Interest in sustainable building is on the rise, sparking fierce competition along the building supply chain. That dynamic is already at work in the case of cross-laminated timber and other so-named “mass timber” building elements. As the conflict heats up, real estate professionals need to be prepared for more questions from home buyers and renters, too.
Cross-laminated timber (CLT) refers to layers of wood stacked and glued at right angles. CLT and other mass timber products are rapidly gaining favor as light weight, low carbon building materials, and not just in the single family home market.
With the increased use of mass timber, wood buildings of 10 stories or more are becoming common. The tallest to date is an 18-story student residence in Canada. Japan is set to up the ante with a 70-story skyscraper made of 90 percent wood.
The US Department of Agriculture, for one, is a fan:
Because of its high strength, CLT is an advantageous alternative to traditional building materials such as concrete, masonry, and steel. Because CLT panels resist compression, they are well-suited for building multistory structures, especially mid-rise buildings.
The resistance of CLT to explosion and earthquakes is also a plus.
That leaves fire as an obvious concern. In the latest development, next month the International Code Council plans to vote on a proposal that would provide for wood buildings of up to 18 stories in its Tall Wood Buildings model code.
The stakes are high. Since 1994, ICC has set set model safety and fire prevention building codes for all 50 states and Washington D.C., along with key federal agencies.
For some insight on the fire safety issue, Inman spoke with Samuel Zelinka, a supervisory research engineer with the U.S. Forest Service.
“These are not simply tall ‘stick-frame’ buidings,” Zelinka explained, referring to the familiar 2″x 4″ wood frame construction. “Mass timber is very thick. The performance of wood under fire is has been studied since the 13th century, and it has a very predictable performance.”
When exposed to fire, mass timber forms a layer of char that protects the inner layers. In a building, other protective elements can include gypsum and other wall coverings, as well as sprinklers and other fire suppression infrastructure.
Zelinka’s analysis involved five full scale test compartments set up as residences, complete with furniture and cabinetry. The tests were designed to measure the behavior of fire under different conditions, such as the amount of exposed wood and the use of sprinklers (or not, as the case may be) to suppress fire.
“Scientifically, the reports go through detailed measurements. What we can show is that limited amounts of CLT don’t change the intensity or duration of fire,” said Zelinka.
Similar results were observed in a 2015 study conducted for the government of Quebec.
On the other hand, the Canada-US organization International Association of Fire Chiefs has raised a number of concerns. In particular, the organization cautions that response time is a critical factor, depending on whether or not a multistory wood building is located in an urban jurisdiction with firefighting resources close at hand.
If the ICC does adopt the new proposal, the response time concern suggests that high-rise wood buildings will tend to be located where high-rise buildings are already clustered, namely, in cities and other locations with nearby fire fighting resources.
The technique — shou sugi ban (焼杉板) — originated in 18th century Japan, where it was mainly used to weatherproof cedar exteriors.
Of course, fire safety is only one element in the big picture of resiliency and sustainability.
In a conversation with Inman, Holly Arthur, the Vice President of Communications for the Portland Cement Association, noted the impact of extreme weather events on building lifecycle.
Lifecycle concerns are growing along with the increase in extreme events linked to climate change, including wildfires, storms and floods.
“The greenest building is the one left standing after a disaster,” Arthur said. “You don’t go into your house thinking about it, but the idea of lifecycle is critical.”
Arthur suggests that builders and owners can gain some insights into resiliency through MIT’s “Concrete Sustainability Hub,” a research initiative with which the Portland Cement Association is affiliated.
The project includes an interactive dashboard designed to inform builders and owners about hurricane risk mitigation along the eastern seaboard, comparing a wood baseline to enhanced concrete.
“Many times people don’t realize what their building is made of,” Arthur concludes.
As the number of weather related disasters piles up in the US, that mindset is certainly due for a change.