CLT passes the durability test


Seattle Magazine has a long story on cross-laminated timber in its latest issue, laying out the next steps to make CLT more common in the construction of tall buildings in Washington.

Here in Washington, there’s enough raw (CLT) material to immerse us all in that environment. But only a handful of projects in the state have used the material so far—for example, in (Seattle architect Susan) Jones’ CLT house (in Seattle), in the walls of the Bellevue First Congregational Church sanctuary designed by (Jones’ firm) Atelierjones and on a building project at Washington State University in Pullman. In Oregon, (Seattle architect) Joe Mayo (who spoke at the 2013 WFPA annual meeting) recently worked on the design for what is to be the first use of U.S.-made CLT on a two-story building project, using panels manufactured by Oregon’s D.R. Johnson.

There are a few other regional CLT building projects in the design process now. In June, Washington state granted design-build contracts to several architects, including Susan Jones of Atelierjones and Joe Mayo of Mahlum, for 900-square-foot classrooms at several elementary schools in western Washington, to be constructed by the end of 2017.

Another building, Framework, a 12-story building with retail, offices, and housing in Portland, Oregon, is currently in the design process, after a team, which includes Blomgren as its fire and earthquake CLT engineering specialist, won a U.S. Department of Agriculture (USDA) tall wood building competition created to encourage innovation with the material. Winners for 2015, including the Portland team and a team in New York City, each received $1.5 million for the research and development phase of creating buildings using CLT and other engineered wood materials.

At the University of Washington, associate professor of architecture Kate Simonen is leading another USDA-funded study to determine the relative environmental impact of using mass timber in commercial office buildings in Seattle, which follows on other studies indicating that this kind of building will have a lower carbon footprint than other building materials.

The Economist just wrote about CLT developments around the world, including a key test from Oregon State University:

A recent experiment by Skidmore, Owings & Merrill, a firm of architects, and Oregon State University, shows how strong engineered wood can be. The researchers used CLT in a hybrid form known as concrete-jointed timber. This featured an 11-metre wide CLT floor section with a thin layer of reinforced concrete spread across the surface. Thicker sections of concrete were added where the floor was supported by pillars. It was put into a giant test rig where a powerful hydraulic press pushed with increasing force onto the surface. The researchers wanted to see how the structure moved under load, but kept pressing in order to find its limits. The floor finally began to crack when the load reached a massive 82,000 pounds (37,200kg), around eight times what it was designed to support.

Lloyd Alter of TreeHugger, in a recent column calling on wood to replace concrete in construction wherever appropriate, cited another Economist article about the carbon footprint of cement, a major ingredient in concrete. The concrete industry has staged a lobbying effort against CLT.

The cement industry is one of the world’s most polluting: it accounts for 5% of man-made carbon-dioxide emissions each year. Making this most useful of glues requires vast quantities of energy and water. Calcium carbonate (generally in the form of limestone), silica, iron oxide and alumina are partially melted by heating them to 1450°C in a special kiln. The result, clinker, is mixed with gypsum and ground to make cement, a basic ingredient of concrete. Breaking down the limestone produces about half of the emissions; almost all the rest come from the burning of fossil fuels to heat the kiln.