Spatial separation questions look like calculations, but they are really a short lookup routine. Under Subsection 3.2.3. of the NBC 2020, you find the limiting distance and the area of the exposing building face, pick one of four tables based on sprinklers and occupancy, and read the permitted percentage of unprotected openings. That percentage then sets the wall's fire-resistance rating, construction and cladding. In our experience, candidates who rehearse the routine on paper stop losing marks to it. This guide from Examitect, an independent ExAC prep platform unaffiliated with the CACB, walks through the logic and one fully worked example.
| Exam section | Section 2, about 75 multiple-choice questions in three hours, open book |
|---|---|
| Closest objectives | 5.2.2 fire safety (Part 3) and 5.3.2 safety (Part 9) |
| Part 3 rules | Division B, Subsection 3.2.3. |
| Opening tables | Tables 3.2.3.1.-B, -C, -D and -E |
| Construction table | Table 3.2.3.7. |
| Part 9 rules | Subsections 9.10.14. and 9.10.15. |
Spatial separation is the set of NBC rules that limits how much of a wall can be open, and how that wall must be built, so a fire is less likely to spread to the neighbouring building. In Part 3 it lives in Subsection 3.2.3. of Division B, and the attribution table links Article 3.2.3.1. to [F03-OP3.1], protection of adjacent buildings from fire.
The mechanism is radiant heat. Note A-3 of Division B, under "Firefighting Assumptions", says the requirements of Subsection 3.2.3. are intended to prevent fire spread from thermal radiation, assuming adequate firefighting is available. In a building that is not sprinklered, 10 to 30 minutes usually pass before radiation levels get high, and the separations are meant to hold during that window. Openings are the weak point, so the code caps their total area.
Four defined terms do the work, and Division A, Article 1.4.1.2. defines three of them:
| Term | What it means | Where |
|---|---|---|
| Exposing building face | The exterior wall facing one direction, from ground level to the ceiling of the top storey, or the wall of a fire compartment facing one direction. | Division A 1.4.1.2. |
| Limiting distance | The distance, at right angles, from the face to a property line, the centre line of a street, lane or public thoroughfare, or an imaginary line between two buildings or fire compartments on the same property. | Division A 1.4.1.2. |
| Unprotected opening | A doorway, window or opening without a closure of the required fire-protection rating, or any part of the wall with a lower fire-resistance rating than the face requires. | Division A 1.4.1.2. |
| Area of exposing building face | The wall facing one direction, from finished ground level to the uppermost ceiling, or per fire compartment behind 45 min fire separations. | Division B 3.2.3.2. |
Note A-3.2.3. explains why the code measures to the property line rather than to the building next door: otherwise the design of one property would control the design of its neighbour.
Sentence 3.2.3.1.(1) is the router. It sends you to one of four tables based on two questions: is the building or fire compartment sprinklered, and what is the occupancy group? Sentence (2) says the table value is the aggregate area of unprotected openings as a percentage of the exposing building face.
| Table | Sprinklered? | Occupancies | Rows |
|---|---|---|---|
| 3.2.3.1.-B | Not sprinklered throughout | Groups A, C, D and F, Division 3 | Face area and L/H ratio |
| 3.2.3.1.-C | Not sprinklered throughout | Groups E and F, Divisions 1 and 2 | Face area and L/H ratio |
| 3.2.3.1.-D | Sprinklered throughout | Groups A, B, C, D and F, Division 3 | Face area only |
| 3.2.3.1.-E | Sprinklered throughout | Groups E and F, Divisions 1 and 2 | Face area only |
Each table lists limiting distance across the top and the maximum face area down the side. Tables -B and -C add a length-to-height ratio in three bands (less than 3:1, 3:1 to 10:1, over 10:1), and their Note (1) says to apply L/H or H/L, whichever is greater.
The NBC gives sprinklered buildings more openings through separate tables, not a multiplier. Note A-3 explains that sprinklers should control the fire so radiation to neighbouring buildings is minimal. Compare Group D at a face area of 150 m² (Table -B, L/H less than 3:1):
| Limiting distance | Table 3.2.3.1.-B, not sprinklered | Table 3.2.3.1.-D, sprinklered |
|---|---|---|
| 2 m | 8% | 16% |
| 4 m | 13% | 30% |
| 6 m | 22% | 52% |
Sentences (5) and (8) and the doubling in Article 3.2.3.12. only apply to buildings that are not sprinklered, so none of them stacks on the sprinklered tables.
The Part 3 tables carry no note that permits interpolation. The only spatial separation note that addresses it is for houses: the Notes to Figure A-9.10.15.4.(2)-B suggest the column for the lesser limiting distance nearest the actual one, and accept interpolation above 1.2 m. For Part 3, our advice is to read the column at or below your limiting distance and the first row that covers your face area, and to confirm any interpolated value with the authority having jurisdiction.
The second half of every problem is the wall itself. Article 3.2.3.7. sends every occupancy group to Table 3.2.3.7., which sets the minimum fire-resistance rating, construction and cladding by the maximum area of unprotected openings permitted:
| Permitted openings | Groups A, B, C, D, F-3 | Groups E, F-1, F-2 | Construction | Cladding |
|---|---|---|---|---|
| 0 to 10% | 1 h | 2 h | Noncombustible | Noncombustible |
| > 10 to 25% | 1 h | 2 h | Combustible, encapsulated mass timber or noncombustible | Noncombustible |
| > 25 to 50% | 45 min | 1 h | Combustible, encapsulated mass timber or noncombustible | Noncombustible |
| > 50 to < 100% | 45 min | 1 h | Combustible, encapsulated mass timber or noncombustible | Combustible or noncombustible |
The trap is the first column. Sentence 3.2.3.1.(3) takes the rating, construction and cladding from the area determined from the tables, and the column is headed "Maximum Area of Unprotected Openings Permitted". The band depends on what the code allows at that limiting distance, not on how much glass the architect drew.
For walls that step back, Note A-3.2.3.1.(4) sets the order: Sentence (3) first, from a plane with no part of the wall in front of it, for the construction; then Sentence (4), from a plane in front of the openings, for the percentage of openings.
Sentence 3.2.3.7.(3) waives noncombustible cladding above 10% for wall assemblies that comply with Article 3.1.5.5. or 3.1.5.6. Sentence (4) adds waivers for the > 25 to 50% band built around a limiting distance greater than 5 m, full sprinklering and specific cladding types.
Illustrative example. The building, dimensions and openings below are our own numbers, not an exam question. The table values are read from the NBC 2020.
A two-storey office building (Group D) has a building area of 900 m² and is sprinklered throughout in conformance with Section 3.2. Its east wall is 20 m long, 4.5 m from the side property line, and the second-storey ceiling is 7.0 m above finished ground. The wall has twelve 1.8 m by 1.5 m windows and one 1.0 m by 2.1 m glazed exit door, none with rated closures.
Part 9 is limited to buildings of 3 storeys or less with a building area not over 600 m² (Division A, Article 1.3.3.3.). At 900 m², this building is Part 3, and offices are Group D.
Measure at right angles from the face to the property line, street centre line or imaginary line between buildings: 4.5 m.
Take the wall facing one direction from finished ground to the uppermost ceiling (Article 3.2.3.2.): 20 m x 7.0 m = 140 m².
Use Sentence 3.2.3.1.(1): sprinklered throughout and Group D points to Table 3.2.3.1.-D.
Take the first row that covers the face area and the column at or below the limiting distance: 140 m² falls in the "150 or more" row, and 4.5 m reads as the 4 m column. The value is 30%.
Sentences 3.2.3.1.(5) and (8) and Article 3.2.3.12. apply only to buildings that are not sprinklered, so none changes the 30%. Permitted openings are 30% of 140 m² = 42.0 m².
Actual openings are 12 x 2.70 m² + 2.10 m² = 34.5 m², or 24.6%, which is within 30%. Table 3.2.3.7. for 30% permitted (the > 25 to 50% band) requires a 45 min rating, any listed construction type and noncombustible cladding.
Check the lookups in your own copy:
| Lookup | Row | Column | Value |
|---|---|---|---|
| Table 3.2.3.1.-D (p. 3-85) | 150 or more m² | 4 m | 30% |
| Table 3.2.3.7. (p. 3-87) | Group D, > 25 to 50% | All columns | 45 min; combustible, encapsulated mass timber or noncombustible; noncombustible cladding |
| Table 3.2.3.1.-B (p. 3-82), comparison | 150 m², less than 3:1 | 4 m | 13% |
Conclusion: the east wall complies, with 7.5 m² to spare. Two traps sit in the last step. Reading the band from the actual 24.6% would wrongly give > 10 to 25% and 1 h. And the Sentence 3.2.3.7.(4) waivers need a limiting distance greater than 5 m, so noncombustible cladding stays unless the assembly complies with Article 3.1.5.5. or 3.1.5.6.
Without sprinklers, the route is Table 3.2.3.1.-B. L/H is 20 / 7.0 = 2.9, so the row is 150 m², less than 3:1, and the 4 m column gives 13%, or 18.2 m². The design fails, and the > 10 to 25% band lifts the rating to 1 h. With a slow fire department response, Sentence (8) halves the limiting distance to 2.25 m, read as 2.0 m: 8%, or 11.2 m². A wall that cannot meet the numbers needs a redesign or an NBC alternative solution.
Part 9 buildings follow Subsection 9.10.14. in Volume 2. Houses, and buildings with only dwelling units and none above another, follow Subsection 9.10.15., which works in glazed openings. Our post on NBC 2020 Part 3 versus Part 9 explains how to tell which Part governs.
Sentence 9.10.14.4.(1) gives three ways to set the maximum aggregate area of unprotected openings:
In Part 9 the sprinkler effect is a multiplier. Sentence 9.10.14.4.(7) allows up to twice the area where the building is sprinklered, including every adjacent room with unprotected openings, closets and bathrooms too. Sentence (6) doubles it for wired glass in steel frames or glass blocks.
Run our wall as if it were a smaller Part 9 office. Table 9.10.14.4.-A, "Over 100" row, 4.0 m column, gives 12%, or 16.8 m². The LD² route gives 4.5² = 20.25 m², so it wins. Sprinklered, that doubles to 40.5 m². Construction comes from Table 9.10.14.5.-A, with the same bands and ratings as Table 3.2.3.7. The objective 5.3 study notes cover the rest of Section 9.10.
Section 2 is the only open-book section. The 2026 Preparation Guide (p.12) allows paper copies of the NBC 2020, without provincial adaptations, and the NECB 2020, with handwritten annotations, highlighting, circling, underlining and tabs made beforehand. You may not add pages or make any mark in the room. Page 11 permits a basic calculator in every section. The page numbers below come from the NBC 2020 as published by the NRC; check them against your own printing.
| Tab | What it answers | Where |
|---|---|---|
| Definitions, Article 1.4.1.2. | Exposing building face, limiting distance, unprotected opening | Volume 1, Division A, pp. 1-7, 1-9 and 1-13 |
| Article 3.2.3.1. | Table choice and the modifiers; Table 3.2.3.1.-A follows on p. 3-79 | Volume 1, Division B, p. 3-78 |
| Tables 3.2.3.1.-B and -C | Openings, not sprinklered | Volume 1, Division B, pp. 3-81 to 3-84 |
| Tables 3.2.3.1.-D and -E, Article 3.2.3.2. | Openings, sprinklered; face area | Volume 1, Division B, p. 3-85 |
| Table 3.2.3.7. | Rating, construction and cladding | Volume 1, Division B, p. 3-87 |
| Subsection 9.10.14. | Part 9 openings (Table 9.10.14.4.-A on p. 9-65) and construction (Table 9.10.14.5.-A on p. 9-67) | Volume 2, Division B, p. 9-64 |
Name the Division on every tab, since each Division restarts its page numbers. Notes A-3.2.3. and A-3.2.3.1.(4) start on p. 3-236 if a question turns on intent or on stepped walls. The free NBC tabs sample shows a labelled set.
These questions take longer than definition questions, so bank the fast items first; our post on Section 2 pacing explains why. Rehearse the seven steps on two or three walls and the routine becomes reliable marks. The NBC 2020 reference guide covers the rest of the code.
Spatial separation is the set of NBC 2020 rules in Subsection 3.2.3. of Division B, and Subsections 9.10.14. and 9.10.15. for Part 9, that limit unprotected openings and set the construction of exterior walls based on their distance from a property line. Note A-3 says the Part 3 rules are intended to prevent fire spread from thermal radiation.
Limiting distance is the distance from an exposing building face to a property line, the centre line of a street, lane or public thoroughfare, or an imaginary line between two buildings or fire compartments on the same property, measured at right angles to the face. It is defined in Article 1.4.1.2. of Division A.
Article 3.2.3.2. of Division B takes the total area of the exterior wall facing one direction, measured from finished ground level to the uppermost ceiling. Where fire separations rated at least 45 min divide the building into fire compartments, the area may be calculated for each fire compartment.
Sentence 3.2.3.1.(1) chooses the table. Tables 3.2.3.1.-B and -C apply where the building or fire compartment is not sprinklered, and Tables -D and -E where it is. Tables -B and -D cover Groups A, C, D and F-3 (-D adds Group B), and -C and -E cover Groups E, F-1 and F-2.
Yes, sprinklering increases the permitted area. In Part 3, sprinklered buildings use Tables 3.2.3.1.-D and -E, which allow more openings; for a 150 m² Group D face at 4 m, the value rises from 13% to 30%. In Part 9, Sentence 9.10.14.4.(7) allows up to twice the area where the building is sprinklered.
The NBC 2020 Part 3 tables carry no note that permits interpolation. The only spatial separation interpolation note is for houses, in the Notes to Figure A-9.10.15.4.(2)-B. For Part 3, read the column at or below the actual limiting distance and confirm any interpolated value with the authority having jurisdiction.
The fire-resistance rating is based on the permitted openings. Table 3.2.3.7. is keyed to the maximum area of unprotected openings permitted, as determined from Tables 3.2.3.1.-B to -E under Sentence 3.2.3.1.(3), not to the area of glazing actually designed.
Part 9 uses Subsection 9.10.14., or Subsection 9.10.15. for houses. Sentence 9.10.14.4.(1) allows Table 9.10.14.4.-A, the Part 3 method, or the limiting distance squared, halved for mercantile and medium-hazard industrial occupancies. Table 9.10.14.5.-A then sets the construction of the exposing building face.