3.1.6.5 — Determination of Encapsulation Ratings

(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 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 they, (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, “Gypsum Board”, or (ii) CAN/CSA A82.27-M, “Gypsum Board”.