When it comes to fire tests, boring is best.
You roll apocalyptic fire directly into the face of some dumb panel of cross-lminated timber (CLT) and nothing happens! Flames lick the slab for hours, leaving only char, a blackened scab stubbornly insulating the multiple layers that shield the core. What does this remind you of from Boy Scout days past? That’s right! Vainly attempting to light a bonfire without first laying some tinder under the logs.
Of course, it was the stick construction that gave us all that tinder to burn down Chicago in 1871, laying the groundwork for more than a century of steel and concrete. But that era may be coming to an end. After all, when you look at those boring fire tests, one thing that is slightly less boring is the slow melt and imminent collapse of steel framing.
One glaring problem of this traditional approach is that all the excitement comes with a high cost in carbon emissions. Cross-laminated timber leaves a far lighter footprint, claim its advocates. Instead of spewing carbon, trees sequester it, a single tree locking up a ton of the sooty stuff when harvested in forty years. Thinned and replanted with less density, forests become healthier and less susceptible to fire, their yields of small-diameter timber for CLT a benefit, rather than a waste.
As for costs in dollars, never a boring subject, CLT construction is already on a par with traditional construction in Europe and Canada. And as new CLT plants go up in Montana, Oregon, and Maine, the industry is on track in the U.S., as well. The new tariffs on steel could accelerate this cost competitiveness even more.
But the main thing about CLT is the seamless digital link that this technology has made possible between architecture and construction. Unlike steel and cement, wood yields itself easily to precision CNC cutting off-site, every barcoded panel comes delivered for assembly exactly to the architects’ BIM and Rhino specs. Architecture and construction in concert at last: the potential for Talmudic disputes between disciplines over interpretation recedes dramatically. In the digitized world of CLT, the architect can now take part in the building process every step of the way, instead of keeping manufacturing and construction at arm’s length once the client has the plans.
More involvement, more liability. But a growing number of architects, like Susan Jones, FAIA, find this new mode of design and construction well worth the risk.
As a little girl summering on an island in Puget Sound, Jones recalls marveling at what her grandfather pointed out was the connection between trees and lumber, saplings that could one day make houses: Sitka spruce, Western and Ponderosa pines, and the big daddy of all, Douglas fir. The poetry and evanescence of that moment continue to live within her, she writes in her new book, Mass Timber, helping to drive the success of her purposefully small, fifteen-year-old Seattle firm atelierjones.
Rated seventh out of the top fifty in design by Architecture magazine last year, atelierjones has produced four CLT buildings, more than any other firm in the States so far, though it’s a record she predicts she won’t hang on to for long—which is fine by her. Let CLT grow and prosper! As the AIA’s point person on the International Code Council (ICC), Jones was happy to endure endless committee meetings in windowless airport hotels if only for a chance to get CLT approved for high-rises by the assembled fire chiefs, engineers, and officials. And she is almost there, a million dollars’ worth of tests later, with just the ICC full membership vote still pending.
In Mass Timber, Jones explains why all the emphasis is on building CLT high-rises, as opposed to homes. In her view, it’s a matter of Carbon Good and Carbon Great. For a single-family house, you still need exterior cladding, a rain screen, and water-proofing barrier, and 2 x 6 studs stuffed with insulation, plus either gypsum wallboard or CLT. Choose CLT over the studs and wallboard and you’ve got Carbon Good. Unlike houses, high-rises are mainly reinforced concrete. Swap that out for CLT slabs, while leaving only the concrete foundation—and you achieve Carbon Great.
“America is often ahead in technology, but in construction, we’re twenty years behind, and it’s time to catch up,” says Jones. “One has but to look at the successful high-rise CLT buildings that have gone up in London (the Dalston Lane), Norway (the Treet), and Vancouver (The Tallwood Residency), all over a hundred feet.” Overflow attendance at the Building Energy Exchange and Passive House conferences in New York this June speak to a growing interest.
Mass Timber, she explains, is a general term that includes not only CLT, but other hypermaterials made from trees: DLT (dowel laminated timber), NLT (nail laminated), and glulam beams and columns. But whatever it is, Mass Timber has nothing to do with log cabins, Mass Timber and CLT represent a revolution in the building industry, much like steel and concrete afforded modernist architects over a century ago.
Today, the heirs to those architects can turn a dried and warp-proofed, cross-laminated and pressed panel 40’ x 8’ x 4” into something beautiful that has never been imagined before. In atelierjones’ house project, panels rest on each other “like a house of cards.” Inside the church and school projects, instead of boring, ubiquitous gyp, there’s real, honey-colored wood, finger-jointed and CNC-cut.
Here is where the visionary architect Kenneth Frampton’s tectonic culture comes to life. Here, in the work of atelierjones, structural detail and a collaborative construction model become design poetry! CLT becomes sublime, a hyper-material that synthesizes the Hegelian dialectic between structure and ornament.
A different paradigm. CLT affords Jones the ability to wed structure and ornament in a tectonic union.
Yes, ornament. The CNC cutouts, the lofty “house of cards” juxtapositions of the CLT panels, the way they can be set to rest on each other’s shoulders like Fred Astaire and Gene Kelly hamming it up, the surfaces of finger-joints, knots and grains, as opposed to plain gyp. And perhaps most decorative of all, the blue fungus stains left in pinewood courtesy of the Dendroctonus ponderosae beetle that has of late destroyed millions of acres of timber from British Columbia to Mexico. But how stunning the blue stains look on interior walls! And what’s even more not-boring, according to Jones, is the fact that moldy, substandard wood can now be put to use structurally, as middle layers sandwiched inside the CLT.
Now, swing back from the ornamental to the structural. Counter-intuitively but logically, the fire issue is less of one: lumber chars for hours, the tinder that is today's stick construction goes up in seconds. But how about CLT standing up to seismic shock?
Will the CLT skyscrapers of the future fall like a house of cards, or Fred Astaire and Gene Kelly collapsing in some kind of pratfall?
Judith Sheine is a Professor at the Department of Architecture, University of Oregon, and the Director of Design at the TallWood Design Institute. A state-funded collaboration with Oregon State, TallWood dominates the advanced timber products research space in the U.S. For Oregon, a big win is possible. Instead of felling and shipping logs for ports abroad, its workforce will be upping their skills considerably, rning those logs into high-tech materials with a digital handshake.
Just as crucial for TallWood and the industry as a whole is CLT's ability to resist lateral forces, the ability of tall timber buildings to withstand everything from hurricane winds in the Caribbean to—more immediately—the seismic shock of earthquakes along the Cascadia fault line. Currently, Sheine and her staff are testing the CLT panels destined for LEVER Architecture’s new, 12-story, Framework Building in Portland, OR.
While on the phone, Sheine waves a student named Russell into her office. Russell is elatedly holding up a model of a leading-edge lateral force resisting system called a Rocking Wall. Developed by one of the pioneers of advanced wood construction, structural engineer Andrew Buchanan, of Christchurch, New Zealand, Rocking Walls for high-rise CLT structures represent a dramatic departure from conventional seismic design, which depends largely on the ductility of various “members” of a structure, while accepting that some damage is inevitable. Look no further than the 2016 Valentine’s Day Quake in Christchurch for multiple examples of cracked concrete structures.
Timber Rocking Wall systems simply rocked back into place, which is the cause of Russell and Prof. Sheine’s excitement.
In this model, high-strength steel rods—or tendons—run through the CLT panels, having been post-tensioned through a central duct. Those rods plus U-shaped steel connectors between the panels allow the CLT building core to rock in a quake, while at the same time dissipating the acoustic shock. If things get really bad, Sheine explains, and the rods or connectors break, the wood will still rock into place, leaving only that those rods and connectors be replaced, not the entire structure.
In addition to teaching and design directing at Tallwood, Sheine is a prominent scholar of the Austrian-born architect Rudolph Michael Schindler (1887-1953), whose work was mainly around Los Angeles. Schindler, says Sheine, would have “embraced the possibilities of CLT and Mass Timber right away because it can be digitally fabricated into whatever shapes and textures you want. And like concrete and corrugated fiberglass for his time, Schindler liked the idea of exposing the structure, rather than hiding it under layers and layers. He wanted the truth of the building to stand out: what is holding up the building is also the finish of the building.”
According to Judith Sheine, Susan Jones and other innovators, the digitization of CLT and Mass Timber make such truthfulness and tectonic realization all the more possible. And this may be the ultimate test—at least something to think about during the long hours spent watching timber char in a fire test.