip a previously-compliant stair into one that needs work — and they're the changes worth knowing before the next permit.
The big-picture shift: harmonization with NBCC
OBC 2024 brought Ontario into closer alignment with the 2020 National Building Code. Most stair-relevant provisions in §3.4 (Means of Egress) and §3.3 (Safety Within Floor Areas) now reference or mirror NBCC values directly rather than carrying Ontario-specific divergent figures. For fabricators, this is good news: a stair that's NBCC-compliant in one province is generally OBC-compliant in Ontario without separate detailing.
1. Egress width calculation
OBC §3.4.3 retains the occupant-load × per-occupant-width-factor formula but updated the factors for some occupancy groups. For most industrial / business occupancies (Group D, E, F2, F3), the practical figure for a typical stair lands at 1100 mm (43") clear width — same as before. The change shows up in larger assembly occupancies where the per-occupant factor is lower than 2017 figures.
2. Riser / run alignment
OBC 2024 §3.4.6.4 sets stair geometry as:
- Maximum riser: 200 mm (7-7/8")
- Minimum tread run: 230 mm (9") for industrial / business; 255 mm (10") for assembly / mercantile
- Maximum 16 risers per flight before a landing is required
- Headroom: 2050 mm (6'-9") clear
OBC 2017 had similar but slightly different figures in some sub-clauses. New designs after the 2024 transition use the §3.4.6.4 numbers above.
3. Guard load harmonization
OBC §3.3.1.18 (Guards) and §4.1.5.14 (Guard loads) now both reference the same 200 lb (1.0 kN) concentrated top-rail load and the same 50 lb/ft (0.7 kN/m) uniform top-rail load. In OBC 2017, the cross-references between these sections were not always consistent in practice; the 2024 text closes that.
4. Existing-building reviews
Here's where the retrofit math gets interesting. OBC 2024 doesn't retroactively void stairs built under earlier code editions — grandfathering still applies. But several triggers can re-open a code review on existing stairs:
- Change of occupancy — moving from Group F (industrial) to Group D (business) or E (mercantile) can shift the egress width calculation. A stair that was compliant for industrial use may not be for the new occupancy.
- Major renovation — defined by floor-area threshold; can trigger application of current code to the egress system.
- Change of use within the same occupancy group — sometimes triggers, sometimes doesn't, depending on how the new use loads the egress path.
- New permit-bound work — adding a mezzanine, for instance, runs current code on the new structure and can require alignment of the existing egress.
What to do before next permit
If you have an existing stair that was last reviewed under OBC 2017 or earlier, and you're planning permit-bound work in the same building, ask three questions at site measure:
- Does the existing stair meet OBC 2024 width for the building's current occupant load?
- Are riser / run dimensions within §3.4.6.4 limits?
- Is the guard system to current §3.3.1.18 standards (height, infill, top-rail load)?
If any answer is no, the existing stair may need work as part of the new permit. Catching it at site measure is much cheaper than at inspection.
Where to verify
OBC 2024 is published as Ontario Regulation 332/12 amended; the current consolidated version is on ontario.ca/laws. NBCC 2020 reference text is from the National Research Council. We cite specific sub-clauses on every drawing we stamp; if a clause has changed since the original drawings, we'll flag it before fabrication starts.