When it comes to choosing building materials for a major project that has to withstand Ontario’s volatile weather patterns, science has to be the prime consideration, architect Alex Lukachko told a crowd attending his seminar titled Six-Storey Construction: Wood or Concrete at the recent Construct Canada show.
"There is a lot of interest in whether this is going to make sense from a finance perspective and also thinking about the building-science-related issues," said Lukachko, a Toronto-based senior consultant with the RDH Building Science Inc., in an interview.
"Three-storey construction, we have a long history with and we know all the ins and outs of how wood works in three storeys. As you move it up to five- and six-storey construction you are dealing with issues that are the same as low rise but…more significant with the high-rise construction."
With a 13-storey tall-wood structure under construction in Quebec, a 14-floor wood project completed in Bergen, Norway and an 18-storey wood student residence underway in Vancouver, the enthusiasm for these structures continues to grow, he said.
British Columbia and Washington state are among North America’s leaders in terms of number of projects while thought leaders like the multinational firm Perkins+Will promote such benefits as wood being "made by the sun, completely renewable, and able to absorb and sequester carbon throughout its lifetime" as well as creating "a special quality of space, contributing to a feeling of warmth and well-being."
With successful examples of tall wood structures showcasing the product around the world, the stage was set for amendments to Ontario’s Building Code that permitted six-storey wood buildings as of January 2015, said Lukachko.
He started his seminar with an elemental discussion of the properties of existing building materials such as steel, masonry, stone, clay brick and various forms of concrete, comparing them to the modern mass-timber products such as cross-laminated timber (CLT), laminated strand lumber (LSL) and laminated veneer lumber (LVL) that have helped fuel the growth of tall-wood projects.
All types of building materials have flaws, said Lukachko. Natural and ambient elements such as wind, rain, temperature extremes, salt and other corrosives, UV exposure and wear and tear are all enemies that degrade building materials, and act with varying severity depending on where the structure is built.
Lukachko says that designers and builders are increasingly looking to use new building materials in new situations, and if they opt for wood in tall projects, among the issues they must address is the possible need for insulation on the outside, the possibility of water penetration and water movement through the wall, possible wood shrinkage, wood acoustics and air-tightness.
Industry strengths and imperatives and even political ones also play a role in the choice of materials, he said.
For example, Ontario’s concrete industry is a strength whereas wood is stronger in B.C. — so it might make sense, and be most cost-efficient, to choose a material where there is an abundance of expertise.
Another issue is thermal control, said Lukachko. "In wood frame construction, when you get to six storeys, you are losing some of that cavity, because you are filling it with wood structure, you are losing the connection with the approach that we have traditionally used with low-rise construction, where you just add insulation in the void created by the frame. So to get the R value that you need for modern construction, you’ve got to move that insulation to the outside."
At the same time, he said, "You are dealing with wood exposure to moisture at six storeys, and shrinkage issues where you’ve got to…accommodate the wood shrinkage."
Fire hazard studies are continuing as wood gains in popularity, but, says Lukachko, moisture is the biggest problem with wood. Ontario builders will have to adopt new practices if they want to use it for tall wood projects.
He showed a slide that indicated how a rainstorm hits a tall wood building, creating a pattern similar to a hose being sprayed directly onto a surface – the water sheets to the sides and gathers and then drains down to the ground floor, creating a potentially damaging accumulation of water in certain locations.
"From a water management perspective, taller buildings are exposed to greater driving rain loads, so the solutions that we use for low-rise construction management, we have to think carefully about how we are going to do that on taller buildings," Lukachko said.
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