Take a breath: the NBC 2020 Part 3 versus Part 9 boundary feels intimidating on paper, but it comes down to one applicability rule that you can know cold. NBC 2020 Part 3 covers Fire Protection, Occupant Safety and Accessibility for buildings that exceed Part 9 thresholds or contain Group A, B, or F1 occupancies. NBC 2020 Part 9, Housing and Small Buildings, applies only when a building is three storeys or fewer in building height, 600 square metres or less in building area, and used for Group C, D, E, F2, or F3. In our years of working with Intern Architects through every ExAC sitting, our team has seen that deciding which Part applies is the first move on most Section 2 scenarios, so this is the walkthrough we share with candidates at Examitect, an independent ExAC prep platform unaffiliated with the CACB. Get the boundary right once, and Section 2 stops feeling like a code maze.
| Topic | NBC 2020 Part 3 vs Part 9 |
|---|---|
| Exam | ExAC Section 2 (Codes) |
| Code | National Building Code of Canada 2020, Division B |
| Part 3 title | Fire Protection, Occupant Safety and Accessibility |
| Part 9 title | Housing and Small Buildings |
| Applicability rule | Division A, Sentence 1.3.3.2.(1) |
| Part 9 limit | Three storeys, 600 square metres, Group C, D, E, F2, F3 only |
| Open book | Yes: NBC 2020 and NECB 2020 are permitted in Section 2 |
| Best for | Intern Architects preparing for the ExAC Section 2 |
The National Building Code of Canada is organised into two Divisions and several Parts. Division A sets out the compliance, objectives, and applicability rules; Division B is the technical code. Within Division B, the Parts cover discrete topics: Part 3 carries fire safety and occupant safety, Part 4 carries structural design, Part 5 carries environmental separation, and so on. Part 9 sits beside the others but is structured differently: it is a self-contained code for housing and small buildings, with its own structural, envelope, fire, plumbing, and energy rules built in.
Part 3 (Fire Protection, Occupant Safety and Accessibility) is the section ExAC Section 2 candidates spend most of their study time inside. It contains the rules for major occupancy classification, fire resistance ratings, spatial separation, exits, fire alarms and detection, smoke control, and barrier-free design. Anything taller than three storeys, larger than 600 square metres, or used for assembly, institutional, or high-hazard industrial occupancies, is governed here.
Part 9 (Housing and Small Buildings) is the smaller, simpler code path for buildings that fit inside its applicability box. A two-storey single-family home, a small office over a corner store, a four-unit row house with a building area under 600 square metres: these are Part 9 buildings. Part 9 is not a shortcut; it is a complete set of prescriptive rules calibrated to smaller, simpler buildings where the full Part 3 to Part 7 framework would be unnecessary overhead.
Knowing which Part applies is the foundational building code fundamentals move in Canadian practice. Get the Part wrong and every clause you cite is wrong with it.
The rule that decides Part 3 versus Part 9 lives in Division A, Sentence 1.3.3.2.(1) of NBC 2020. A building falls under Part 9 only when all three of the following are true: it is three storeys or fewer in building height; it has a building area of 600 square metres or less; and it is used for one of the occupancies Part 9 covers (Group C residential, Group D business and personal services, Group E mercantile, Group F2 medium-hazard industrial, or Group F3 low-hazard industrial). If any one of the three conditions is exceeded, the building is designed to Part 3.
Three things to read carefully in that rule. First, the storey count is building height, a defined term in NBC 2020 Division A; it is not the same as the number of physical floors and can be lower than a layperson's count when basements and the like are excluded. Second, the 600 square metre limit is building area, also a defined term, measured at the largest horizontal area between exterior walls. Third, Group A (assembly), Group B (care, treatment, or detention), and Group F1 (high-hazard industrial) are not on the Part 9 list at all; any building containing one of those occupancies goes to Part 3 regardless of size.
If the scenario lists Group A, Group B, or Group F1, the answer is Part 3. Stop here.
Confirm storeys (building height, defined term). More than three storeys means Part 3.
Confirm the square metres (building area, defined term). More than 600 square metres means Part 3.
If occupancy, height, and area all fit inside the Part 9 box, the building can be designed to Part 9.
Memorise that sequence; it is one of the few NBC moves worth committing to recall. The applicability rule is asked, directly or indirectly, on most Section 2 sittings.
Part 3 is the largest single Part of NBC 2020 Division B and the one most often opened in a Section 2 exam booklet. The Subsections it contains map closely to the topics ExAC Section 2 examines, which is why the Part 3 tab block deserves the largest share of your tabbing strategy.
The ExAC questions that hit Part 3 hardest are the fire and life safety ones in Subsection 3.2, spatial separation in 3.2.3, exits in 3.4, and barrier-free in 3.8. If your study runway is short, those four Subsections are the priority.
Part 9 is its own world. It is a self-contained code, with structure, envelope, plumbing, energy, and fire all rolled into one Part. The Sections are numbered 9.1 to 9.37 and read like a small standalone manual for housing and small commercial buildings.
Part 9 has the reputation of being the simpler Part to study, and it is, but ExAC candidates underestimate how many of its rules differ from Part 3 in subtle ways. The spatial separation tables, the fire resistance rating shortcuts, and the energy compliance path are all Part 9 specific. Treat Part 9 as its own block of study, not as a stripped version of Part 3.
The small buildings topic page covers Part 9 in study-card form, and the NBC 2020 Part 9 Illustrated user guide reference gives you a diagram-led study companion you can keep at home (it is not permitted in the exam room, but it earns its keep during prep).
The table below is the comparison ExAC candidates most often need: the same questions answered for both Parts. Use it to calibrate where the two diverge and where they overlap.
| Dimension | NBC 2020 Part 3 | NBC 2020 Part 9 |
|---|---|---|
| Title | Fire Protection, Occupant Safety and Accessibility | Housing and Small Buildings |
| Applies when | Building exceeds Part 9 thresholds, or contains Group A, B, or F1 | Three storeys or fewer, 600 m² or less, Group C, D, E, F2, or F3 only |
| Scope | Fire and life safety, exiting, accessibility (Subsection 3.8 carries it) | Self-contained: structure, envelope, fire, plumbing, energy, all in Part 9 |
| Spatial separation | Subsection 3.2.3, with limiting distance and unprotected opening tables | Subsection 9.10.14 and 9.10.15, with Part 9 specific tables |
| Fire resistance ratings | Subsection 3.2.2 and tied to construction type | Subsection 9.10, simplified and tied to occupancy and storey count |
| Accessibility | Section 3.8 (most ExAC content lives here) | Section 9.5 carries a smaller barrier-free set for Part 9 buildings |
| Structural design | Out of scope (Part 3); structural rules live in Part 4 | Inside Part 9: Sections 9.3 and 9.4 carry prescriptive structural rules |
| Envelope | Out of scope (Part 3); envelope rules live in Part 5 | Inside Part 9: Section 9.25 carries thermal, air, and vapour rules |
| Energy | NECB 2020 applies | Section 9.36 is the prescriptive Part 9 path (NECB 2020 is an alternative) |
| Plumbing | Out of scope (Part 3); plumbing rules live in Part 7 | Inside Part 9: Section 9.31 carries plumbing for small buildings |
| Heavier ExAC weight | Yes, roughly two thirds of Section 2 code questions | Roughly one third, often on applicability or small-building scenarios |
Two takeaways from this table. First, Part 3 is narrower than candidates think; structural, envelope, energy, and plumbing are not inside it (they live in Parts 4, 5, NECB 2020, and 7). Second, Part 9 is wider than candidates think; it carries its own structural, envelope, plumbing, and energy rules in one Part. Confusing the two is the most common boundary error on Section 2.
Most exam scenarios are clearly one Part or the other. The boundary cases are where candidates lose marks, and they tend to come up in two patterns.
A two-storey building with retail on the ground floor (Group E mercantile) and residential dwelling units above (Group C) is the classic Part 9 candidate, because it is under three storeys and under 600 square metres, and both occupancies are on the Part 9 list. But if the retail were a small bar or restaurant assembling more than the assembly-occupancy threshold of occupants, that ground floor reclassifies to Group A2; the building now contains a Group A occupancy and is designed to Part 3, even though it is still small. The boundary moves with the occupancy, not the floor plate.
A building that meets the Part 9 applicability test can still be designed to Part 3 if the designer chooses. The reverse is not true: a Part 3 building cannot be designed to Part 9. On the ExAC, the scenario will typically tell you which Part the design team has chosen; if it does not, default to the smallest Part that the rule allows. Designing a single-family home to Part 3 is legal but unusual; designing a 1,200 square metre warehouse to Part 9 is not allowed.
This is the boundary that working interns most often misread. A four-storey wood-frame apartment building is Part 3, not Part 9, because building height exceeds three storeys. The encapsulated mass timber and combustible mid-rise provisions in Subsection 3.2.2 govern the construction. If the scenario says "five-storey wood-frame residential", reach for Part 3 and stay there.
Every ExAC cycle, the same handful of Part 3 versus Part 9 mistakes show up in the post-exam debriefs our team runs with candidates. Reading them now is cheaper than discovering them in the exam room.
Section 2 is open book. The candidates who pass it efficiently are the ones who can find the right clause in under 30 seconds. The tabbing block below is the minimum viable set for the Part 3 / Part 9 boundary; pair it with the wider tabbing approach in the ExAC open-book tabbing strategy post.
Place a single high-visibility tab on Division A, Sentence 1.3.3.2.(1). This is the rule that decides Part 3 versus Part 9; every question that turns on the boundary points back here. A candidate who can land on 1.3.3.2.(1) in under five seconds rarely picks the wrong Part on the rest of the exam.
Skip tabbing every Section. Tabs that exist but never get used cost time at the desk because the eye has to filter past them. The minimum viable set above is intentional: it covers most Section 2 questions and leaves space for a handful of personal additions based on the topics you struggle with in practice.
NBC 2020 Part 3 is the Division B Part titled Fire Protection, Occupant Safety and Accessibility. It applies to all buildings that exceed the size or occupancy limits of Part 9, and to any building that contains a Group A, Group B, or Group F1 major occupancy. Part 3 carries the bulk of the fire safety, spatial separation, exiting, and accessibility requirements tested on ExAC Section 2.
NBC 2020 Part 9 is the Division B Part titled Housing and Small Buildings. It applies to buildings of three storeys or fewer in building height, with a building area not exceeding 600 square metres, and used for residential, business and personal services, mercantile, or medium and low-hazard industrial occupancies. Part 9 contains its own prescriptive rules for structure, envelope, fire safety, and energy, written for smaller and simpler buildings.
Apply the Part 9 applicability rule from NBC 2020 Sentence 1.3.3.2.(1) of Division A: a building falls under Part 9 only when it is three storeys or fewer in building height, has a building area of 600 square metres or less, and is used for one of the occupancies Part 9 covers (Group C, D, E, F2, or F3). If the building exceeds any of those thresholds or contains a Group A, B, or F1 occupancy, it is designed to Part 3.
A four-storey wood-frame apartment is designed to Part 3, not Part 9. Part 9 stops at three storeys in building height. Mid-rise wood Group C buildings (four to six storeys of wood construction) fall under Part 3 and use Part 3 rules for fire resistance ratings, spatial separation, exiting, and structural design, with the encapsulated mass timber and combustible construction provisions of Subsection 3.2.2 setting the limits.
Yes, Part 9 covers fire and life safety, but with its own prescriptive rules written for small buildings. Section 9.10 (Fire Protection) sets the fire resistance ratings, spatial separation, exits, and smoke alarm requirements that apply to Part 9 buildings. The Part 9 rules are typically simpler and more permissive than Part 3 because the buildings are smaller and the occupant loads lower.
Yes, Part 9 covers spatial separation in Subsection 9.10.14 and 9.10.15. The rules use limiting distance, exposing building face area, and unprotected opening percentages, like Part 3, but the tables are calibrated for small residential and small commercial buildings. ExAC candidates working on a Part 9 spatial separation scenario must use the Part 9 tables, not the Part 3 tables in Subsection 3.2.3.
Accessibility requirements for buildings of public assembly, business, mercantile, and most non-residential occupancies live in NBC 2020 Section 3.8, inside Part 3. Part 9 contains a small set of barrier-free provisions in Section 9.5 for the housing and small-buildings scope it covers, but most accessibility content tested on ExAC Section 2 sits in Section 3.8. Provincial accessibility regulations may add further requirements on top of the NBC.
ExAC Section 2 covers NBC 2020 Division A (compliance, objectives, and applicability) and the parts of Division B most often used in practice: Part 3 (Fire Protection, Occupant Safety and Accessibility), Part 4 (Structural Design at an awareness level), Part 5 (Environmental Separation), Part 6 (Heating, Ventilating and Air Conditioning at an awareness level), Part 7 (Plumbing at an awareness level), and Part 9 (Housing and Small Buildings). NECB 2020 is also in scope for energy.
Part 3 carries the heavier question weight on ExAC Section 2 because most fire and life safety, spatial separation, and accessibility content lives there. Part 9 questions appear, but the share is smaller and tends to focus on the applicability boundary, on small residential buildings, and on common Part 9 envelope or fire-safety scenarios. Both Parts need to be tabbed; allocate study time roughly two-thirds to Part 3 and one-third to Part 9.
No, only the official NBC 2020 and NECB 2020 are permitted in the ExAC Section 2 exam room. Illustrated guides, including the NBC 2020 Part 9 Illustrated user guide, are excellent study tools at home but are not permitted references on exam day. Plan your tabbing strategy around the official code text itself, not around an illustrated guide you cannot bring.
For most Part 3 buildings, the energy code path is NECB 2020 rather than the NBC. NBC 2020 Part 3 sets fire, life safety, and structural rules; NECB 2020 sets the building envelope, lighting, and HVAC energy requirements for the same buildings. ExAC Section 2 candidates should expect Part 3 and NECB 2020 questions to appear together, because in practice a Part 3 project is designed to both at once.
NBC 2020 Part 9 includes its own energy efficiency rules in Section 9.36, which is the prescriptive energy path for housing and small buildings. Many Part 9 projects can comply through Section 9.36 alone without using NECB 2020. Provincial regulators may require an alternative path; check the provincial code (such as the OBC, ABC, or BCBC) for which energy path applies.