The new Brock Commons student residence at the University of British Columbia will be the tallest contemporary mass timber building in the world when finished this May. The term “mass timber” or “mass wood” covers an array of approaches, usually referring to a structural system combining engineered wood columns and floor slabs. In Canada, the most commonly referenced technical innovation, and one of the ones behind Brock Commons’ structure, is the cross-laminated timber (CLT) slab, available in a variety of thicknesses for different span requirements.
While Brock Commons’ height will unquestionably get the lion’s share of attention after its completion, that’s not the most interesting thing about the building for architects. Rather, it is the fact that, on typical floors, the wood is not visible.
Acton Ostry Architects principal Russell Acton, FRAIC, the lead designer of Brock Commons, has lectured widely on the project. When he talks to architectural audiences, he is inevitably asked: “why didn’t you expose the wood?” The answer is that the wood structure has been encapsulated in drywall and concrete topping to ensure efficient code compliance.
This pragmatic approach was a response to achieving quick approvals, and as an associated outcome, addressed perceptual challenges in terms of fire safety. In fact, the historic (and completely understandable) fear of fire in wood frame buildings is dramatically less relevant to mass timber. During a fire, the outside surface of a thick wood member chars while protecting a structural core of unburnt wood. As building codes develop, it is likely that the testing of mass wood assemblies will assist authorities to better understand the inherent fire resistance of mass timber, and potentially reduce the need for encapsulation, provided that a sacrificial layer of wood char is provided in its place.
From Canadian Architect: https://www.canadianarchitect.com/features/reaching-new-heights-2/