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May 20, 2013

Letter to the Editor: Cross-laminated timber needs champion in U.S.

By Jean-Marc Dubois
Nordic Engineered Wood

I'd like to clarify a couple of points that are made in the April 22 DJC article on cross-laminated timber that may prove misleading for your readers. Chiefly, that no high-rise buildings have been constructed in seismic areas. In fact, Italy, which has seen a growing number of earthquakes recently, is home to a number of nine-story apartments that are made of CLT.

These buildings were modeled after testing a number of full-scale CLT buildings for resistance to seismic impact on the world's largest shake table, in Kobe, Japan. In fact, there are videos of the testing available for viewing: http://b.vimeocdn.com/ts/108/345/108345844_295.jpg

The tests validated not just the resistance to seismic activity, but also the fact that after 14 different tests not only was the building self-righting (off by less than 4mm from vertical), it was livable post-disaster. Compare this to the Christchurch, New Zealand, earthquake that destroyed hundreds of buildings. While they may have allowed the occupants to remain alive, the reality of these “earthquake-proof” buildings is that they now need to be razed in order to rebuild.

In addition to the seismic performance, despite being “combustible,” CLT, being a massive timber composition, has very specific and predictable fire-resistant properties. Unlike steel and concrete, which can appear to be safe because they are not burning yet can fatigue and fail without warning, burning wood creates a char layer that protects the structural portion of the element in question.

There are any number of pictures available showing steel girders melted and draped over wood beams in buildings that were destroyed by fire. The telling statement in your article was the question of why wood is not being used more: Is it a performance issue or is it a perception issue?

European fire departments, including in London where the Waugh-Thistleton Stadthaus was built, actually prefer wood to steel and concrete due to its predictability.

In fact, after reviewing the fire-resistance and earthquake resistance of CLT panels, Japan has fast-tracked the incorporation of CLT into its building code. CLT heralds in a new era for fast, safe, efficient and affordable housing. As your article points out, a champion is required to lead the way in North America.

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