3.1.13.12 — Encapsulated Mass Timber Construction

(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.