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KPFF Consulting Engineers managing partner Blake Patsy wants to push the envelope with a traditional building material.

Patsy and THA Architecture principal David Keltner are studying how high-rises could be built with wood instead of steel and concrete. It’s feasible, and worth taking advantage of a building material that is both sustainable and affordable, said Patsy, a structural engineer.

“We thought it would be a good idea to study this,” he said. “I think wood is a great material. Each material has its place in a particular project. You just have to explore all your options.”

Other Portland-area engineers and architects also are intrigued by cross laminated timber and other sturdier and more fire-resistant wood products that make it easier to build higher with lumber. But building code restrictions that limit timber structures to about five stories because of fire safety concerns and the relative obscurity of cross laminated timber would make it tricky to get a high-rise project using the prefabricated wood paneling system off the ground in Portland.

“There is no code for (cross laminated timber) to meet right now, so that’s a big hurdle,” Keltner said.

Federal involvement

Cross laminated timber panels are manufactured with lumber that is glued in opposing directions to form a solid slab that can be used for walls, floors or ceilings. The product has gained popularity in Europe over the past 20 years, but it’s still relatively unused in the U.S.

However, the U.S. Department of Agriculture is now pushing for construction of more wood-frame high-rise buildings. In an effort to support the U.S. timber industry, the federal agency is partnering with Washington, D.C.-based nonprofit WoodWorks to inform architects, engineers and contractors of the benefits of cross laminated timber.

The USDA also plans to invest $1 million to launch a prize competition, likely later this year, to encourage the design and development of high-rise wood demonstration projects.

Cross laminated timber expands the construction possibilities for wood, WoodWorks Executive Director Jennifer Cover said. This is why the organization , she said, in its workshops, webinars and informational fairs, including two upcoming events in Portland.

“There is a general lack of awareness of where wood can be used safely,” Cover said. “There needs to be more education for engineers on wood products, especially when it comes to building higher.”

Portland could be pioneer

Portland is suited to be a pioneer in high-rise wood-frame construction, Keltner said.

“I have felt like our city, of all the cities in the U.S., should be the place this is first,” he said. “Politically, our city is really well known for its sustainability, and this is a big part of why this makes sense. Also, there is such a great long tradition of building with lumber in the Northwest. Plus, it’s a major industry in our state.”

Portland code limits wood-frame buildings to five stories, but it’s possible to engineer a taller one, Patsy said. Wood’s flammable properties complicate the issue, he said. Stick-frame buildings can burn to the ground in minutes, which is one reason for the code restrictions, he said.

“Structurally, is it OK? Yeah it is,” he said. “That’s going to be the easy part. It’s fire (risk) that’s going to be more difficult.”

The advantage of cross laminated timber is that, like heavy timber beam construction, the panels will char instead of igniting, Patsy said.

“The charring process keeps the fire from totally eating up the beam,” he said. “When you get into the two-by stuff, that will go up like toothpicks.”

Wood’s lightness and flexibility means that a high-rise wood-frame building should perform well in an earthquake, Patsy said. One concern with using cross laminated timber is the seismic strength of connections between the panels, Keltner said.

“The problem is you have to connect all these panels together with fasteners, and those are notoriously weak,” he said. “That’s the big engineering feat right now: … how to get those connections to work in (an earthquake).”

City code is ‘pretty silent’

So far, Portland has approved only one cross laminated timber project – a small, single-story structure that soon will be built at the Oregon Zoo, said Amit Kumar, a senior structural engineer with the city. Others have inquired about using the product, but architects and engineers would have to first prove that it can meet fire safety and seismic requirements, he said.

“Unfortunately, right now the building code is pretty silent on those types of products,” he said. “They have to demonstrate that it can be used effectively.”

Extra calculations for load capacity were required to gain city approval for use of cross laminated timber on the roof of the 2,000-square-foot zoo building, Equilibrium Engineers associate JoMarie Farrell said. The prefabricated panels allow for a roof that cantilevers over the building – the design intention of SRG Partnership, she said.

“Without this product, we would have had to add some structural supports,” she said. “It provides that thin profile that architects like to see. That’s one of the big pros.”

Farrell said she can see cross laminated timber used for high-rise buildings, but challenges await.

“Given our high seismic design criteria in this area, it seems like it would be tough to do anything above four stories,” Farrell said. “It’s so new it might take us several years before we start using it on anything that’s taller.”

Code limitations are one reason why it may take a while before a developer is willing to construct a high-rise wood building in Portland, Patsy said.

“It’s risky for a developer to do it because they invest all this money in design fees and then they design something that may not be approvable,” he said. “It can be dangerous for people doing the first step.”

If you go …

What: “The Case for Cross Laminated Timber: Opportunities and Challenges” seminar

When: April 18, from 11 a.m. to 2 p.m.

Where: Morton’s The Steakhouse, Portland

Cost: $20

More information: woodworks.org

What: Oregon Wood Solutions Fair

When: Oct. 23

Where: Oregon Convention Center, Portland

Cost: Free

More information: woodworks.org