When architect Joe Mayo walks into his office, he’s steeped in Seattle history. Mahlum Architects is located in Pioneer Square’s 1910 Polson Building, which served as a warehouse for gold mining equipment during the Klondike Gold Rush. Over the past 100 years, the building has also housed offices and artists’ lofts, and survived two arson fires. So it’s remarkable to see the original old-growth Douglas fir columns still rising from the floor and spanning the ceilings. “It creates a pretty amazing environment,” says Mayo.

Large buildings framed with wood from big trees were commonplace in Seattle and in other parts of the country in the early 1900s. But changing building codes and diminishing availability of large timber put an end to this style. Today, wood buildings are usually one- or two-story houses, while our apartments, hotels and office buildings are nearly all built from concrete and steel. The six-story Bullitt Center on Capitol Hill, which opened in 2013, is the first mid-rise building in Seattle constructed of wood in the past 80 years.

With the advent of a new wood building material called cross-laminated timber (CLT), it might one day become one of many such structures. Proponents say the benefits of building with CLT could be significant. CLT can be used to create buildings that are as tall as 30 stories (and beyond, some architects say) that are better for the environment and aesthetically pleasing, and can be quickly built, help create jobs in economically depressed regional timber towns and are as long-lasting as other buildings. Some research even suggests that wooden buildings offer health benefits for occupants.

Mayo says the material makes sense for our region. “Architecture should feel like it’s a part of a place,” he says. “We’re in the great Northwest, with some of the tallest trees in the world and the best timber in the country, and we have a long history of building with wood.”

But while building codes in Europe and in some other countries have changed to embrace the new material, and CLT buildings as tall as 10 stories are in use in Australia and London, U.S. building codes lag behind. Seattle recently became the first city to allow the use of CLT in construction, but that use is currently limited to five stories for residential buildings and six stories for office buildings.

“The City is open to proposals on larger buildings, but we do have to verify that fire safety and seismic issues have been addressed in the designs,” says Bryan Stevens, spokesperson for the City of Seattle’s Department of Construction and Inspections. That’s because, while these issues have been resolved for buildings in other parts of the world, the U.S. requires domestic testing if building codes are to change.

Washington State University is one participant in a multi-institutional program with the National Science Foundation and the Network of Earthquake Engineering Simulation that is testing how mass timber systems like CLT fare in earthquakes. Hans-Erik Blomgren, a structural engineer in the Seattle offices of the international engineering firm Arup who is a participant in the research program, believes engineers can solve this puzzle. “There’s no technical reason we shouldn’t be designing a building with this material,” he says.

U.S. fire codes have also long prevented the use of combustible materials such as wood in mid- and high-rise buildings, but engineers say code changes to allow for the use of CLT are also achievable. To understand how resistant to fire large pieces of wood can be, proponents suggest thinking of how hard it is to start a bonfire with really big pieces of wood. Not only are such pieces hard to light, but they burn slowly.

In theory, developers could propose larger CLT buildings before codes are changed, but they would have to invest time, money and coordination to get this new building type through Seattle’s Department of Construction and Inspections, with no guarantee that their designs would be approved. “It takes a very special project and specific client and certainly a very ambitious design team to take it on,” says Mayo.

Unless that client steps forward, builders will be waiting for the International Code Council (ICC) to work through the fire and earthquake issues and develop the necessary code changes before mid-rise and higher CLT buildings spring up in the city. 

“We know there’s been a lot of interest in this construction type,” says Stevens, “so we’re trying to be responsive to the demand without giving up safety.”

As with so many innovations, another problem for developers is that material costs for CLT can be high because there are so few North American CLT manufacturers. Developers wait for the price to go down, but manufacturers need more demand for a product. To alleviate this problem, some businesses and legislators are working to help bring CLT mills to Washington state. An Oregon lumber company, D.R. Johnson Lumber, in Riddle, Oregon, recently became the first certified manufacturer of CLT for construction material in the U.S.

Clt was developed in the 1990s by researchers in Austria and Germany who were looking for a use for pieces of surplus wood. The material is created by layering smaller pieces of wood together into a kind of sandwich that offers the strength and insulation found in the massive timbers of the past, and that can be used for the walls, floors, roof beams and posts that make up a building. 

One of the most touted aspects of this material is its role in fighting carbon emissions. Trees absorb carbon and use energy from the sun to grow, which makes them a lower carbon choice than concrete or steel, which not only don’t absorb carbon, but require much more carbon-emitting energy to manufacture. Trees are also a renewable resource, as long as they are harvested from a sustainably managed forest. And CLT can be made from otherwise underused or damaged woods, such as the vast forests of domestic pine that have been killed by mountain pine beetles.

Another selling point, particularly in urban areas, is that CLT panels are prefabricated—bring them to the building site, and your building goes up quickly, with less noise, pollution and traffic delays than with other materials. The eight CLT stories of London’s nine-story Murray Grove apartment building went up in nine weeks.

But building with CLT is not all about practical considerations, says Susan Jones, who owns the Seattle architecture firm Atelierjones and designed her family’s home as the first (and so far only) CLT home in Seattle’s Madison Valley in 2015. The material itself—in the case of her house, CLT primarily from white pine and left unpainted—is a sensual pleasure, from the quality and patina of the wood to the subtle pine smell in the house.

“It’s been incredibly satisfying to live with it,” Jones says. “That’s what architects are asked to do—we create beautiful spaces for people. What’s better than to immerse yourself into this incredibly rich natural environment of wood?”

Here in Washington, there’s enough raw 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 Jones’ CLT house, in the walls of the Bellevue First Congregational Church sanctuary designed by Atelierjones and on a building project at Washington State University in Pullman. In Oregon, Joe Mayo 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.