When "Framework," Portland's next iconic building, tops out at 12 stories, it will be the nation's tallest structure — and one of the tallest in the world — built entirely of wood. But Framework's most towering achievement may be its stellar environmental performance, including its role in fighting climate change.
Located on Northwest 10th Avenue and Glisan Street in the Pearl District, Framework will feature a novel wood product known as cross-laminated timber (CLT), sometimes described as "plywood on steroids."
Huge CLT panels up to 16 inches thick will compose Framework's walls, floors and roofs, according to the project website. CLT is one of several innovative "mass timber" products, glued panels that are so strong they are being used in place of concrete or steel, in some cases. Another mass timber product, glue laminated timber or glulam beams, will form Framework's structural beams and columns.
Tall all-wood structures once were rare, but now are being embraced by developers in Portland and around the world. They are designed to meet the same fire and earthquake safety performance criteria as comparable steel and concrete structures. But their stellar environmental credentials give them an advantage over other types of structures, according to researchers at the Oregon State University School of Forestry.
In a study released in May, OSU researchers attempted to quantify the environmental benefits of wood over other building materials.
Their study said that the construction and operation of buildings of all kinds are responsible for up to 40 percent of all human-caused greenhouse gas emissions. But when wood is substituted for concrete and steel in the construction of commercial buildings, the OSU study found, emissions of greenhouse gases associated with those buildings could drop by as much as 60 percent.
And when cross-laminated timber products are used instead, greenhouse gas emissions can drop by up to 71 percent, according to a Canadian study cited by the OSU paper.
"A growing tree removes carbon dioxide from the atmosphere, and when it is used in building products, the carbon is sequestered for the life of the building," says Ari Sinha, professor of renewable materials in forestry at OSU and a co-author on the paper.
The world's tallest CLT structure, an 18-story dormitory at the University of British Columbia in Vancouver, just opened. It soon could be dwarfed by an 80-story CLT tower planned for Chicago, and "the Splinter," a 100-story structure proposed in London.
In terms of square footage, the largest all-wood building in the United States is the 156,000-square-foot First Tech Federal Credit Union headquarters in Hillsboro, said Erica Spiritos, an engineer with British Columbia-based Structurlam Products LP. Structurlam is supplying cross-laminated timber for the project, which broke ground this summer.
It also provided the wood for Carbon12, a nearly completed eight-story residential condominium on North Williams Avenue and Fremont Street in Portland, as well as for the UBC dormitory, Spiritos said.
Structurlam, which has an office in the Pearl a few blocks from the Framework site, is bidding to supply its CLT panels, she said.
"CLT can be part of the solution to global climate change," she said, "because we are thoughtfully and sustainably managing our forests to sequester carbon, and simultaneously building cities to be carbon storehouses."
The use of CLT products also can benefit restoration efforts in Northwest forests, said Brent Davies, vice president of forests and ecosystem services at Ecotrust in Portland.
"The type of wood used to construct CLT can come from very small logs and a variety of species, which offers manufacturers the ability to make CLT out of restoration forest products — small logs from forest restoration thinning," Davies said.
Davies told a recent cross-laminated timber conference in Portland that harvests of trees suitable for usage in CLT products could "reduce the risk of severe wildfires, improve habitat, water quality, and forest health, create local jobs and boost rural economies."
D. R. Johnson, based in Riddle in southern Oregon, became the first certified U.S. manufacturer of CLT in 2015. It is producing CLT and glulam for projects in Oregon and beyond.