Flashpoint: November 2012
By Peter Sells
I shuddered when I read about this, but first impressions can be deceiving:
By Peter Sells
I shuddered when I read about this, but first impressions can be deceiving: architect Michael Green has proposed a 10-storey wooden building in Prince George, B.C., with ambitions for a 30-storey wooden skyscraper in Vancouver. I was picturing traditional wood-frame construction, essentially a towering tinderbox in the sky. Then I looked at what Green is actually proposing.
The proposed Wood Innovation and Design Centre will become a test case for creating a value-added forest products industry around tall wood building construction methods that would differ radically from the way traditional mid-rise and even highrise buildings are built. Green’s TWBs (tall wood buildings) would have more in common structurally with old-style construction, which featured robust masonry, load-bearing walls and full dimensional lumber floor and roof members. But in TWBs, everything is made of wood.
Essentially, the mass timber building systems, as proposed, would create all vertical and horizontal building components out of laminated veneer lumber, laminated strand lumber and cross-laminated timber. Each solid section of wall, floor or roof would be custom designed and constructed for its purpose, with no hidden voids or spaces within.
I downloaded Green’s report, The Case for Tall Wood Buildings: How Mass Timber Offers a Safe, Economical, and Environmentally Friendly Alternative for Tall Building Structures, and read the section on fire performance. I found that Green has a complete understanding of active and passive fire-protection strategies, propagation of flame, heat and smoke, and protection of occupants. Some highlights:
- The old, heavy timber construction methods recognized that heavy timber members that have been damaged by fire still retain structural capacity in the non-charred section. Using this principle as a basis for design, mass timber structural members can be designed to have a sacrificial layer of wood that would act as a protective layer against fire.
- TWB project design would include a degree of compartmentalization: limiting the potential spread of fire beyond the compartment of origin. Green recognizes that it would also be necessary to consider the risk or probability of fire spread due to system or sub-system failure.
- An encapsulation approach would incorporate the installation of two layers of 16-millimetre type-X gypsum board directly to the exposed surfaces of the mass timber materials, using positive fastening devices, such as screws, of sufficient depth to resist deterioration and pull-out during fire exposure. Don’t you wish that all architects could think their way through fire protection so completely? Gypsum-board layers would incorporate staggered, overlapping joints to maintain solid, continuous thermal protection of the underlying wood. Encapsulation is preferred to charring, to minimize the production of smoke, which could jeopardize occupants.
- Green has considered exterior auto-exposure. All exterior occupied spaces such as balconies, ground level patios with building overhangs above and similar exterior spaces will be sprinkler-protected to minimize potential fire ignition and vertical spread on the building exterior.
- All interior spaces are protected by sprinklers and smoke detection as per British Columbia codes.
Green certainly has all of his wooden ducks in a row, but there is an echo in the back of my head of Capt. Peter McBride’s building construction course. McBride, an incident safety officer with Ottawa Fire Services, said, “Remember, we fight fires in buildings as built, not as designed.” Applying his cautionary point would suggest that fire services should vigorously and aggressively inspect these new TWBs.
As of March, British Columbia had received 34 expressions of interest from design/build firms. As for why, Green says, “We stopped exploring wood around 100 years ago (with the advent of steel and concrete); now we’re looking at a whole new system using mass-timber products.”
TWBs aren’t just an alternative for the sake of being different. “The real change came when we started thinking about climate change,” Green says. “Steel and concrete are great but not environmentally friendly.”
Canada’s timber industry is green, renewable, and employs thousands of workers. Wood locks in CO2 until it is burned, whereas the manufacturing of steel and concrete have a large carbon footprint.
“We think we can go higher than 30 storeys,” says Green.
I wooden bet against it.
Retired District Chief Peter Sells writes, speaks and consults on fire service management and professional development across North America and internationally. He holds a B.Sc. from the University of Toronto and an MBA from the University of Windsor. He sits on the advisory council of the Institution of Fire Engineers, Canada branch. Peter is president of NivoNuvo Consulting, Inc, specializing in fire-service management. Contact him at firstname.lastname@example.org