Articles & Media

(Originally Posted on Plan Washington Website)

Four major challenges facing Washington State might be linked by a common solution: an urban planning revolution towards tall wood buildings.

  • First there’s our booming population growth. The Seattle Metro Area, among the fastest growing in the United States, is expected to gain one million additional residents by 2040. That will require a lot of building to accommodate those new Washingtonians.  
  • The second challenge is climate change. The state’s political system is consumed by competing carbon reduction proposals.
  • Third comes rural poverty. The prosperity enjoyed by many in the Seattle area belies rampant poverty and unemployment in the state’s less populous counties.
  • And finally there’s the wildfire issue. With 1.1 million acres burned, over 200 homes destroyed, and three firefighters killed, 2015 was the worst fire season on record for our state.

What’s the one solution that can help Washington address all four of these issues? It’s a new building material that looks anything but space age to the casual observer: cross-laminated timber (CLT). It’s a wood product made from layers of timber planks oriented at 90 degrees to one another and then glued together.  Originally developed in Europe, CLT can be used as an alternative to concrete, masonry and steel because of its high strength and dimensional stability.

Economic development experts have long sought a mechanism to link the prosperity in our cities with extraction-based rural economies in a sustainable manner. Shifting towards mass timber structures built in cities with product produced in our rural timberlands is a way to establish that linkage. Analysts estimate that domestic CLT manufacturing could become a $4 billion industry. Washington is well-positioned to claim a major piece of that.

“CLT and other advanced wood product technologies are an incredible opportunity for a win-win,” said Colleen McAleer, President of the Washington Business Alliance and a Commissioner at the Port of Port Angeles. “Washington State’s timber industry has been in decline for over 20 years. A sustainable wood product revolution across the US will create an economic opportunity for Washington’s struggling rural communities.”

McAleer, whose Business Alliance has been a leading voice in the carbon reduction policy dialogue, spoke enthusiastically about the positive environmental impact of using wood products in multi-story buildings. “Washington’s working forests are a huge asset in the effort to protect our environment by lowering greenhouse gas in the atmosphere.”



Cross laminated timber (CLT) can reduce greenhouse gas emissions by sequestering carbon inside buildings. Moreover, the carbon reduction benefits of CLT are compounded because of what it’s replacing: energy-intensive building materials like concrete and steel.

In his TED Talk, titled “Why we should build wooden skyscrapers,” Canadian architect Michael Green calculates that if a 20-story building is built out of concrete, producing that material emits 1,215 tonnes of carbon. If CLT is used, the wood product sequesters 3,150 tonnes of carbon, making for a net difference of 4,360 tonnes.

Wood panels are five times lighter than concrete, and 15 times lighter than steel. This means less weight on the foundation and ground underneath.

According to Green, “if we built a 20-story building out of cement and concrete, the process would result in the manufacturing of that cement and 1,200 tonnes of carbon dioxide. If we did it in wood, in this solution, we’d sequester about 3,100 tonnes, for a net difference of 4,300 tonnes.” That’s the equivalent of removing roughly 900 cars from the road for one year.

It is common knowledge that trees benefit the environment by absorbing carbon dioxide. However, the carbon trapping value of trees as carbon stores maxes out somewhere between 30 and 70 years of growth. As trees reach maturity, growth slows and ultimately stops as mortality catches up to growth. Alternately, if one harvests trees on a shorter rotation cycle (let’s say 45 years), replants the inventory, and then creates durable products from the wood, this creates significantly more carbon reduction benefits than if the forest were left untouched. The store of carbon in the forest under a short rotation is reduced below the potential of an older forest, but it is being used instead as a pump to move the forest carbon to other carbon storage pools at the maximum rate that it can be sustainably grown.

Dr. Elaine Oneil is Executive Director of the Consortium for Research on Renewable Industrial Materials (CORRIM). She does a great job summarizing the situation:

“Nature knows how to reduce carbon in the atmosphere by growing trees. This sequesters carbon. It removes it from the air and stores it in the wood. As trees mature the rate that carbon is removed from the atmosphere slows down. As trees die and decompose, they release the carbon back in the atmosphere. So just growing the trees stores carbon but once (and very temporarily). That is not a sustainable reduction unless we use those trees before they mature and plant new trees to replace those used. When trees are cut, they stop removing carbon from the air, but continue to store what was already captured. These trees end up as wood product: desks, cabinets, wood framed buildings.

What does science tell us about how we can remove more carbon from the atmosphere? Cut more trees. We must cut trees, we must replant them, and then use wood products instead of concrete, steel, brick, and plastic. It is ironic, but cutting down trees is one way to save the planet.”

CORRIM is made up of 19 research institutions and advisors from several government agencies. Created to build a scientific databases to quantify the impacts of building with renewable wood materials for construction and other products. Their most recently published fact sheet lays out ten pearls of scientific wisdom from the 40+ peer reviewed studies they’ve produced over their nearly 20-year existence.

CORRIM’s Dr. Oneil stresses the carbon reduction benefits of smartly managed forests. “Growing bigger trees does store more carbon in the trees,” she acknowledged, “but it does nothing for overall carbon reduction because it is only a small part of the system. The way I characterize it in simple terms is, ‘Do you want the forest to be a warehouse or a factory?’ If it is a warehouse then we had better get serious about looking for other ways to reduce CO2 in the atmosphere.”

Mass timber in Washington State

Susan Jones is the founder of the architecture firm atelierjones LLC. She has designed two buildings in the Seattle area that make use of CLT. The CLTHouse was Seattle’s first CLT home — a single family residence in Madison Park. Her second building to use CLT just wrapped up last month. It’s worship space for a Bellevue church, created by renovating the former Star Plaza office building in downtown Bellevue.

Jones says that the US is “far behind Europe” in terms of CLT usage. “It’s a rare instance where they are far outpacing the US in terms of technology and innovation.” The market has steadily grown in the Europe since manufacturing facilities were first established in the early 1990s. Usage has accelerated in recent years as building codes catch up to new findings and society becomes more aware of the carbon sequestration benefits of wood products.

Jones has been tracking the growing usage of CLT for many years. The product was invented in Austria in the early 1990s. “It took time for the authorities to authorize it for building codes and for the market to begin to accept it. It’s been exciting to see the market grow in Austria, Switzerland, Germany, Great Britain, and other countries… The UK is a leader in the technology, but Canada has been quickly catching up. They have two major plants of production: one in BC and another in northern Quebec.”

Jones noted that the US has “just barely” begun to catch on. “There’s one center of production that became active in Southern Oregon during October 2015. D.R. Johnson, a family-owned Southern Oregon timber company, is now the nation’s first supplier of CLT that is certified for use in structural applications. The plant’s opening was fast-tracked through a private-public partnership between D.R. Johnson, Oregon State University, and the state’s economic development agency. This first-in-the-nation CLT press was designed in Washington State by USNR, the world’s largest supplier of equipment and technologies for the wood processing industry.

The first use of these domestically produced CLT panels in a building-wide structural system is currently underway in Portland, OR. The CLT panels are being installed at Albina Yard, a creative office development in north Portland.

Going Forward

In summary, there are many good reasons to build with wood.

  • CLT weighs less than concrete & steel. CLT is approximately one-fifth of the weight of the concrete and one-fifteenth of steel’s weight. This means CLT buildings require a smaller foundation and less interference with existing infrastructure.
  • CLT makes project completion significantly fasterStructural openings, plumbing, and electrical fittings can be incorporated into panels. This high degree of prefabrication means buildings can be manufactured and erected extremely quickly and efficiently. Anecdotally, some 2-year projects can be completed in 3 months when CLT is used.
  • CLT permits design flexibility. Panel thickness can be increased for longer spans. This reduces the amount of interior support elements that are needed. And unlike with steel, when field modifications can be made with simple tools when needed.
  • Using CLT dramatically reduces job site waste. CLT panels are custom manufactured to their final dimensions. Manufacturers can reuse fabrication scraps for stairs and other architectural elements, or as biofuel. Most manufacturers use adhesives that allow CLT to be converted to biofuel pellets when no longer needed at the end of their lifecycle.  
  • CLT buildings trap heat and promote energy efficiency. Since CLT is typically precision-cut using CNC equipment, panel joints fit tightly. Because the panels are solid, there is little potential for airflow through them as well, limiting energy losses.
  • The surface is visually pleasing. Many prefer not to paint over it.
  • CLT provides superior acoustic properties.

All that aside, Jones acknowledged the environmentalist appeal of CLT. “Carbon plays a huge role in why this material is interesting,” she said, “especially to the architectural community. What we specify for materials has a big impact on the environment.” Jones said more work needs to be done in building out the US supply chain so that this low-carbon alternative to steel and concrete is a truly cost-effective option for builders. “It’s hard to compare cost-wise to other conventional building methods and systems,” she admitted. “Though faster construction times and reduced foundation costs might even things out, concrete and steel currently cost slightly less as materials. We don’t have competitive market advantages, the ability to bid between suppliers, or a reliable supply chain.” However, more states are developing CLT production capacity. “Hopefully,” Jones noted, “this will change soon as Oregon, Montana, and Washington State have more plants in production.”

Forterra is currently coordinating an effort with stakeholders to catalyze a CLT market in Washington State.

Beyond the supply chain problem, regulation must shift as well for the CLT revolution to really take root. “Building codes must change,” Jones says. “You can use it here [in the US] but there are limitations to how big your buildings can be.” Jones is one of 18 members on the newly formed ICC ADHoc Committee for Tall Wood Buildings, which has been mandated to update these building codes.

There is a real need for better data on the carbon sequestration benefits of building with CLT. “Common sense tells us that using CLT in place of concrete and steel helps reduce greenhouse gases in the atmosphere,” Jones observed, “but we need to better know the numbers surrounding this.”

It’s time for the environmental, timber, forestry, and building communities to come together on studies in which everyone can feel confident.

The roof of the Richmond Olympic Oval, built for speed skating events at the 2010 Winter Olympic Games in Vancouver, British Columbia, features one of the world’s largest clearspan wooden structures. This is glue-laminated timber, not CLT.

Conceptual plans for a timber skyscraper in Stockholm — Source: Anders Berensson Architects

Lancaster Institute for the Contemporary Arts — Lancaster, UK

Waingels College is a co-educational comprehensive secondary school located in Berkshire, England. This is one of its many CLT buildings: a timber-built performance space.