2024 code changes: the pillar guide

What Changed in the 2024 Ontario Building Code: the 1,730 Amendments That Matter

The 2024 Ontario Building Code carries about 1,730 amendments, mapped in MMAH's 118-page Technical Bulletins. Highlights: 'house' is no longer a defined term while 'secondary suite' is; framing spacings move to soft-converted metric values (305/406/610 mm become 300/400/600 mm); new stair, guard and fire-separation rules land in Part 9; farm buildings get a new Part 2; and articles were mass-renumbered.

How big is the change, really?

Bigger than a normal code cycle. The 2024 Building Code is not an edit of the 2012 code: it adopts the 2020 National Building Code of Canada, amended by the "Ontario Amendments to the National Building Code of Canada 2020" (dated May 15, 2024). MMAH's own framing is that this eliminates at least 1,730 technical variations between the provincial and national requirements. The new code took effect January 1, 2025, and the qualification exams followed on March 30, 2026. Since that date, all 16 BCIN exams are based on the 2024 code.

For candidates, the practical consequence is blunt: 2012-era study material, memorized article numbers, and old cross-reference sheets are now unreliable. This guide maps the changes that matter most, with article numbers.

Where are the changes documented?

The primary document is MMAH's 2024 Building Code Technical Bulletins: Highlights of Key Changes (July 2024): 118 pages, organized as one bulletin per Part of the code, written specifically to help users navigate the new Compendium. It is guidance, not law. Where the bulletin and the Compendium text disagree, the Compendium governs. MMAH also publishes a free syllabus for each of the 16 exams on the ontario.ca study-guides page, which tells you which Parts your exam actually draws from.

Is 'house' still a defined term?

No, and this is the terminology flip that trips people. The 2024 code deletes the defined term "house" and adds "secondary suite". Throughout Part 9, provisions that used to say "house" now say "secondary suite," "a house with a secondary suite," or "individual dwelling unit." The bulletin gives the new definition: a secondary suite is a self-contained dwelling unit located in a building (or portion of one) of only residential occupancy that contains only one other dwelling unit and common spaces, where both dwelling units constitute a single real estate entity.

Other definition changes in Division A: agricultural occupancy, greenhouse agricultural occupancy, high-hazard agricultural occupancy, combustible dusts, protected floor space, ramp, and underpinning are new; farm building, heritage building, and post disaster building were amended. If you search a PDF for "house," you will now miss provisions. Our guide to secondary suites in the 2024 code goes deeper.

What happened to framing spacings?

The familiar 2012 numbers (305 mm, 406 mm, and 610 mm, the hard metric conversions of 12, 16, and 24 inches) become 300 mm, 400 mm, and 600 mm in the 2024 code, following the national soft-conversion approach. The bulletin notes that for framing dimensions both conversions are intended to be acceptable, but the numbers printed in Part 9 tables and provisions are now 300/400/600. If your instinct is to scan for "406," retrain it.

What are the new stair and guard rules in Part 9?

Section 9.8 saw both new requirements and heavy renumbering:

• Open risers are banned: new Article 9.8.4.9. Open stair risers are prohibited in Part 9 buildings with limited exceptions, consistent with the Part 3 requirement. This article has no 2012 equivalent.
• The 150 mm sphere rule: new Sentence 9.8.8.5.(2). Except for guards serving industrial occupancies, the triangular openings formed by stair risers, treads, and the bottom element of a required guard must be small enough to prevent passage of a 150 mm diameter sphere.
• Secondary-suite headroom: new Sentence 9.8.2.2.(4). A minimum clear height of 1 850 mm is permitted over stairs under beams and ducts in secondary suites.
• Renumbering: former 9.8.4.4A (uniformity of runs with mixed treads) is now 9.8.4.5, Winders moved from 9.8.4.5 to 9.8.4.6, and spiral stairs from 9.8.4.5A to 9.8.4.7. The full chain is in our old-to-new article renumbering map.

What changed in fire protection?

The headline change for dwelling work is in Sentence 9.10.9.16.(4): the separation between the dwelling units (and their common spaces) in a house with a secondary suite may now be built as a smoke-tight barrier of not less than 15.9 mm Type X gypsum board, in lieu of the fire separation with a 45-minute fire-resistance rating the 2012 code required. Note the number itself is new too: this provision lived at 9.10.9.14 in the 2012 code. In fact the whole fire-separation block from old 9.10.9.8 onward shifted down by two places, and the penetration articles (9.10.9.6 through 9.10.9.9) were rewritten for harmony with the 2020 NBC.

What is entirely new? Part 2 farm buildings

Division B, Part 2 (previously reserved) now applies to all farm buildings, and the code introduces Group G, a new agricultural occupancy classification, with a threshold at 600 m² and 3 storeys shaping how requirements apply. Division A was amended to match: former Article 1.3.1.2 was relocated to 1.3.3.1A to direct farm buildings into Part 2. This is brand-new exam territory that no 2012-era study aid covers; we break it down in the new Part 2 for farm buildings.

Why do your old article references miss?

Because the 2024 code renumbers articles to align with the 2020 NBC's numbering system, reserving letter-suffixed numbers (like 9.10.14.3A) for Ontario-only provisions. Some moves are subtle and dangerous: 9.8.4.5 used to be Winders and is now uniformity of runs; 9.10.1.2 used to be Sloped Roofs, whose content is now at 9.10.1.1. A citation that "still works" can silently point at the wrong provision: the worst possible failure mode in an open-book exam. The renumbering map tables the verified old-to-new pairs.

Why does this matter for the open-book BCIN exams?

Every BCIN exam is open book (70 questions in 3 hours, about 2.5 minutes per question), so the scored skill is navigating the 2024 Compendium fast. The ~1,730 amendments attack exactly that skill: terminology you would search for is gone ("house"), numbers you memorized moved, and new provisions exist where 2012 instincts say nothing does. Candidates for the House exam are the most exposed, since Part 9 absorbed so much of the change; the BCIN House exam guide covers what that exam looks like now. Whatever you write, prepare on 2024-native material. Practising on 2012-based questions actively trains the wrong reflexes.

FAQ

Sources: MMAH 2024 Building Code Technical Bulletins: Highlights of Key Changes (July 2024); ontario.ca 2024 Building Code study-guide pages; Humber Polytechnic examination pages. Last reviewed 2026-08-14. Found an error? Tell us and we'll fix it.