3.1.6.13 — Combustible Stairs

(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) Except as provided in Sentences (3) to (6), Sentence 3.1.6.3. (4), Articles 3.1.6.7. and 3.1.6.12. and Sentences 3.1.6.16. (2) and 3.1.6.17. (2), 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. (2) Except as provided in Sentence 3.1.6.11. (1), the material or assembly of materials referred to 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 materials listed in Clauses (a) to (d). (3) Except as provided in Sentence (5), 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) the aggregate surface area does not exceed 10% 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. (4) Except as provided in Sentences (5) and (6), 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, and (b) the flame-spread rating on any exposed surface is not more than 150. (5) 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. (6) The exposed surfaces of mass timber ceilings within a suite need not be protected in accordance with Sentence (1), provided the aggregate area of the exposed surfaces does not exceed, (a) 10% of the total ceiling area of the suite, where the exposed surfaces have a flame-spread rating not more than 150, or (b) 25% of the total ceiling area of the suite, where, (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.