Cross-Laminated Timber (CLT) is a material beloved of Treehugger because it is made from wood, a renewable resource with low upfront carbon emissions, compared to materials like concrete or steel, which emit a lot of carbon dioxide during their manufacture. 1 De Haro is the first CLT building in San Francisco, but the design by Perkins&Will demonstrates the advantages of mass timber construction go beyond just the storage or avoidance of carbon.
The brochure describes 1 De Haro as “California’s first multi-story, fully mass timber building” but this is not quite accurate; the site has what is called Production, Distribution, and Repair (PCR) zoning that only allows office space to be built if a third of the space is available for light industrial uses. These usually have tougher fire separation requirements, so the ground floor is built of reinforced concrete. The next three floors are built with CLT floors set on glue-laminated columns and beams.
CLT is not the only choice of mass timber when there are beams that can support it. Many buildings are made with nail or dowel laminated timber which can be more economical. Matt Covall, senior project manager on the project, told Treehugger that CLT was appropriate for this job, with its ability to handle long spans; it is dimensionally stable and when combined with the concrete topping acts as a diaphragm.
CLT is manufactured on the west coast in Canada and Oregon, but the material for this project came all the way from Chibougamau, Quebec, home of Nordic Structures, which makes the stuff from its own FSC certified forests. It is a pioneer in the North American mass timber industry, and also assisted in the design and supervised the installation—Covall confirmed that there was quite a bit of French being spoken. Owning the forests would have given them a big advantage in the lumber crisis earlier this year, insulating them from the price spikes.
A major concern with the wood traveling such a distance is the carbon footprint of the transportation, but Nordic moved it all the way from Quebec to Stockton California on a single train; this all gives new meaning to the term flat-pack. It would be interesting to compare that to the footprint of a bunch of ready-mix trucks delivering concrete. As the brochure notes:
The architects provided a carbon accounting for the project, noting: “Life-cycle assessments were performed on the structural system and resulted in a 15% reduction of embodied carbon compared to a concrete structure, when not including biogenic carbon. When including biogenic carbon, the reduction jumped to 51%, resulting in over 2,000 metric ton CO2e reduction.”
I honestly do not understand why excluding the biogenic carbon is even discussed when we are in a climate emergency. What matters is the upfront carbon now, the carbon emissions avoided by using wood now, and the carbon stored in the wood now. In 50 years we might well be feeding the building into a Mr. Fusion machine. I am going with the 51%, 2,000 metric ton carbon dioxide equivalent reductions.
While we come to mass timber for the carbon savings, we stay for many other reasons. The architects tell Treehugger:
It’s lighter: “The site also had poor site conditions, requiring an extensive foundation system. Since a mass timber structure is 20%-50% lighter than a comparable concrete structure, the team could significantly reduce the size of the foundation required, realizing substantial cost and carbon savings.”
It’s thinner: “With a zoning height allowance of just 65’, maintaining the tall ground floor podium required by city planning resulted in floor-to-floor heights of just 12’ – 6”. This limited height would not be ideal for the deep beam depths required for steel construction. CLT and glulam could take advantage of the ability to expose slab ceilings and shallower beam depths.”
It’s quicker: “The project located on a triangular lot in a dense urban environment also benefited from the precision shop manufacturing, resulting in reduced erection schedule, and significantly quieter and less disruptive construction activities.”
It’s just nicer: “The ability to expose the wood structure resulted in a compelling, warm, and inviting space that creates opportunities for traditionally siloed industries to become more integrated into the fabric of the neighborhood, helping to blur traditional boundaries and spur innovation.” Design Director Peter Pfau notes: “It’s amazing how beautiful it is in there. You don’t have to spend money covering up the ugly construction, instead, you just celebrate the beauty of the wood and detailed craftsmanship.”
Lower mass also makes it easier to deal with the lateral loads that you get in earthquakes.
The building is “designed to evoke a jewelry box, its wooden core is wrapped with a glimmering glass curtain wall that illuminates at night.” My first reaction was that we shouldn’t be doing glass jewelry boxes anymore, but this San Francisco, with a very moderate climate, and is a relatively low building with its surface dominated by the roof.
In the grander scheme of things, 1 De Haro is not a ground-breaker. In Europe, it would barely make the news. It’s LEED Gold and has a wonderful green roof. But it is also a speculative development that has to compete in the marketplace with other industrially zoned spaces. It’s like all Perkins&Will buildings: thoughtfully designed and implemented, as green as it can be under the circumstances. It’s on Treehugger because it is the first CLT building in San Francisco, but also because it is so nicely done.
