Developers can now construct mass timber buildings in 91原创 up to 18 storeys tall.
City council approved changes Tuesday to the building bylaw to increase the current height limit of 12 storeys for “encapsulated mass timber” construction to 18 for residential and commercial uses.
The changes also allow mass timber construction to be used in the development of schools, light and medium-industrial buildings and care facilities. More exposed mass timber will also be allowed inside buildings, but only under certain circumstances.
“Allowing taller mass timber construction and expanding the use of mass timber to new building types and uses within the building bylaw will make it easier to build with low carbon materials, support future housing affordability and represent an important step in reducing our carbon pollution from construction,” said a staff report that went before council Tuesday.
Mass timber is made of smaller pieces of lumber, which are laminated together to form engineered structural components for floors, walls, columns and beams.
But is mass timber fire safe?
It was a question posed by Coun. Lenny Zhou to Saul Schwebs, the city’s chief building official.
“In certain cases, it can be safer than light frame wood construction, but compared to a concrete building, it’s probably equivalent, perhaps a little more fire safe in certain circumstances,” said Schwebs, noting the thickness of the material.
“When there is a fire in a mass timber building, we see charring that takes place, and the charring actually helps protect the remainder of the structure.”
Schwebs qualified his answer, noting that questions related to fire safety are based on testing and modelling, not an actual fire to a mass timber building. He said he wasn’t aware of any mass timber buildings that have caught fire.
“There hasn’t been a whole lot of study done following a fire in an 18-storey mass timber building,” he said. “There’s just been modelling that’s been done, or testing that’s been done, which is not reality.”
'May cause confusion'
Concerns were raised in the report by staff about exposing mass timber in residences.
The B.C. building code permits a certain percentage of wall and ceiling areas to omit the encapsulation protection. In 91原创, however, it has previously been recognized that allowing partially exposed mass timber within a suite could encourage the removal of the encapsulation protection.
This, effectively, exposes more or all of the mass timber in the suite, creating “an unacceptable risk to fire safety,” said the report, noting once a suite is occupied, there is no means for investigators to inspect and ensure the building’s fire protection is maintained.
Shawn Keyes, executive director of Woodworks BC, told council that he supported the city’s move to allow taller mass timber construction. At the same time, Keyes said he was concerned about restricting the amount of exposed mass timber in residential buildings nine to 12 storeys tall.
“The additional requirements for gypsum wall board — encapsulation — within the City of 91原创 may cause confusion for the design and construction community and reduce their ability to provide consistent solutions across the province,” Keyes said.
In response, Coun. Sarah Kirby-Yung successfully added an amendment to the revised bylaw that would have staff seek to align the city’s bylaw with senior government regulations, so not to preclude exposed mass timber in residences.
Earthquake
According to the city staff report, mass timber is five times lighter than concrete and that difference can be advantageous in a building’s ability to withstand an earthquake.
“It can be much easier and more cost-effective to design mass timber buildings to a higher seismic standard, and modular components can make it easier to repair, reducing the time needed to resume occupancy after a large earthquake,” the report said.
In 2007, a joint Italian-Japanese research team tested a seven-storey mass timber building on a “shake table.” They found that it could withstand the seismic forces of the 1995 earthquake in Kobe, Japan, which destroyed more than 50,000 buildings.
“Because wood is a lighter material than concrete and steel, soils with reduced bearing capacity can support taller buildings constructed from wood compared to concrete and steel structures,” the report said. “This advantage allows construction on marginal soils.”
Tallwood House student residence
91原创 proper does not have any examples of an 18-storey mass timber building, but one was built recently at the University of B.C. Tallwood House student residence at Brock Commons is one of the tallest mass timber buildings in the world.
Other examples of mass timber buildings include a luxury condo project called Terrace House on West Hastings Street and the 10-storey Nature’s Path head office, which is under construction near the East Van sign at Clark Drive and Great Northern Way.
Both projects were approved under what the city calls an “alternative solutions process,” where building code and fire experts review applications that go beyond provisions in a building code, which at the time allowed for only six storeys.
In 2020, council amended the bylaw to include encapsulated mass timber as a new construction type and allow new developments up to 12 storeys.
“Since then, many [mass timber] buildings, both in Canada and around the world, have been successfully constructed that exceed the prescriptive boundaries of what the 91原创 building bylaw would permit,” the report said.
“With the supporting research and real-world application, these buildings have demonstrated that they are both safe and practical.”
'Hybrid timber'
Mass timber construction is not to be confused with “hybrid timber.”
Hybrid-timber construction includes a combination of heavy steel columns and beams, a concrete core and cross-laminated timber floor slabs topped in concrete. The method has fewer design and functional limitations than an all-mass timber construction.
In January, council approved a rezoning application from Henriquez Partners Architects on behalf of Westbank Projects Corp. for a 25-storey “hybrid timber” rental highrise at Main Street and 5th Avenue.
Other examples of hybrid timber projects approved or that were under review in January included: 1190 Burrard St. (social housing, service centre, 17 storeys), 1055 Dunsmuir St. (office,16 storeys), 3571 Sawmill Cres. (residential, 18 storeys) and the new 91原创 Art Gallery (11 storeys) across from the Queen Elizabeth Theatre.
