Code Reference(s):

NBC20, Div. B 3.1.6.6

Subject:

Encapsulation Materials

Title:

Prescriptive Option for 70 min Encapsulation Rating

Description:

This proposed change offers a prescriptive option to achieve the new 70 min encapsulation rating by means of two layers of 5/8” Type-X GWB, in addition to the existing 50 min provision. This roughly mirrors the IBC. (See attached Transferability Report)

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

Related Proposed Change(s):

PCF01, PCF02, PCF04, PCF05, PCF06

PROPOSED CHANGE UNDER PCF1963 (FOR INCLUSION INTO NBC 2025)

3.1.6.6.Encapsulation Materials

1) Gypsum-concrete topping and concrete not less than 38 mm thick are deemed to have an encapsulation rating of 50 min when installed on the upper side of a mass timber floor or roof assembly.

2) Two layers of Type X gypsum board conforming to ASTM C1396/C1396M, “Standard Specification for Gypsum Board,” or CAN/CSA-A82.27-M, “Gypsum Board,” each not less than 12.7 mm thick, are deemed to have an encapsulation rating of 50 min when installed on a mass timber element, provided theyin accordance with Sentence (4).

a) are fastened with a minimum of two rows of screws in each layer

i) directly to the mass timber element with screws of sufficient length to penetrate not less than 20 mm into the mass timber element that are spaced not more than 400 mm o.c. and 20 mm to 38 mm from the boards’ edges, or

ii) to wood furring or resilient metal or steel furring channels not more than 25 mm thick spaced not more than 400 mm o.c. on the mass timber element,

b) are installed with the joints in each layer staggered from those in the adjacent layer,

c) are installed in conformance with ASTM C840, “Standard Specification for Application and Finishing of Gypsum Board”, except that their joints need not be taped and finished, and

d) conform to

i) ASTM C1396/C1396M, “Standard Specification for Gypsum Board”, or

ii) CAN/CSA A82.27 M, “Gypsum Board”.

(See Note A-3.1.6.6.(2).)

3) Three layers of Type X gypsum board conforming to ASTM C1396/C1396M, “Standard Specification for Gypsum Board,” or CAN/CSA-A82.27-M, “Gypsum Board,” each not less than 12.7 mm thick, are deemed to have an encapsulation rating of 80 min when installed on a mass timber element in accordance with Sentence (4).

3)4) The gypsum board described in Sentences (2) and (3) shall be

a) fastened with a minimum of two rows of screws in each layer

i) directly to the mass timber element with screws of sufficient length to penetrate not less than 20 mm into the mass timber element that are spaced not more than 400 mm o.c. and 20 mm to 38 mm from the boards’ edges, or

ii) to wood furring or resilient metal or steel furring channels not more than 25 mm thick spaced not more than 400 mm o.c. on the mass timber element,

b) installed with the joints in each layer staggered from those in the adjacent layer, and

c) installed in conformance with ASTM C840, “Standard Specification for Application and Finishing of Gypsum Board,” except that their joints need not be taped and finished.

(See Note A-3.1.6.6.(24).)

Note A-3.1.6.6. Encapsulation Materials. Research has been conducted on different types of encapsulation materials, such as gypsum board, gypsum concrete and cement board. The results of tests using an intermediate-scale furnace and of cone calorimeter tests indicate that a combustible timber element protected with a 38 mm thick layer of gypsum-concrete topping or with two or threelayers of 12.7 mm Type X gypsum board will not ignite or contribute significant heat to a fire until average temperatures of 325°C to380°C are attained at the interface between the encapsulation material or assembly of materials and the combustible substrate. These temperatures are consistent with the ignition temperatures of wood-based materials.

Note A-3.1.6.6.(24) Protection of Gypsum Board from Foot Traffic. Where gypsum board is used as the encapsulation material on the top of a mass timber floor assembly, it should be protected from physical impact arising from normal pedestrian traffic that could damage it and possibly compromise its encapsulation rating.

ADDITIONAL PROPOSED CHANGE UNDER THIS PCF

3.1.6.6.Encapsulation Materials

1) Gypsum-concrete topping and concrete not less than 38 mm thick are deemed to have an encapsulation rating of 50 min when installed on the upper side of a mass timber floor or roof assembly.

2) One layer of Type X gypsum board conforming to ASTM C 1396/C 1396M, “Standard Specification for Gypsum Board,” or CAN/CSA-A82.27-M, “Gypsum Board,” not less than 12.7 mm thick, is deemed to have an encapsulation rating of 25 min when installed on a mass timber element in accordance with Sentence (6).

2)3)Two layers of Type X gypsum board conforming to ASTM C 1396/C 1396M, “Standard Specification for Gypsum Board,” or CAN/CSA-A82.27-M, “Gypsum Board,” each not less than 12.7 mm thick, are deemed to have an encapsulation rating of 50 min when installed on a mass timber element in accordance with Sentence (4)(6).

4) Two layers of Type X gypsum board conforming to ASTM C 1396/C 1396M, “Standard Specification for Gypsum Board,” or CAN/CSA-A82.27-M, “Gypsum Board,” each not less than 15.9 mm thick, are deemed to have an encapsulation rating of 70 min when installed on a mass timber element in accordance with Sentence (6).

3)5)Three layers of Type X gypsum board conforming to ASTM C 1396/C 1396M, “Standard Specification for Gypsum Board,” or CAN/CSA-A82.27-M, “Gypsum Board,” each not less than 12.7 mm thick, are deemed to have an encapsulation rating of 80 min when installed on a mass timber element in accordance with Sentence (4)(6).

4)6)Installation of the gypsum board described in Sentences (2) and (3)through (5)shall be

a) fastened with a minimum of two rows of screws in each layer

i) directly to the mass timber element with screws of sufficient length to penetrate not less than 20 mm into the mass timber element that are spaced not more than 400 mm o.c. and 20 mm to 38 mm from the boards’ edges, or

ii) to wood furring or resilient metal or steel furring channels not more than 25 mm thick spaced not more than 400 mm o.c. on the mass timber element,

b) installed with the joints in each layer staggered from those in the adjacent layer, and

c) installed in conformance with ASTM C840, “Standard Specification for Application and Finishing of Gypsum Board,” except that their joints need not be taped and finished.

(See Note A-3.1.6.6.(45).)

Note A-3.1.6.6. Encapsulation Materials. Research has been conducted on different types of encapsulation materials, such as gypsum board, gypsum concrete and cement board. The results of tests using an intermediate-scale furnace and of cone calorimeter tests indicate that a combustible timber element protected with a 38 mm thick layer of gypsum-concrete topping or with one (25 min),two (50 min)or three (80 min)layers of 12.7 mm Type X gypsum board or two layers (70 min) of 15.9 mm Type X gypsum boardwill not ignite or contribute significant heat to a fire until the time at whichaverage temperatures of 325°C to 380°C are attained at the interface between the encapsulation material or assembly of materials and the combustible substrate. These temperatures are consistent with the ignition temperatures of wood-based materials.

Note A-3.1.6.6.(46) Protection of Gypsum Board from Foot Traffic. Where gypsum board is used as the encapsulation material on the top of a mass timber floor assembly, it should be protected from physical impact arising from normal pedestrian traffic that could damage it and possibly compromise its encapsulation rating.