Code Reference(s):

NBC20, Div. B 3.1.6.4

Subject:

Encapsulation of Mass Timber Elements

Title:

Expanding Encapsulation Rating Requirements Based on Hazard

Description:

This proposed change (PCF01) lays the foundation for mirroring the IBC structure of three different tiers of required encapsulation rating (‘noncombustible protection’ in the IBC) based off hazard. Instead of the existing 50 min rating for all EMTC, readers will be directed to a Table in new Article 3.2.2.93. for the applicable encapsulation rating. (See PCF04) Existing relaxations regarding wood exposure for medium-level hazard buildings (those with a 50 min encapsulation rating) will stand. Exposure allowances described in Sentences (3) to (7) have been updated to harmonize with upcoming changes in the 2025 NBCC. No relaxations will be offered for the new higher-hazard EMTC tier (70 min encapsulation rating), thereby implying full encapsulation. With the addition of a new Sentence, the new lower-hazard EMTC tier (0 min) will be exempted from encapsulation requirements, except in select critical locations.

Related Proposed Change(s):

PCF01, PCF03, PCF04, PCF05, PCF06

PROPOSED CHANGE UNDER PCF1870 (FOR INCLUSION INTO NBC 2025)

3.1.6.4.Encapsulation of Mass Timber Elements

(See also Note A-3.1.6.3.)

1) Except as provided in Sentences (3)(to 6)to (7), 3.1.6.3.(4), 3.1.6.16.(2) and 3.1.6.17.(2), and Articles 3.1.6.7. and 3.1.6.12., the exposed surfaces of structural mass timber elements conforming to Article 3.1.6.3. shall be protected from adjacent spaces in the building, including adjacent concealed spaces within wall, floor and roof assemblies, by a material or assembly of materials conforming to Sentence (2) that provides an encapsulation rating of not less than 50 min. (See Note A-3.1.6.4.(1).)

2) Except as provided in Sentence 3.1.6.11.(1), the material or assembly of materials referred to in Sentence (1) shall consist of

a) gypsum board,

b) gypsum concrete,

c) noncombustible materials,

d) materials that conform to Sentences 3.1.5.1.(2) to (4), or

e) any combination of the materials listed in Clauses (a) to (d).

3) Except as provided in Sentences (5) and (7), the exposed surfaces of mass timber beams, columns and arches within a suite or fire compartment need not be protected in accordance with Sentence (1), provided

a) their aggregate exposed surface area does not exceed 1035% of the total wall area of the perimeter of the suite or fire compartment in which they are located, and

b) the flame-spread rating on any exposed surface is not more than 150. (See Note A-3.1.6.4.(3) to (6)Note A-3.1.6.4.(3) to (7).)

4) Except as provided in Sentences (5) and (6)and (7), the exposed surfaces of mass timber walls within a suite need not be protected in accordance with Sentence (1), provided

a) each exposed surface faces the same direction, andall portions of the exposed surfaces

I. face the same direction, or

II. II. are separated by a horizontal distance of not less than 4.5 m, and

b) the flame-spread rating on any exposed surface is not more than 150.

(See Notes A-3.1.6.4.(4) and A-3.1.6.4.(3) to (6)and A-3.1.6.4.(3) to (7).)

5) Except as provided in Subclause (7)(b)(ii),Tthe aggregate exposed surface area of mass timber elements within a suite permitted in Sentences (3) and (4) shall not exceed 35% of the total wall area of the perimeter of the suite. (See Note A-3.1.6.4.(3) to (6)Note A-3.1.6.4.(3) to (7).)

6) Except as provided by Sentence (7),Tthe exposed surfaces of mass timber ceilings within a suiteor fire compartment, other than an exit or public corridor, need not be protected in accordance with Sentence (1), provided their aggregate surface area does not exceed

a) 10% of the total ceiling area of the suiteor fire compartment,where the flame-spread rating on any exposed surfacesishave a flame-spread rating not more than 150, or

b) 25% of the total ceiling area of the suite or fire compartment,where the flame-spread rating on any exposed surface of a mass timber wall or ceiling is not more than 75.

i)the suite contains no mass timber walls with exposed surfaces, and

ii) the exposed surfaces of the mass timber ceiling have a flame-spread rating not more than 75.

(See Note A-3.1.6.4.(3) to (6)Note A-3.1.6.4.(3) to (7).)

7) The exposed surfaces of mass timber ceilings within a suite need not be protected in accordance with Sentence (1) or (6), provided

a) the aggregate surface area of any exposed mass timber beams, columns and arches does not exceed 20% of the total wall area of the perimeter of the suite in which they are located,

b) all surfaces of mass timber walls are

i) protected in accordance with Sentence (1), or

ii) where the aggregate exposed surface area of mass timber elements exceeds the limit specified in Sentence (5), protected by a material or assembly of materials conforming to Sentence (2) that provides an encapsulation rating of not less than 80 min, and

c) the flame spread rating on any exposed surface of a mass timber wall or ceiling is not more than 75. (See Note A-3.1.6.4.(3) to (7).)

Note A-3.1.6.4.(3) to (76)Fire-Resistance Rating of Mass Timber with Exposed Surfaces. Portions of mass timber elements required to have a fire-resistance rating are permitted to be exposed in accordance with the permissions stated in Sentences 3.1.6.4.(3) to (6)to (7); however, it is important to note that applying those permissions does not waive the requirement for these elements to have a fire-resistance rating.

Note A-3.1.6.4.(4)Exposed Surfaces of Mass Timber Walls. The primary objective of encapsulating mass timber elements is to limit the probability that these elements will significantly contribute to fire spread and fire duration in the event of a fire. Since thick wood members require a source of imposed heat flux to burn, the stipulation inClause 3.1.6.4.(4)(a) stipulates that any portions ofthe exposed surfaces of different mass timber walls within a suite eitherface the same direction within a suiteor have a minimum horizontal distance between one another. If the sprinkler system fails to operate or to control the fire, this directional orientation or minimum distance is intended to avoid orreduce the potential offor re-radiation between portions ofburning mass timber surfaces on different walls, and particularly thosethat either face or are in close proximity toeachone another, which could sustain flaming combustion into the decay phase of a fire.if the sprinkler system failed to operate or to control the fire. Additionally, if the sprinkler system fails to operate or to control the fire,the maximum percentages of exposed surface areas and maximum flame-spread ratings stated in Article 3.1.6.4. is loware intended to beso that it is notinsufficient to sustain a ventilation-controlled fire that might provide the radiation required to sustain flaming combustion into the decay phase of a fire.if the sprinkler system failed to operate or to control the fire.

ADDITIONAL PROPOSED CHANGE UNDER THIS PCF

3.1.6.4.Encapsulation of Mass Timber Elements

(See also Note A-3.1.6.3.)

1) Except as provided in Sentences (3) to (7)(9), 3.1.6.3.(4), 3.1.6.16.(2) and 3.1.6.17.(2), and Articles 3.1.6.7. and 3.1.6.12., the exposed surfaces of structural mass timber elements conforming to Article 3.1.6.3. shall be protected from adjacent spaces in the building, including adjacent concealed spaces within wall, floor and roof assemblies, by a material or assembly of materials conforming to Sentence (2) that provides an encapsulation ratingof not less than 50 min.that

a) is not less than 50 minutes in a building or part of a building constructed in conformance with Article 3.2.2.48 or 3.2.2.57, or

b) conforms to the minimum values stated in Table 3.2.2.93. for the applicable major occupancy and building height.

(See Note A-3.1.6.4.(1).)

2) Except as provided in Sentence 3.1.6.11.(1), the material or assembly of materials referred to in Sentence (1) shall consist of

a) gypsum board,

b) gypsum concrete,

c) noncombustible materials,

d) materials that conform to Sentences 3.1.5.1.(2) to (4), or

e) any combination of the materials listed in Clauses (a) to (d).

3) Except as provided in Sentences (5) and (7), the exposed surfaces of mass timber beams, columns and arches within a suite or fire compartmentin a building or part of a building constructed in conformance with Article 3.2.2.48 or 3.2.2.57 or permitted by Article 3.2.2.93. to have a 50 min encapsulation rating need not be protected in accordance with Sentence (1), provided

a) their aggregate exposed surface area does not exceed 35% of the total wall area of the perimeter of the suite or fire compartment in which they are located, and

b) the flame-spread rating on any exposed surface is not more than 150. (See Note A-3.1.6.4.(3) to (7)(8).)

4) Except as provided in Sentences (5) and (7), the exposed surfaces of mass timber walls within a suitein a building or part of a building constructed in conformance with Article 3.2.2.48 or 3.2.2.57 or permitted by Article 3.2.2.93. to have a 50 min encapsulation rating need not be protected in accordance with Sentence (1), provided

a) all portions of the exposed surfaces

I. face the same direction, or

II. are separated by a horizontal distance of not less than 4.5 m, and

b) the flame-spread rating on any exposed surface is not more than 150.

(See Notes A-3.1.6.4.(4) and A-3.1.6.4.(3) to (7)(8).)

5) Except as provided in Subclause (7)(b)(ii), the aggregate exposed surface area of mass timber elements within a suite permitted in Sentences (3) and (4) shall not exceed 35% of the total wall area of the perimeter of the suite. (See Note A-3.1.6.4.(3) to (7)(8).)

6) Except as provided by Sentence (7), the exposed surfaces of mass timber ceilings within a suite or fire compartment,other than an exit or public corridor,in a building or part of a building constructed in conformance with Article 3.2.2.48 or 3.2.2.57 or permitted by Article 3.2.2.93. to have a 50 min encapsulation rating need not be protected in accordance with Sentence (1), provided their aggregate surface area does not exceed

a) 10% of the total ceiling area of the suite or fire compartment, where the flame-spread rating on any exposed surface is not more than 150, or

b) 25% of the total ceiling area of the suite or fire compartment, where the flame-spread rating on any exposed surface of a mass timber wall or ceiling is not more than 75. (See Note A-3.1.6.4.(3) to (7)(8).)

7) The exposed surfaces of mass timber ceilings within a suite need not be protected in accordance with Sentence (1) or (6), provided

a) the aggregate surface area of any exposed mass timber beams, columns and arches does not exceed 20% of the total wall area of the perimeter of the suite in which they are located,

b) all surfaces of mass timber walls are

i) protected in accordance with Sentence (1), or

ii) where the aggregate exposed surface area of mass timber elements exceeds the limit specified in Sentence (5), protected by a material or assembly of materials conforming to Sentence (2) that provides an encapsulation rating of not less than 80 min, and

c) the flame spread rating on any exposed mass timber wall or ceiling is not more than 75. (See Note A-3.1.6.4.(3) to (7)(8).)

8) Structural mass timber elements in a building or part of a building permitted by Article 3.2.2.93. to have an encapsulation rating of 0 min need not be protected in accordance with Sentence (1), provided

a) mass timber walls and ceilings within vertical service spaces, public corridors, and exits are protected from adjacent spaces with a material or assembly of materials conforming to Sentence (2) that provides an encapsulation rating of not less than 25 min, and

b) concealed spaces are protected in conformance with 3.1.6.3.(4).

(See Note A-3.1.6.4.(3) to (8).)

9) In a building or part of a building required by Clause 3.1.6.4.(1)(b) to have a minimum encapsulation rating of 70 min, the upper side of a mass timber floor or roof assembly is permitted to be encapsulated by a material or assembly of materials conforming to Sentence 3.1.6.4.(2) that provides an encapsulation rating of 50 min.

Note A-3.1.6.4.(3) to (78)Fire-Resistance Rating of Mass Timber with Exposed Surfaces. Portions of mass timber elements required to have a fire-resistance rating are permitted to be exposed in accordance with the permissions stated in Sentences 3.1.6.4.(3) to (7)(8); however, it is important to note that applying those permissions does not waive the requirement for these elements to have a fire-resistance rating.