SB-2 fire-resistance rating calculations

Last updated October 22, 2026

When this shows up on the exam

Part 9 lets you prove a fire-resistance rating three ways: a test, SB-2 "Fire Performance Ratings", or the SB-3 tables (OBC Div. B 9.10.3.1.). The House and Small Buildings exams use SB-2 for two kinds of calculation:

Masonry and concrete: turn a hollow unit into an equivalent thickness, add credit for plaster or gypsum board, then read the rating from a thickness table.
Framed assemblies: add up the minutes SB-2 assigns to the membrane, the framing and any insulation (the component additive method).

Expect a stem that describes an assembly and asks for the rating, or asks what thickness or extra layer is needed to reach a target.

The method

A. Masonry and concrete walls

Find the equivalent thickness. For a hollow unit, multiply the actual overall thickness by net volume divided by gross volume, in other words the percent solid (SB-2 1.6.1.(3)). Gross volume uses the actual length, height and thickness, not nominal sizes (SB-2 1.6.1.(5)). Solid units use their actual thickness.
Add finishes. Multiply the actual plaster or gypsum board thickness by the factor in SB-2 Table 1.7.1., choosing the column for the masonry or concrete type (SB-2 1.7.1.(1)).
Exception: gypsum board, or gypsum lath and plaster, on the fire-exposed side is not converted to millimetres. It earns minutes from Tables 2.3.4.A. to 2.3.4.D. instead (SB-2 1.7.1.(5)).
Read SB-2 Table 2.1.1.. Pick the row for the wall type and concrete type (S, N, L, L₁, L₂ and the sand-blend types). Then move right to the last column whose thickness your wall still meets.
Check the two caps. The whole assembly may not exceed twice the rating of the bare masonry or concrete (SB-2 1.7.1.(2)). A finish on the non-fire-exposed side may add no more than half of what the bare wall provides (SB-2 1.7.1.(4)).

The table gives values at fixed ratings. SB-2's own sample calculations interpolate between columns when they need a time in minutes. When a question asks for a tabulated rating, do not round your thickness up into the next column.

B. Wood and steel framed assemblies (component additive)

Membrane on the fire-exposed side: minutes from SB-2 Table 2.3.4.A. for walls, Table 2.3.4.B. for floors, Table 2.3.4.C. for roofs. Walls have separate loadbearing and non-loadbearing columns.
Framing: SB-2 Table 2.3.4.E. for studs (spacing matters), Table 2.3.4.F. for joists and trusses.
Extras: insulation or a concrete topping from SB-2 Table 2.3.4.G.. Read its notes; some credits apply to wood framing only.
The membrane on the non-fire-exposed side adds nothing (SB-2 2.3.5.(1)).
Loadbearing wall with a single layer of gypsum board on resilient metal channels: subtract 10 min (SB-2 2.3.4.(1)).
Cap the result at 90 min (SB-2 2.3.1.(1)). Extra layers earn nothing unless the table lists that layered membrane (SB-2 2.3.3.(3)).

Worked example 1: hollow concrete block

A wall of hollow concrete blocks, 190 mm actual thickness, 53% solid. The coarse aggregate is limestone, so the concrete is Type N (SB-2 1.4.1.(3)). No finishes.

Step	Working	Result
Equivalent thickness	190 mm × 0.53	100.7 mm
Table row	Table 2.1.1., concrete masonry units, Type S or N
1.5 h column	95 mm needed; 100.7 ≥ 95	meets
2 h column	113 mm needed; 100.7 < 113	fails

Tabulated rating: 1.5 h (SB-2 Table 2.1.1.). Using the 190 mm actual thickness instead would wrongly reach the 4 h column.

Worked example 2: adding gypsum board to the block wall

Now add 12.7 mm Type X gypsum board to one face. The fire is assumed on the bare face, so the board is on the non-fire-exposed side.

Step	Working	Result
Factor	Table 1.7.1., gypsum board row, column for Type N unit masonry	1.25
Board credit	12.7 mm × 1.25	15.9 mm
Total	100.7 + 15.9	116.6 mm
Table 2.1.1.	2 h needs 113 mm; 3 h needs 142 mm	2 h
Cap, 1.7.1.(4)	board adds 30 min; limit is 0.5 × 90 min = 45 min	OK
Cap, 1.7.1.(2)	2 h ≤ 2 × 1.5 h	OK

Rating: 2 h. If the same board faced the fire, you would not use the factor. It would earn 25 min from Table 2.3.4.A., added to the masonry time, as SB-2 Example (2) shows.

Worked example 3: wood stud wall by component additive

An interior loadbearing wall: 38 × 89 mm wood studs at 406 mm o.c., one layer of 15.9 mm Type X gypsum board on each face, cavities filled with rock fibre batts of at least 1.22 kg/m².

Component	Source	Minutes
15.9 mm Type X, fire side, loadbearing	Table 2.3.4.A.	40
Wood studs ≤ 406 mm o.c.	Table 2.3.4.E.	20
Rock fibre insulation, wood studs	Table 2.3.4.G.	15
Board on the far side	2.3.5.(1)	0
Total	40 + 20 + 15	75

Rating: 75 min, under the 90 min cap (SB-2 2.3.4.). With studs at 610 mm o.c. the framing earns 15 min and the wall drops to 70 min.

Common mistakes

Using the actual or nominal unit thickness instead of the equivalent thickness.
Building gross volume from nominal sizes (400 × 200 × 200) instead of actual sizes.
Reading the wrong part of Table 2.1.1.: monolithic concrete rows instead of concrete masonry unit rows, or the wrong aggregate row.
Rounding a thickness up into the next column (111.6 mm is not 112 mm).
Picking the wrong Table 1.7.1. column, or applying the factor to gypsum board on the fire-exposed side.
Forgetting the 1.7.1.(4) half-contribution cap on a finish on the far side, or the 1.7.1.(2) double cap.
Crediting the membrane on the non-fire-exposed side.
Crediting two layers of 15.9 mm Type X on a wall: Table 2.3.4.A. lists only double 12.7 mm, so the second layer earns nothing.
Using the non-loadbearing column for a loadbearing wall (double 12.7 mm is 50 min loadbearing, 80 min non-loadbearing).
Giving glass fibre or rock fibre credit to steel studs; those Table 2.3.4.G. wall credits are for wood studs.
Forgetting the 10 min deduction for resilient channels, or the 90 min cap.

Find it fast in the code PDF

SB-2 is in the Supplementary Standards volume, not Division B. Bookmark Supplementary Standards > SB-2 Fire Performance Ratings > Section 1 (1.6 and 1.7) and Section 2 (2.1 and 2.3). Ctrl+F terms that appear in the text:

"net volume of the unit" (hollow unit rule, 1.6.1.)
"shall not exceed 0.5 times" (far-side finish cap, 1.7.1.(4))
"component additive method" (Subsection 2.3)
"Time Assigned to Protective Membranes" (Table 2.3.4.A.)
"not more than 90 min" (cap, 2.3.1.)

Drill these questions

Calculation questions in the exam format, each worked and cited. Pick your exam; sign in to start, a free account gets the free questions.

Code cited in this method

Based on the official 2024 Building Code Compendium on ontario.ca.

OBC Div. B 9.10.3.1. Fire-Resistance and Fire-Protection Ratings
(1)Where a fire-resistance rating or a fire-protection rating is required in this Section for an element of a building, such rating shall be determined in conformance with
(a)the test methods described in Part 3,
(b)MMAH Supplementary Standard SB-2, "Fire Performance Ratings," or
(c)MMAH Supplementary Standard SB-3, "Fire and Sound Resistance Tables."
Open OBC Div. B 9.10.3.1. in the code viewer
OBC SB-2 1.6.1. Method of Calculating
(1)The thickness of solid-unit masonry and concrete described in this Supplementary Standard shall be the thickness of solid material in the unit or component thickness. For units that contain cores or voids, the Tables refer to the equivalent thickness determined in conformance with Sentences (2) to (10).
(2)Where a plaster finish is used, the equivalent thickness of a wall, floor, column or beam protection shall be equal to the sum of the equivalent thicknesses of the concrete or masonry units and the plaster finish measured at the point that will give the least value of equivalent thickness.
(3)Except as provided in Sentence (5), the equivalent thickness of a hollow masonry unit shall be calculated as equal to the actual overall thickness of a unit in millimetres multiplied by a factor equal to the net volume of the unit and divided by its gross volume.
(4)Net volume shall be determined using a volume displacement method that is not influenced by the porous nature of the units.
(5)Gross volume of a masonry unit shall be equal to the actual length of the unit multiplied by the actual height of the unit multiplied by the actual thickness of the unit.
(6)Where all the core spaces in a wall of hollow concrete masonry or hollow-core precast concrete units are filled with grout, mortar, or loose fill materials such as expanded slag, burned clay or shale (rotary kiln process), vermiculite or perlite, the equivalent thickness rating of the wall shall be considered to be the same as that of a wall of solid units, or a solid wall of the same concrete type and the same overall thickness.
(7)The equivalent thickness of hollow-core concrete slabs and panels having a uniform thickness and cores of constant cross section throughout their length shall be obtained by dividing the net cross-sectional area of the slab or panel by its width.
(8)The equivalent thickness of concrete panels with tapered cross sections shall be the cross section determined at a distance of 2 t or 150 mm, whichever is less, from the point of minimum thickness, where t is the minimum thickness.
(9)Except as permitted in Sentence (10), the equivalent thickness of concrete panels with ribbed or undulating surfaces shall be
(a)t_a for s less than or equal to 2 t,
(b)t + (4t/s − 1)(t_a − t) for s less than 4 t and greater than 2 t, and
(c)t for s greater than or equal to 4 t
where
- t = minimum thickness of panel,
- t_a = average thickness of panel (unit cross-sectional area divided by unit width), and
- s = centre to centre spacing of ribs or undulations.
(10)Where the total thickness of a panel described in Sentence (9), exceeds 2 t, only that portion of the panel which is less than 2 t from the non-ribbed surface shall be considered for the purpose of the calculations in Sentence (9).
Open OBC SB-2 in the code viewer
OBC SB-2 Table 1.7.1. Type of Masonry or Concrete
Table 1.7.1. — Type of Masonry or Concrete Type of Surface Protection | Type of Masonry or Concrete: Solid Clay Brick, Unit Masonry and Monolithic Concrete, Type N or S | Type of Masonry or Concrete: Cored Clay Brick, Clay Tile, Monolithic Concrete, Type L₄0S and Unit Masonry, Type L₁20S | Type of Masonry or Concrete: Concrete Unit Masonry, Type L₁ or L₂ 20S and Monolithic Concrete, Type L | Type of Masonry or Concrete: Concrete Unit Masonry, Type L₂ Portland cement-sand plaster or lime sand plaster | 1.00 | 0.75 | 0.75 | 0.50 Gypsum-sand plaster, wood fibred gypsum plaster or gypsum board | 1.25 | 1.00 | 1.00 | 1.00 Vermiculite or perlite aggregate plaster | 1.75 | 1.50 | 1.25 | 1.25 Column 1 | 2 | 3 | 4 | 5
Open OBC SB-2 Table 1.7.1. in the code viewer
OBC SB-2 1.7.1. Determination of Contribution
(1)Except as provided in Sentences (2) to (5), the contribution of a plaster or gypsum board finish to the fire resistance of a masonry or concrete wall, floor or roof assembly shall be determined by multiplying the actual thickness of the finish by the factor shown in Table 1.7.1., depending on the type of masonry or concrete to which it is applied. This corrected thickness shall then be included in the equivalent thickness as described in Subsection 1.6.
(2)Where a plaster or gypsum board finish is applied to a concrete or masonry wall, the calculated fire-resistance rating of the assembly shall not exceed twice the fire-resistance rating provided by the masonry or concrete because structural collapse may occur before the limiting temperature is reached on the surface of the non-fire-exposed side of the assembly.
(3)Where a plaster or gypsum board finish is applied only on the non-fire-exposed side of a hollow clay tile wall, no increase in fire resistance is permitted because structural collapse may occur before the limiting temperature is reached on the surface of the non-fire-exposed side of the assembly.
(4)The contribution to fire resistance of a plaster or gypsum board finish applied to the non-fire-exposed side of a monolithic concrete or unit masonry wall shall be determined in conformance with Sentence (1), but shall not exceed 0.5 times the contribution of the concrete or masonry wall.
(5)When applied to the fire-exposed side, the contribution of a gypsum lath and plaster or gypsum board finish to the fire resistance of masonry or concrete wall, floor or roof assemblies shall be determined from Table 2.3.4.A. to 2.3.4.D.
Open OBC SB-2 in the code viewer
OBC SB-2 Table 2.1.1. Minimum Equivalent Thicknesses [1] of Unit Masonry and Monolithic Concrete Walls Loadbearing and Non-Loadbearing, mm
Table 2.1.1. — Minimum Equivalent Thicknesses [1] of Unit Masonry and Monolithic Concrete Walls Loadbearing and Non-Loadbearing, mm Type of Wall | Fire-Resistance Rating: 30 min | Fire-Resistance Rating: 45 min | Fire-Resistance Rating: 1 h | Fire-Resistance Rating: 1.5 h | Fire-Resistance Rating: 2 h | Fire-Resistance Rating: 3 h | Fire-Resistance Rating: 4 h Solid brick units (80% solid and over), actual overall thickness | 63 | 76 | 90 | 108 | 128 | 152 | 178 Cored brick units and hollow tile units (less than 80% solid), equivalent thickness | 50 | 60 | 72 | 86 | 102 | 122 | 142 Column 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 Table 2.1.1. (Continued) — Solid and hollow concrete masonry units, equivalent thickness Type of Wall | Fire-Resistance Rating: 30 min | Fire-Resistance Rating: 45 min | Fire-Resistance Rating: 1 h | Fire-Resistance Rating: 1.5 h | Fire-Resistance Rating: 2 h | Fire-Resistance Rating: 3 h | Fire-Resistance Rating: 4 h Type S or N concrete[2] | 44 | 59 | 73 | 95 | 113 | 142 | 167 Type L₁20 S concrete | 42 | 54 | 66 | 87 | 102 | 129 | 152 Type L₁ concrete | 42 | 54 | 64 | 82 | 97 | 122 | 143 Type L₂20 S concrete | 42 | 54 | 64 | 81 | 94 | 116 | 134 Type L₂ concrete | 42 | 54 | 63 | 79 | 91 | 111 | 127 Column 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 Table 2.1.1. (Continued) — Monolithic concrete and concrete panels, equivalent thickness Type of Wall | Fire-Resistance Rating: 30 min | Fire-Resistance Rating: 45 min | Fire-Resistance Rating: 1 h | Fire-Resistance Rating: 1.5 h | Fire-Resistance Rating: 2 h | Fire-Resistance Rating: 3 h | Fire-Resistance Rating: 4 h Type S concrete | 60 | 77 | 90 | 112 | 130 | 158 | 180 Type N concrete | 59 | 74 | 87 | 108 | 124 | 150 | 171 Type L40 S or Type L concrete | 49 | 62 | 72 | 89 | 103 | 124 | 140 Column 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 Notes to Table 2.1.1.: (1) See definition of equivalent thickness in Subsection 1.6. (2) Hollow concrete masonry units made with Type S or N concrete shall have a minimum compressive strength of 15 MPa based on net area, as defined in CSA A165.1, "Concrete block masonry units".
Open OBC SB-2 Table 2.1.1. in the code viewer
OBC SB-2 Table 2.3.4.A. Time Assigned to Protective Membranes on Fire-Exposed Side of Wood-Framed and Cold-Formed-Steel-Framed Walls
Table 2.3.4.A. Time Assigned to Protective Membranes on Fire-Exposed Side of Wood-Framed and Cold-Formed-Steel-Framed Walls Description of Finish | Time — Loadbearing Walls, min | Time — Non-Loadbearing Walls, min 11.0 mm Douglas Fir plywood phenolic bonded | N/A | 10[1] 14.0 mm Douglas Fir plywood phenolic bonded | N/A | 15[1] 12.7 mm Type X gypsum board | 25[2] | 25 15.9 mm Type X gypsum board | 40[2] | 40[3] Double 12.7 mm Type X gypsum board[4] | 50 | 80 Column 1 | 2 | 3 Notes to Table 2.3.4.A.: (1) Applies to stud cavities filled with mineral wool conforming to CAN/ULC-S702.1, "Standard for Mineral Fibre Thermal Insulation for Buildings, Part 1: Material Specification", and having a mass per unit area of not less than 2 kg/m², with no additional credit for insulation according to Table 2.3.4.G. (2) Applies only to wood-framed walls. (3) Applies only to steel-framed walls. (4) Resilient metal channels are permitted to be installed at a spacing of 406 mm o.c. with no effect on the rating of the wall assembly.
Open OBC SB-2 Table 2.3.4.A. in the code viewer
OBC SB-2 Table 2.3.4.E. Time Assigned for Contribution of Wood-Framed or Cold-Formed-Steel-Framed Walls
Table 2.3.4.E. Time Assigned for Contribution of Wood-Framed or Cold-Formed-Steel-Framed Walls Description of Frame | Time — Loadbearing Walls, min | Time — Non-Loadbearing Walls, min Wood studs spaced ≤ 406 mm o.c. | 20 | 20 Wood studs spaced ≤ 610 mm o.c. | 15 | 15 Cold-formed-steel studs spaced ≤ 406 mm o.c. | 10 | 10 Cold-formed-steel studs spaced ≤ 610 mm o.c. | 10 | N/A Column 1 | 2 | 3
Open OBC SB-2 Table 2.3.4.E. in the code viewer
OBC SB-2 Table 2.3.4.G. Time Assigned for Additional Protection
Table 2.3.4.G. Time Assigned for Additional Protection Description of Additional Protection | Time, min Add to the fire-resistance rating of wood stud walls, sheathed with gypsum board or lath and plaster, if the spaces between the studs are filled with preformed insulation of rock or slag fibres conforming to CAN/ULC-S702.1, "Standard for Mineral Fibre Thermal Insulation for Buildings, Part 1: Material Specification", and with a mass per unit area of not less than 1.22 kg/m² of wall surface | 15[1] Add to the fire-resistance rating of non-loadbearing wood stud walls, sheathed with gypsum board or lath and plaster, if the spaces between the studs are filled with preformed insulation of glass fibres conforming to CAN/ULC-S702.1, "Standard for Mineral Fibre Thermal Insulation for Buildings, Part 1: Material Specification", and having a mass per unit area of not less than 0.6 kg/m² of wall surface | 5[2] Add to the fire-resistance rating of loadbearing wood stud walls, sheathed with gypsum board if the spaces between the studs are filled with of cellulose fibres conforming to CAN/ULC-S703, "Standard for Cellulose Fibre Insulation for Buildings", and having a density of not less than 50 kg/m³ | 10 Add to the fire-resistance rating of plaster on gypsum lath ceilings if 0.76 mm diam wire mesh with 25 mm by 25 mm openings or 1.57 mm diam diagonal wire reinforcing at 250 mm o.c. is placed between lath and plaster | 30 Add to the fire-resistance rating of plaster on gypsum lath ceilings if 76 mm wide metal lath strips are placed over joints between lath and plaster | 10 Add to the fire-resistance rating of plaster on 9.5 mm thick gypsum lath ceilings (Table 2.3.4.D.) if supports for lath are 305 mm o.c. | 10 Add to the fire-resistance rating of floor assemblies if the spaces between the structural member are filled with preformed insulation of rock or slag fibres conforming to CAN/ULC-S702.1, "Standard for Mineral Fibre Thermal Insulation for Buildings, Part 1: Material Specification", and having a mass per unit area of not less than 1.22 kg/m² of floor surface | 5[2] Add to the fire-resistance rating of floor assemblies if the spaces between the structural members studs are filled with wet-blown cellulose fibres conforming to CAN/ULC-S703, "Standard for Cellulose Fibre Insulation for Buildings", and having a density of not less than 50 kg/m³ | 5[2][3] Add to the fire-resistance rating of floor assemblies where the floor topping on the unexposed side of the floor assemblies consists of concrete not less than 38 mm thick | 5[2] Column 1 | 2 Notes to Table 2.3.4.G.: (1) Applies to wood-framed walls only. (2) Applies to wood joists, wood trusses, wood I-joists and cold-formed-steel joists (C-shaped joists). (3) Applies to cellulose fibre: (i) for wood joists, wood I-joist and wood trusses that is sprayed-applied with a minimum density of 50 kg/m³, a minimum depth of 90 mm on the underside of the subfloor, and of 90 mm on the sides of the structural members. (ii) for cold-formed-steel joists that is spray-applied with a minimum density of 50 kg/m³ and a minimum thickness of 90 mm on the underside of the subfloor, of 90 mm on the sides of the structural members, and of 13 mm on the underside of the bottom flange other than at resilient metal channel locations.
Open OBC SB-2 Table 2.3.4.G. in the code viewer

Show all 13 articles

OBC SB-2 2.3.5. Considerations for Various Types of Assemblies
(1)Interior vertical fire separations are to be rated for exposure to fire on each side (See Sentence 3.1.3.7.(2) of Division B of the 2024 Building Code). The method described in this Subsection applies when a membrane is provided on both sides of the assembly. However, in the calculation of the fire-resistance rating of such an assembly using this method, no additional contribution to fire-resistance is to be assigned for a membrane on the non-fire-exposed side, since its contribution is already accounted for in the values assigned to the other components of the assembly.
(2)Exterior wall assemblies required to have a fire-resistance rating are required to be rated for exposure to fire from the interior side only (See Sentence 3.1.3.7.(3) of Division B of the 2024 Building Code). When deriving a fire-resistance rating for such wall assemblies using the method described in this Subsection, only wood studs with a single layer of gypsum board or non-loadbearing cold-formed-steel studs conforming to Table 2.3.4.E. may be used. Such walls must have a membrane on the exterior side of the stud consisting of plywood, oriented strandboard or gypsum sheathing and exterior cladding. Additional materials are also permitted between the required sheathing and cladding. The spaces between the studs are to be filled with insulation conforming to CAN/ULC-S702.1, "Standard for Mineral Fibre Thermal Insulation for Buildings, Part 1: Material Specification", and having a mass per unit area of not less than 1.22 kg/m² of wall surface. However, in the calculation of the fire-resistance rating of such an assembly, no additional contribution to fire resistance is to be assigned for a membrane on the non-fire-exposed side, since its contribution is already accounted for in the values assigned to the other components of the assembly.
(3)In the case of a floor or roof assembly, the Building Code only requires testing for fire exposure from below. Floors or roofs must have an upper flooring or roofing membrane in accordance with Table 2.3.5.
(4)Insulation used in the cavities of a wood joist or metal-plate-connected wood truss floor assembly with a single layer of gypsum board will not reduce the assigned fire-resistance rating of the assembly provided:
(a)the insulation is preformed of rock, slag or glass fibre conforming to CAN/ULC-S702.1, "Standard for Mineral Fibre Thermal Insulation for Buildings, Part 1: Material Specification", and having a mass per unit area of not more than 1.1 kg/m² and is installed adjacent to the bottom edge of the framing member, directly above steel furring channels,
(b)the gypsum board ceiling membrane is attached to
(i)wood trusses in conformance with Sentence 2.3.9.(2) by way of steel furring channels spaced not more than 406 mm o.c., and the channels are secured to each bottom truss member with a double strand of 1.2 mm galvanized steel wire, or
(ii)wood joists by way of resilient metal or steel furring channels spaced not more than 406 mm o.c. in conformance with Sentences 2.3.9.(2) and (3), and
(c)a steel furring channel is installed midway between each furring channel mentioned in Clause (b) to provide additional support for the insulation.
(5)Except as required in Sentence 2.3.5.(4), resilient metal or steel furring channels may be used to attach a gypsum board ceiling membrane to a floor assembly using wood joists, metal-plate-connected wood trusses and open-web steel joists, or to a roof assembly. The channels must be made of galvanized steel not less than 0.5 mm thick spaced not more than 610 mm o.c. perpendicular to the framing membranes, with an overlap of not less than 100 mm at splices and a minimum end clearance between the channels and walls of 15 mm.
Open OBC SB-2 in the code viewer
OBC SB-2 2.3.4. Method of Calculation
(1)In the component additive method, the fire-resistance rating of a framed assembly is calculated by adding the time assigned in Sentence (2) for the membrane on the fire-exposed side to the time assigned in Sentence (3) for the framing members and then adding any time assigned in Sentence (4) for additional protective measures, such as the inclusion of insulation or of reinforcement of a membrane. For loadbearing walls where resilient metal channels are installed with a single layer of gypsum board membrane in accordance with Table 2.3.4.A, the fire-resistance rating determined using this method of calculation must be reduced by 10 min.
(2)The times to be used in the component additive method that have been assigned to membranes on the fire-exposed side of the assembly, which are partly based on their ability to remain in place during fire tests, are listed in Tables 2.3.4.A., 2.3.4.B., 2.3.4.C. and 2.3.4.D. (This is not to be confused with the fire-resistance rating of the membrane, which also takes into account the rise in temperature on the unexposed side of the membrane. [See Sentence 2.3.3.(2).])
(3)The times to be used in the component additive method that have been assigned to wall framing members and to floor and roof framing members are listed in Tables 2.3.4.E. and 2.3.4.F. respectively.
(4)Preformed insulation of glass, rock or slag fibre and cellulose fibre insulation provide additional protection to wood studs by shielding the studs from exposure to the fire and thus delaying the time of collapse. The use of preformed glass fibre, preformed rock or slag fibre and dry-blown cellulose insulation material does not decrease the rating of wall assemblies with the membranes identified in Table 2.3.4.A. Similarly, the use of preformed glass fibre, preformed rock or slag fibre and cellulose insulation material does not decrease the rating of floors joists constructed with wood joists, wood trusses, wood I-joists and cold-formed-steel floor joists (C-shaped joists), provided the insulation is not in direct contact with the members identified in Table 2.3.4.B. The use of reinforcement in the membrane exposed to fire also adds to the fire resistance by extending the time to failure. Table 2.3.4.G. shows the time increments that may be added to the fire resistance if these features are incorporated in the assembly.
(5)Cellulose fibre insulation conforming to CAN/ULC-S703, "Standard for Cellulose Fibre Insulation for Buildings", applied in conformance with CAN/CGSB-92.2-M, "Trowel or Spray Applied Acoustical Material", does not affect the fire-resistance rating of a non-loadbearing cold-formed-steel stud wall assembly, provided that it is sprayed to either face of the wall cavity.
Open OBC SB-2 in the code viewer
OBC SB-2 2.3.1. Maximum Fire-Resistance Rating
(1)The fire-resistance rating of walls constructed of wood studs or cold-formed-steel studs, of floors constructed of wood joists, wood I-joists, pre-manufactured wood trusses, cold-formed-steel joists or open web steel joists, and of roofs constructed of wood joists, pre-manufactured metal-plate-connected wood trusses or open web steel joists, can be determined for ratings of not more than 90 min from the information in this Subsection.
Open OBC SB-2 in the code viewer
OBC SB-2 2.3.3. Limitations of Component Additive Method
(See Section 7 Background Information.)
(1)The fire-resistance rating of a framed assembly depends primarily on the time during which the membrane on the fire-exposed side remains in place.
(2)The assigned times in Sentences 2.3.4.(2) to (4) are not intended to be construed as the fire-resistance ratings of the individual components of an assembly, nor are they intended to be construed as times that are applicable or acceptable for use beyond the method and systems described in this Subsection. These assigned times are the individual contributions of each component to the overall fire-resistance rating of an assembly, which are permitted to be derived using the component additive method described in this Subsection.
(3)The fire-resistance rating calculated by the component additive method cannot be increased by installing membranes in multiple layers, other than as specified in Tables 2.3.4.A., 2.3.4.B. and 2.3.4.C.
Open OBC SB-2 in the code viewer
OBC SB-2 1.4.1. Description
(1)For purposes of this Supplementary Standard, concretes are described as Types S, N, L, L_1 , L_2 , L_4 0 S, L_1 20 S or L_2 20 S as described in Sentences (2) to (8).
(2)Type S concrete is the type in which the coarse aggregate is granite, quartzite, siliceous gravel or other dense materials containing at least 30% quartz, chert or flint.
(3)Type N concrete is the type in which the coarse aggregate is cinders, broken brick, blast furnace slag, limestone, calcareous gravel, trap rock, sandstone or similar dense material containing not more than 30% of quartz, chert or flint.
(4)Type L concrete is the type in which all the aggregate is expanded slag, expanded clay, expanded shale or pumice.
(5)Type L_1 concrete is the type in which all the aggregate is expanded shale.
(6)Type L₂ concrete is the type in which all the aggregate is expanded slag, expanded clay or pumice.
(7)Type L40 S concrete is the type in which the fine portion of the aggregate is sand and low density aggregate in which the sand does not exceed 40% of the total volume of all aggregates in the concrete.
(8)Type L_120S and Type L_220S concretes are the types in which the fine portion of the aggregate is sand and low density aggregate in which the sand does not exceed 20% of the total volume of all aggregates in the concrete.
Open OBC SB-2 in the code viewer