Small Buildings (NBC 2020)

Topic overview: three sub-categories

Examitect's ExAC study plan organises Small Buildings into three sub-categories. Click a row to jump directly to that section of the notes.

What Part 9 is and who it applies to

Part 9 of Division B of the NBC 2020 is the prescriptive chapter for small buildings. It gives you a set of minimum requirements: if you follow them, you comply with the code without calculations, engineering analysis, or alternative solution submissions.

Article 1.3.3.3 of Division A sets the three thresholds that must all be met:

1. Building height: 3 storeys or less above grade.
2. Building area: 600 m² or less (the footprint of the building at grade, not the sum of all floor areas).
3. Major occupancy: one or more of Groups B Division 4, C, D, E, or F Divisions 2 and 3.

If a building exceeds any one of these thresholds, or if it contains an occupancy in Groups A, B Divisions 1, 2 or 3, or F Division 1, Part 3 applies instead. Part 9 and Part 3 can coexist in the same building only through a specific conditional framework set out in Division A; otherwise the more demanding Part governs the entire building.

5.16 Apply prescriptive requirements of Part 9 buildings

Sub-category 5.16 tests whether you can identify when Part 9 applies and navigate its prescriptive structure. The starting point is always Article 1.3.3.3 of Division A.

Occupancy groups and Part 9 eligibility

What Part 9 prescribes

Part 9 covers foundations (9.4, 9.15 to 9.16), wood framing (9.23), masonry (9.20), concrete (9.21), fire protection and occupant safety (9.10), windows and doors (9.7), means of egress (9.9), plumbing rough-in (9.31 to 9.33), and building envelope (9.25 to 9.27, 9.36). Each section provides prescriptive minimum requirements without requiring engineering design.

Section 9.10 at a glance

Section 9.10 is the most tested section under sub-category 5.16. It covers fire-resistance requirements for separations between suites, corridors, exits, garages, and service rooms; smoke alarm placement and interconnection; flame spread ratings for interior finishes; spatial separation from property lines; and fire blocking in concealed spaces. The numerical values from this section appear in nearly every exam session for Small Buildings.

5.17 Apply Part 9 requirements for safety and health

Sub-category 5.17 focuses on the occupant-facing safety provisions: windows, doors, and skylights (Section 9.7); means of egress (Section 9.9); fire protection and occupant safety (Section 9.10); and plumbing, ventilation, and heating (Sections 9.31 to 9.33).

Section 9.7: windows, doors, and skylights

Windows and exterior doors must achieve an airtightness classification of A2, with an air leakage rate of no more than 1.5 L/(s·m²) at 75 Pa. For security, an exterior door must be of solid wood construction at least 45 mm thick or equivalent. Deadbolt locks must have a 5-pin tumbler cylinder, a bolt throw of at least 25 mm, and a guard bolt of at least 15 mm.

Section 9.9: means of egress dimensions

Bedroom emergency egress windows

Every bedroom must have at least one window that can serve as an emergency escape opening. All three conditions must be met at the same time:

• Unobstructed openable area of at least 0.35 m²
• No dimension less than 380 mm
• Finished sill height no more than 1 m above the finished floor

A bedroom window on an upper floor must also be within 7 m of finished grade, or a rescue path must be provided. All three dimensions are tested together in scenario questions. Two out of three correct is still a wrong answer.

Sections 9.31 to 9.33: plumbing, ventilation, and heating

These sections set minimum standards for rough-in plumbing, whole-house ventilation rates, and heating system performance. They appear less often in exam questions than Sections 9.7, 9.9, and 9.10, but you should know that minimum fresh-air ventilation for a dwelling unit is defined in Section 9.32 and is tied to the number of occupants.

Section 9.10: fire-resistance, smoke alarms, and interior finishes

Section 9.10 is the most number-dense section in Part 9. Expect at least two or three questions per exam session that require you to recall a specific fire-resistance rating, smoke alarm placement rule, or flame spread limit.

Fire-resistance ratings for common assemblies

Sound transmission class

Floor and wall assemblies separating dwelling units in the same building must achieve an STC of at least 50. The STC requirement between a secondary suite and the main dwelling is 43.

Smoke alarms

At least one smoke alarm must be installed on every storey of a dwelling unit, including the basement. At least one must be installed in each sleeping room. Where more than one smoke alarm is installed in a dwelling unit, all alarms must be interconnected so that activating any one alarm sounds all others.

Flame spread ratings for interior finishes

Spatial separation and fire blocking

An unprotected opening in an exposing building face requires a limiting distance of at least 1.2 m from the property line (or mid-point of a lane). Fire blocks are required in concealed wall and floor spaces where a concealed air space is more than 25 mm deep, at vertical intervals of no more than 3 m and horizontal intervals of no more than 20 m. Acceptable fire-block materials include sheet steel at least 0.38 mm thick, gypsum board at least 12.7 mm thick, or plywood at least 12.5 mm thick.

5.18 Apply Part 9 building envelope and energy provisions

Sub-category 5.18 covers how you build the thermal envelope of a small building: insulation placement, air barrier and vapour barrier requirements (Section 9.25), roofing (Section 9.26), cladding (Section 9.27), and energy compliance paths (Section 9.36).

Section 9.25: insulation installation rules

Insulation must be in full contact with the surface it is protecting without compression. Loose-fill insulation in unconfined sloped roof spaces is limited to a maximum slope of 4.5:12 for mineral fibre or cellulose, or 2.5:12 for other types.

Section 9.25: air barrier system

An air barrier conforming to CAN/CGSB-51.34-M (polyethylene sheeting) must be installed. At joints, the barrier must be lapped at least 100 mm and mechanically clamped or sealed. The air barrier is the continuity layer that controls air movement through the assembly; it is a distinct requirement from the vapour barrier.

Section 9.25: vapour barrier

The vapour barrier must have a permeability of no more than 60 ng/(Pa·s·m²), be placed on the warm side of the insulation (the interior side in a cold climate), and be at least 0.15 mm thick polyethylene. Under a floor-on-ground slab, a polyethylene sheet of at least 0.15 mm must be installed with joints lapped at least 300 mm.

Sections 9.26, 9.27, and 9.36: roofing, cladding, and energy

Section 9.26: roofing

For asphalt shingles, Section 9.26 requires at least 4 fasteners per shingle and a minimum head lap of 50 mm. Valley flashings must be at least 600 mm wide (300 mm each side of the valley centre line). Eave protection must extend at least 900 mm up the slope from the eave and at least 300 mm inside the inside face of the exterior wall. Counter flashings at masonry must be set at least 25 mm into the masonry, extend at least 150 mm down the masonry face, and lap the base flashing by at least 100 mm. Weep holes must be spaced at no more than 800 mm on centre.

Section 9.27: cladding

Section 9.27 sets out minimum requirements for wood siding, stucco, brick veneer, and other cladding types. Cladding must be separated from the air barrier by a drainage space or drainage mat where moisture is likely to accumulate. Fastener patterns and clearances depend on the cladding type and substrate.

Section 9.36: energy efficiency compliance paths

For the exam, focus on the prescriptive path. RSI values (the metric equivalent of imperial R-values) are specified by climate zone for walls, attics, floors, foundations, and windows. One RSI point equals approximately 5.68 imperial R.

Which reference to use for each sub-category

The ExAC is open-book. Knowing which tab to flip to, rather than memorising every number, is how you use your time efficiently. That said, the FRR values from Section 9.10, the egress dimensions from Section 9.9, and the bedroom window numbers are worth memorising because they appear in quick-answer questions where table-flipping costs you too much time.

Key terms for Small Buildings

Building area

The greatest horizontal area of a building above grade within the outside surface of exterior walls, or within the outside surface of exterior walls and the centre line of firewalls. The Part 9 threshold (600 m²) is measured against this, not against total floor area.

Building height

The number of storeys contained between the roof and the floor of the first storey above grade. The Part 9 threshold is 3 storeys.

Major occupancy

The principal occupancy for which a building or part of a building is used or intended to be used. Determines which Division of Part 9 (or Part 3) applies.

Fire-resistance rating (FRR)

The time in hours or minutes that an assembly maintains its load-bearing capacity, integrity, or thermal resistance under standardised fire conditions (CAN/ULC-S101). Section 9.10 specifies FRRs for Part 9 buildings.

Sound transmission class (STC)

A single-number rating of a wall or floor assembly's ability to attenuate airborne sound. Section 9.10 requires STC 50 between dwelling units and STC 43 at secondary suites.

Air barrier system

A continuous, durable material or assembly of materials (conforming to CAN/CGSB-51.34-M) that controls air movement between conditioned and unconditioned spaces. It is placed at the building enclosure and is a separate requirement from the vapour barrier.

Vapour barrier

A material with a water vapour permeance of no more than 60 ng/(Pa·s·m²), placed on the warm side of insulation to retard vapour diffusion into the assembly. Minimum thickness is 0.15 mm polyethylene.

RSI value

The metric thermal resistance of an insulation or assembly. RSI 1.0 equals approximately imperial R-5.68. Section 9.36 specifies minimum RSI values by climate zone for walls, attics, floors, foundations, and windows.

Exposing building face

An exterior wall or portion of an exterior wall that faces a property line, street, or public space. Spatial separation rules in Section 9.10 limit unprotected openings based on the limiting distance.

Limiting distance

The distance from an exposing building face to the closer of the property line, the centre line of a street, or an imaginary line between the building and a facing building on the same lot. Controls the amount of unprotected opening area permitted in the exposing building face.

Fire separation

A construction assembly (wall, floor, or ceiling) that separates two spaces within a building and limits the spread of fire and smoke. A fire separation may or may not have a fire-resistance rating.

Travel distance

The distance a person must walk from any point in a floor area to the nearest exit. Section 9.9 limits this to 40 m for unsprinklered Part 9 buildings or 45 m where sprinklers are provided.

Deadbolt

A bolt that is moved by rotating a knob or key, rather than spring-loaded. Section 9.7 requires a minimum 5-pin tumbler cylinder, a bolt throw of 25 mm, and a guard bolt of 15 mm.

Eave protection

A water-resistant underlayment applied at the eave to prevent water from ice damming from entering the building. Section 9.26 requires it to extend 900 mm up slope from the eave and 300 mm inside the exterior wall face.

Prescriptive compliance

Meeting code requirements by following specified minimum values or methods directly, without calculations or performance modelling. Contrasts with alternative solutions, which require a demonstration of equivalent performance.

Means of egress

A continuous path of travel from any point in a building to a public thoroughfare. Includes exit access (corridors), exits (stairs, doors), and exit discharge (paths to grade).

Secondary suite

A self-contained dwelling unit within or attached to a house. Part 9 provisions for secondary suites are less stringent than for multi-unit buildings in some respects (e.g., STC 43 rather than 50).

Dead-end corridor

A corridor that is open at one end only, requiring an occupant to retrace their steps to reach an exit. Section 9.9 limits dead-end corridors to 6 m in length.

Question patterns for Small Buildings

Small Buildings questions follow consistent patterns. Knowing the format helps you allocate time and identify what the question is really testing.

Six common traps in Small Buildings questions

1. Using Part 3 FRRs in a Part 9 building. Part 3 and Part 9 have different fire-resistance rating requirements for the same assembly type. If the question describes a Part 9 building, the answer comes from Section 9.10, not from Part 3, Sections 3.2 or 3.3. Switching Parts is the most common error.
2. Confusing building area with floor area. The 600 m² Part 9 threshold is the horizontal footprint of the building, not the sum of all floor areas. A 2-storey house can have 700 m² of total floor area and still qualify for Part 9 if its footprint is 350 m².
3. Including a disqualifying occupancy. A building with any Group A or Group B Division 1, 2, or 3 occupancy does not qualify for Part 9, regardless of height or area. Watch for a small day care (Group B Div 2 or 3) embedded in what otherwise looks like a residential building.
4. Getting the garage FRR wrong. The rating depends on car count (5 or fewer = 1 h; more than 5 = 1.5 h) and purpose (repair garage = 2 h). Questions often describe a garage with 6 cars to test whether you apply the correct threshold.
5. Reversing the vapour barrier and air barrier. The vapour barrier goes on the warm side (interior in a cold climate). The air barrier is a separate, continuous plane of airtightness. Placing the vapour barrier on the exterior, or treating the two as the same layer, costs marks on 5.18 questions.
6. Missing one of the three bedroom window conditions. An emergency egress window must meet all three requirements at once: at least 0.35 m² of openable area, no dimension less than 380 mm, and a sill height no more than 1 m above the finished floor. A window that satisfies two of the three fails the question.

Study tips for Small Buildings

1. Start with Article 1.3.3.3. Read the application article before anything else. Every eligibility question hinges on the three thresholds. Know them before touching Sections 9.7 through 9.36.
2. Memorise the Section 9.10 FRR table. The eight FRR values for garages, suites, corridors, and service rooms are tested repeatedly. Write them from memory until they are automatic.
3. Know all three bedroom window numbers. 0.35 m², 380 mm, 1 m. All three must appear in your answer at once.
4. Use NBC Part-9 Illustrated for Section 9.25. The diagrams show air barrier lapping, vapour barrier placement, and eave protection in a single image. Seeing the assembly visually is faster than parsing code text.
5. Treat Section 9.36 as a decision tree. Learn the four paths and when a builder would choose each. Most exam questions ask you to pick the right path, not perform the calculation.
6. Practice distinguishing building area from floor area. Sketch a multi-storey building and label both values. The habit of separating them takes only a few practice problems to develop.
7. Connect Section 9.9 to Section 9.10. Exit corridors must meet both egress dimensions (Section 9.9) and fire-resistance ratings (Section 9.10). Questions that describe a corridor scenario often test both sections in a single question.

A suggested 12 to 18 hour study plan

1. Hours 1 to 2: Read Article 1.3.3.3 and all of Section 9.10 in the NBC.
2. Hours 3 to 4: Read Sections 9.7 and 9.9; note all dimensions and ratings.
3. Hours 5 to 6: Work through NBC Part-9 Illustrated for Sections 9.7, 9.9, 9.10, and 9.25.
4. Hours 7 to 9: Read Sections 9.25, 9.26, and 9.27; sketch the wall assembly from memory and label each layer.
5. Hours 10 to 11: Read Section 9.36; write out the four compliance paths in your own words.
6. Hours 12 to 14: Drill Examitect practice questions across all three sub-categories.
7. Hours 15 to 18: Review wrong answers; re-read the relevant NBC sections for each error.