Advice provided by: Claire Moloney, LEED Green Associate, Cornell University

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What is Cross Laminated Timber?

Cross-laminated timber is a panel made of wood planks that are stacked crosswise and glued or nailed together. The panels can be used for long spans, such as roofs, floors and walls.

Cross-laminated timber (CLT) is a highly pre-fabricated building material. In fact, CLTs can be fastened together using interlocking profiles (i.e. dovetail connections) instead of glue or fasteners.

Therefore, using CLT reduces construction time - one story of a building can be assembled in a week or less for an average sized floor plan. Similarly, using CLT reduces labor and construction site waste because of its pre-fabrication.

CLT has many additional benefits, including that it’s fire resistant and aesthetically pleasing. Its thick, cross-laminated structure makes it very strong and durable.

Why is Cross Laminated Timber a Green Building Product?

Cross-laminated timber has a lower embodied energy per weight than many other building materials, especially concrete. Also, the highly pre-fabricated panels reduce construction waste, maintain ambient temperatures well (increasing the energy efficiency of the building), and are lightweight, requiring less material for foundation.

According to WoodWorks, an initiative of the Wood Products Council:

“Life-cycle assessment studies show that wood products are responsible for less air and water pollution and fewer greenhouse gas emissions than other materials… the process to manufacture CLT is also energy-efficient and environmentally friendly. Prefabricated panels eliminate jobsite waste, and CLT buildings are proven to maintain their ambient temperatures with less energy."

Since CLT is made of all wood, it is a carbon sink. A carbon sink is a reservoir for carbon, meaning that it "traps" the carbon in solid form and keeps it from entering the atmosphere. Since wood contains carbon, CLT stores more carbon than many alternative non-wood building materials. When this is factored into it’s life cycle analysis, CLT could have a “negative” carbon footprint.

Also, since CLT panels can be constructed without glue or fasteners, and rather fitted with tongue and groove or dovetail joints, the building can be easily deconstructed. This means that the CLT panels can easily be reused in other building applications, which reduces resource depletion and environmental impact.

When Will Cross Laminated Timber Be Available in the U.S.?

CLT is a relatively new technology, developed in the early 1990s in Switzerland. It only started gaining traction in the 2000s with the growth of the green building movement.

While CLT is commercially available in Europe, it isn’t widely available in the U.S., mostly because it hasn’t made economic sense.

However, there have been some projects in the U.S. that have piloted the material and demonstrated its benefits. For example, according to an article in Southern Design and Building, a church in North Carolina was built using the CLT panels. The church was estimated to save 300 metric tons of carbon by using CLT instead of concrete. On top of this, the building costs were 15% less than concrete and it only took the builders 9 weeks to build 9 stories.

A recent article in Treehugger made a great point: the Mountain Pine Beetle is attacking North American trees (and up to 44% of Colorado’s forests), leaving behind a great deal of wood that could be used for CLT.

The University of Utah’s Integrated Technology in Architecture Center is working on a new model of CLT, called interlocking cross-laminated timber (ICLT), which incorporates this "beetle kill" and will be available in the U.S. in the next 3-5 years.

ICLT is similar to the CLT used in Europe, except that the panels are pre-designed to exclude the use of fasteners and adhesives, which will reduce construction costs.

Cross Laminated Timber and LEED

While cross-laminated timber is not readily available in the U.S., it likely will be in the near future given its obvious benefits and continued development. This may have implications for LEED buildings, which may benefit from CLT panels.

For example, CLT panels could potentially help LEED buildings earn credits toward the LEED New Construction rating system.

The following are LEED credits that CLT could directly help a project to earn:

1) Materials and Resources (MR) Credit 3, Materials Reuse: Since buildings made from CLT panels can be easily deconstructed and the panels easily reused, CLT panels could potentially become a popular “reusable” material for LEED buildings.

2) MR Credit 5, Regional Materials: If the CLT panels use locally-sourced wood, it could be considered “regional material”.

3) MR Credit 7, Certified Wood: If the wood used in the CLT panels are certified by the Forest Stewardship Council, the panels could help to earn this credit. To learn more about the "beetle kill" wood (mentioned above) and whether it may qualify for LEED credits, see a previous article on green-buildings.com, "Beetle Kill: Does LEED Consider it Certified Wood?".

4) Energy and Atmosphere (EA) Prerequisite 2, Minimum Energy Performance and EA Credit 1, Optimize Energy Performance: Since CLT panels maintain ambient temperatures without significant energy use, they could help a building to optimize its energy efficiency.

Also, CLT could indirectly contribute to a LEED project since using the highly pre-fabricated CLT panels reduces construction waste. This means that there would be much less construction waste to divert from landfills, making MR Credit 2: Construction Waste Management much easier to achieve.

Related Advice:

• Beetle Kill: Does LEED Consider it Certified Wood?



• Recycled Wood: Reducing Waste Wood in Flooring



• Prefab Green Homes: Ten Sustainable Home Manufacturers to Consider