Code Reference(s):

NBC20, Div. B 3.1.6.9

Subject:

Encapsulation Clading

Title:

Tiered permissions for combustible cladding

Description:

A change is proposed to Article 3.1.6.9. of the 2020 NBC to allow for variations in cladding as a function of the EMTC building height, including those that are proposed as new EMTC building types in new Article 3.2.2.93. Currently, the NBC requirements for cladding are generally a function of required/permitted type of construction. This means, for example, that even though a building constructed of EMTC in conformance with Article 3.2.2.48. (Group C, up to 12 storeys, Sprinklered) of the 2020 NBC may only be 1 storey in building height, the type of cladding is restricted on the same basis as to what is permitted for a 12-storey building constructed of EMTC under the same Article. As implied by the existing provisions of Clause 3.1.5.5.(1)(a), the fire spread risk associated with combustible cladding generally increases with increasing building height, and potentially to a lesser degree as a function of building area (i.e., greater building area typically equates to larger building facades). Therefore, given that the new proposed EMTC building area limits are constant with building height, it is proposed to consider options for varying the requirements for cladding construction as a function of building height and provide more direct alignment between degree of combustibility of cladding and fire risk. The proposed cladding options as a function of building height for the current NBC 2020 and the new Sentence 3.2.2.93. EMTC building types are summarized in Table 1.

Table 1: Proposed Cladding Requirements as a Function of EMTC Building Height

Building Height, Storeys NC S135 S134 3.1.6.9. 3.1.4.8. C
1-4 P P P P P P
5, 6 P P P P P NP
7-12 P P P P NP NP
13+ P P P NP NP NP
  • P = Permitted
  • NP = Not Permitted
  • NC = Noncombustible
  • C = Combustible
  • S135 = A material or combination of materials that satisfy the criteria of Sentence 3.1.5.1.(2) when tested in accordance with CAN/ULC-S135, “Standard Method of Test for Determination of Degrees of Combustibility of Building Materials Using an Oxygen Consumption Calorimeter (Cone Calorimeter)”
  • S134 = A wall assembly that satisfies the criteria of Clause 3.1.5.5.(1)(b) when tested in accordance with CAN/ULC-S134, “Standard Method of Fire Test for Exterior Wall Assemblies”

*Note: this proposed change was provided by the Joint Task Group – Harmonized Variations for Mass Timber*

Related Proposed Change(s):

PCF01, PCF02, PCF03, PCF05, PCF06

PROPOSED CHANGE

3.1.6.9.Exterior Cladding

1) Except as provided in Sentences (2), (3), (4), (6) and (6)(9), cladding on an exterior wall assembly of a building or part of a building permitted to be of encapsulated mass timber construction shall be

a) noncombustible,

b) a material or combination of materials that satisfy the criteria of Sentence 3.1.5.1.(2),

c) except as provided in Sentence (7), a wall assembly that satisfies the criteria of Clause 3.1.5.5.(1)(b), or

d) a combination of the cladding described in Clauses (a) to (c). (See Note A-3.1.6.9.(1), and (2), (4) and (6).)

2) Except as provided in Sentences (3), to(4), (6) and (5)(8), cladding on an exterior wall assembly of a building or part of a building permitted to be of encapsulated mass timber construction that is not more than 12 storeys in building height is permitted to consist of

a) combustible cladding that

i) is not contiguous over more than 4 storeys,

ii) represents not more than 10% of the cladding on each exterior wall of each storey,

iii) is not more than 1.2 m in width,

iv) has a flame-spread rating not more than 75 on any exposed surface, or any surface that would be exposed by cutting through the material in any direction,

v) is separated from other portions of combustible cladding on adjacent storeys by a horizontal distance of not less than 2.4 m, and

vi) is separated from other portions of combustible cladding by a horizontal distance of not less than 1.2 m,

b) combustible cladding that

i) is not contiguous across adjacent storeys,

ii) represents not more than 10% of the cladding on each exterior wall of each storey,

iii) has a flame-spread rating not more than 75 on any exposed surface, or any surface that would be exposed by cutting through the material in any direction, and

iv) is separated from other portions of combustible cladding on adjacent storeys by a horizontal distance of not less than 2.4 m,

c) combustible cladding representing up to 100% of the cladding on exterior walls of the first storey, provided all portions of the cladding can be directly accessed and are located not more than 15 m from a street or access route conforming to Article 3.2.5.6., measured horizontally from the face of the building, or

d) except as provided in Sentence (4), a wall assembly that satisfies the criteria of Clause 3.1.5.5.(1)(b), or

e)d) a combination of cladding described in Sentence (1) noncombustible cladding and the cladding described in Clauses (a) to (d)(c).

(See Note A-3.1.6.9.(1), and (2), (4) and (6).)

3) The permitted area of combustible cladding in Clause (2)(a) or (b) shall not exceed 5% of the cladding on each exterior wall of each storey where the time from receipt of notification of a fire by the fire department until the arrival of the first fire department vehicle at the building exceeds 10 min in 10% or more of all fire department calls to the building. (See Note A-3.2.3.1.(8).)

4) Except as provided in Sentences (6) and (8), cladding on an exterior wall assembly of a building or part of a building permitted to be of encapsulated mass timber construction that is not more than 6 storeys in building height is permitted to consist of

a) combustible cladding that

i) represents not more than 10% of the cladding on each exterior wall of each storey, and

ii) has a flame-spread rating not more than 75 on any exposed surface, or any surface that would be exposed by cutting through the material in any direction, or

b) a combination of the cladding described in Clause (a) and the cladding described in Sentence (1) and Clause (2)(c).

(See Note A-3.1.6.9.(1), (2), (4) and (6).)

7)5) Where combustible cladding conforming to Clause (2)(a), or (b) or (4)(a) on an exterior wall of a fire compartment is exposed to combustible cladding conforming to Clause (2)(a), or (b) or (4)(a) on an exterior wall of the same fire compartment or of another fire compartment, and the planes of the two walls are parallel or at an angle less than 135° measured from the exterior of the building, the different portions of combustible cladding shall

a) be separated by a horizontal distance of not less than 3 m, and

b) not be contiguous over more than 2 storeys.

6) Except as provided in Sentence (8), cladding on an exterior wall assembly of a building or part of a building permitted to be of encapsulated mass timber construction and not more than 4 storeys in building height is permitted to consist of combustible material with a flame-spread rating not more than 75 on any exposed surface, or any surface that would be exposed by cutting through the material in any direction. (See Note A-3.1.6.9.(1), (2), (4) and (6).)

4)7) An exterior wall assembly constructed in conformance with Section D-6 of Appendix D is deemed to satisfy the criteria of Clause (2)(d)(1)(c).

5)8) Except as provided in Article 3.2.3.10., where the limiting distance in Table 3.2.3.1.-D or 3.2.3.1.-E permits an area of unprotected openings of not more than 10% of the exposing building face, the construction requirements of Table 3.2.3.7. shall be met.

6)9) A wall assembly conforming to Clause (2)(d)(1)(c) that includes combustible cladding made of fire-retardant-treated wood shall be tested for fire exposure after the cladding has been subjected to the accelerated weathering test specified in ASTM D2898, “Standard Practice for Accelerated Weathering of Fire-Retardant-Treated Wood for Fire Testing.”

3.2.3.7.Construction of Exposing Building Face

Table 3.2.3.7. – Minimum Construction Requirements for Exposing Building Faces – Forming Part of Sentences 3.1.6.9.(5) and 3.2.3.7.(1) to (4)

Occupancy
Classification of Building or Fire Compartment

Maximum Area of Unprotected Openings
Permitted, % of Exposing Building Face Area

Minimum Required Fire-Resistance
Rating

Type of Construction
Required

Type of Cladding Required

 

 

 

Group A, B, C, D, or Group
F, Division 3

0 to 10

1 h

Noncombustible

Noncombustible

>10 to 25

1 h

Combustible,
Encapsulated mass timber
, or Noncombustible

Noncombustible

>25 to 50

45 min

Combustible,
Encapsulated mass timber
, or Noncombustible

Noncombustible

>50 to <100

45 min

Combustible,
Encapsulated mass timber
, or Noncombustible

Combustible or Noncombustible(1)(2)

 

 

 

 

 

Group E, or Group F,
Division 1 or 2

0 to 10

2 h

Noncombustible

Noncombustible

>10 to 25

2 h

Combustible,
Encapsulated mass timber
, or Noncombustible

Noncombustible

>25 to 50

1 h

Combustible,
Encapsulated mass timber
, or Noncombustible

Noncombustible

>50 to <100

1 h

Combustible,
Encapsulated mass timber
, or Noncombustible

Combustible or Noncombustible(2)

Notes to Table 3.2.3.7.:

(1) The cladding on Group C buildings conforming to Article 3.2.2.51. and on Group D buildings conforming to Article 3.2.2.60. shall be noncombustible or consist of a wall that satisfies the requirements of Article 3.1.4.8.

(2) The cladding on Group C buildings or parts thereof conforming to Article 3.2.2.48. and on Group D buildings or parts thereof conforming to Article 3.2.2.57. buildings or parts thereof conforming to Articles 3.2.2.48., 3.2.2.57. or 3.2.2.93. shall conform to Sentence 3.1.6.9.(2)Article 3.1.6.9. or be noncombustible.

Note A-3.1.6.9.(1) , and (2), (4) and (6) Exterior Cladding. The requirements in Sentences 3.1.6.9.(1), and (2), (4) and (6) are intended to reduce the potential for fire spread on the exterior cladding of buildings of encapsulated mass timber construction through the use of noncombustible finishes on the exterior of the wall assembly or the use of a cladding/wall assembly that has been proven to resist flame propagation as a function of increasing building height, including provisions to allow 100% combustible cladding where the height does not exceed 4 storeys. These cladding/wall assembly combinations can be used as infill or panel-type walls between structural elements, or attached directly to a loadbearing structural system. Note that the requirements in Article 3.1.6.9. do not supersede the provisions in Subsection 3.2.3. regarding spatial separation and exposure protection.