Mass Timber Construction up to 12 Stories Approved by Vancouver B.C. City Council
Although a vast forest resource may have something to do with it, the adoption within Canada of mass timber for tall wood buildings is also in recognition of wood’s carbon sequestration potential, inherent insulation properties, lighter weight and, as evidenced by the fire testing undertaken since Canada first embraced cross-laminated timber (CLT), its resistance to fire.
The City of Vancouver, allowing from July 1st, 2020, mass timber construction up 12-stories for residential and commercial use, joins municipalities across British Columbia and many other countries around the world which are embracing CLT for ‘green building’ as a contribution towards reducing their GHG footprint. In B.C. that includes flagship projects such as the Brock Commons Tallwood House at the University of British Columbia, which, at the time of its construction was the tallest mass timber building in the world.
It is understood that not all combustible materials behave in the same way* and just as a tightly bound ream of paper does not have the same flammability as a single sheet, so it is with the combustibility of wood when comparing say a matchstick (wood matchsticks are dipped in flammable accelerant to sustain the burn following initial ignition) or piece of kindling with massive wood in the form of CLT.
Although the resistance to fire of large section timbers and glulam has long been recognised the use of CLT for multi-storey buildings has had to be thoroughly put to the test before its use has been permitted by building codes. Testing undertaken by National Research Council Canada and FPInnovations have shown that CLT elements, with or without gypsum board protection, can achieve significant fire resistance, beyond 3 hours in some cases. Tests have also shown that fire stops approved for concrete construction are suitable for CLT elements, so long as adequate detailing is provided.
Is taller safer?
There has also been much research into fire in buildings in Canada particularly given the adoption of CLT in multi-storey buildings with one such study ‘Structure Fires in British Columbia: Exploring Variations in Outcomes as a Function of Building Height and Life Safety Systems’, which takes a closer look at the impact of building height and life safety systems, reported on in Fire Fighting in Canada.
The results may surprise those who equate taller buildings with increased fire safety risk. Not only did buildings with one to four storeys experience more and deadlier fires than taller buildings over the 13-year study period, but the damage and need for fire department intervention tended to decline the higher up in a building the fires started.
Similarly, fires in buildings of any height with working smoke alarms and complete sprinkler protection tended to have relatively low rates of casualties, required less fire department intervention and were largely contained to the room of origin than fires in buildings without those systems. Read more …
*It must be considered as somewhat regrettable that it is the performance in fire of ACM cladding which has led to the unfortunate and illogical UK Government decision to ban the use of CLT within external walls of buildings.
Photos: Brock Commons Tall Wood House