3.1.6.4 — Encapsulation of Mass Timber Elements

(1) Except as permitted by Sentences (2) to (4) and Articles 3.1.5.2. to 3.1.5.25., 3.1.13.4. and 3.2.2.16., a building or part of a building required to be of noncombustible construction, shall be constructed with noncombustible materials. (2) Notwithstanding the definition for noncombustible materials stated in Article 1.4.1.2. of Division A, a material is permitted to be used in noncombustible construction provided that, when tested in accordance with ULC S135, “Test Method for the Determination of Combustibility Parameters of Building Materials Using an Oxygen Consumption Calorimeter (Cone Calorimeter)”, at a heat flux of 50 kW/m2, (a) its average total heat release is not more than 3 MJ/m2, (b) its average total smoke extinction area is not more than 1.0 m2, and (c) the test duration is extended beyond the time stipulated in the referenced standard until it is clear that there is no further release of heat or smoke. (3) If a material referred to in Sentence (2) consists of a number of discrete layers and testing reveals that the surface layer or layers protect the underlying layers such that the complete combustion of the underlying layers does not occur, the test shall be repeated by removing the outer layers sequentially until all layers have been exposed during testing, or until complete combustion has occurred. (4) The acceptance criteria for a material tested in accordance with Sentence (3) shall be based on the cumulative emissions from all layers, which must not exceed the criteria stated in Clauses (2)(a) and (b).

(1) Wood nailing elements are permitted to be used for the attachment of a material or assembly of materials to provide an encapsulation rating in a building or part of a building permitted to be of encapsulated mass timber construction, provided the concealed space created by the wood nailing elements is not more than 25 mm deep. (2) Except as permitted by Sentence 3.1.6.16. (2) and Article 3.1.6.6., wood nailing elements are permitted to be used for the attachment of interior finishes in a building or part of a building permitted to be of encapsulated mass timber construction, provided the concealed space created by the wood nailing elements is not more than 50 mm deep and, (a) exposed surfaces in the concealed space have a flame-spread rating not more than 25, or (b) the concealed space is filled with noncombustible insulation.

(1) Wood members that are more than 50 mm but not more than 300 mm high are permitted to be used for the construction of a raised platform in a building or part of a building permitted to be of encapsulated mass timber construction, and they need not conform to Articles 3.1.6.3. and 3.1.6.4., provided, (a) the concealed spaces created by the wood members are divided into compartments by fire blocks in conformance with Sentence 3.1.11.3. (4), and (b) the wood members are, (i) applied directly to or set into a noncombustible floor slab, or (ii) applied directly to a mass timber floor assembly that conforms to the requirements of Article 3.1.6.3. (2) The upper surface of the mass timber floor assembly referred to in Subclause (1)(b)(ii) is permitted to be encapsulated only between the wood members by a material or assembly of materials conforming to Sentences 3.1.6.4. (1) and (2). (3) The floor system for the raised platform referred to in Sentence (1) is permitted to include a combustible subfloor and combustible finished flooring.

(1) Except as provided in Sentence (2) and Article 3.1.11.7., and except as otherwise provided in this Subsection, only construction materials and components permitted in noncombustible construction shall be permitted to have exposed surfaces in concealed spaces within floor, roof and wall assemblies permitted in a building or part of a building permitted to be of encapsulated mass timber construction. (2) Exposed surfaces are permitted in a concealed space created by the attachment of a material or assembly of materials conforming to Sentence 3.1.6.4. (1), provided the concealed space is not more than 25 mm deep.

(1) The minimum dimensions stated in Table 3.1.6.3. need not apply at cutouts in vertical or horizontal structural mass timber elements where outlet boxes are installed in accordance with Article 3.1.9.3A. (2) The exposed surfaces of the cutouts described in Sentence (1) need not be protected in accordance with Sentence 3.1.6.4. (1). (3) Outlet boxes on opposite sides of a structural mass timber element having a fire-resistances rating shall be separated by a distance of not less than 600 mm.

(1) Except as otherwise provided in this Subsection and Articles 3.2.2.16. and 3.2.3.19., a building or part of a building permitted to be of encapsulated mass timber construction is permitted to include structural mass timber elements, including beams, columns, arches and wall, floor and roof assemblies, provided they comply with Sentences (2) and (3). (2) Structural mass timber elements referred to in Sentence (1) shall, (a) except as provided in Sentence (4), be arranged in heavy solid masses containing no concealed spaces, (b) have essentially smooth flat surfaces with no thin sections or sharp projections, and (c) except as provided in Sentence 3.1.6.17. (1), conform to the minimum dimensions stated in Table 3.1.6.3. (3) Adhesives used in structural mass timber elements referred to in Sentence (1) that are constructed of cross-laminated timber shall conform to the elevated temperature performance requirements in ANSI/APA PRG 320, “Standard for Performance-Rated Cross-Laminated Timber”. (4) Concealed spaces are permitted within structural mass timber elements referred to in Sentence (2) and need not conform to Sentence 3.1.6.4. (1) provided the concealed spaces are, (a) sprinklered and divided into compartments by fire blocks in conformance with Subsection 3.1.11., (b) completely filled with rocks or slag fibre insulation conforming to CAN/ULC-S702.1 “Standard for Mineral Fibre Thermal Insulation for Buildings, Part 1: Material Specification” and having a density not less than 32 kg/m3, (c) if horizontal, lined with not less than a single layer of 12.7 mm thick Type X gypsum board or noncombustible material providing an encapsulation rating of not less than 25 min, or (d) if vertical, lined with not less than a single layer of 12.7 mm thick Type X gypsum board or noncombustible material providing an encapsulation rating of not less than 25 min and vertically divided into compartments by fire blocks in conformance with Subsection 3.1.11.

(1) Wood roof sheathing and roof sheathing supports that do not conform to Articles 3.1.6.3. and 3.1.6.4. are permitted in a building or part of a building permitted to be of encapsulated mass timber construction, provided they are installed, (a) above a concrete deck in accordance with Clauses 3.1.5.3. (2)(a) to (f), or (b) above a deck of encapsulated mass timber construction, where, (i) the deck is permitted to be encapsulated between the roof sheathing supports by a material or assembly of materials conforming to Sentence 3.1.6.4. (2) that provides an encapsulation rating of not less than 50 min, (ii) the height of the roof space is not more than 1 m, (iii) the roof space is divided into compartments by fire blocks in conformance with Article 3.1.11.5., (iv) openings through the deck other than for noncombustible roof drains and plumbing piping are protected by shafts constructed as fire separations having a fire-resistance rating not less than 1 h that extend from the deck to not less than 150 mm above the adjacent sheathing, and (v) except as permitted by Subclause (iv), the roof space does not contain any building services. (2) Combustible cant strips, roof curbs, nailing strips and similar components used in the installation of roofing are permitted on a building or part of a building permitted to be of encapsulated mass timber construction. (3) Wood nailer facings to parapets that are not more than 610 mm high are permitted on a building or part of a building permitted to be of encapsulated mass timber construction, provided the facings and any roof membranes covering the facings are protected by sheet metal.