Mar 23, 2023
How a Seattle Architect Helped Make Timber Towers Legal in the US
(Bloomberg) -- When it opens in a few months, a new apartment complex in Seattle will be the first of its kind: specifically, the first building project in the US to break ground under a new category in the construction code, which allows for the structural use of mass timber — a group of engineered, extremely strong wood components— up to a height of 85 feet, or eight or nine stories. (Another new category allows wood structures as tall as 18 stories if certain additional requirements are met.)
For its architect, Susan Jones, it’s not so much a first as the culmination of a decade spent researching, building with, and advocating for the use of wood in modern construction. Jones, who runs the small design studio atelierjones LLC in Seattle, is one of the leading authorities on mass timber in the US. She has completed several projects — including modular school classrooms, a church sanctuary and her own home — using varieties of the material.
She also helped devise and run rigorous tests in 2017 to try to answer the question that held back mass timber’s use in the US years after it caught on in Europe: Could it withstand fire? The tests, conducted on full-scale mock apartments in a federal research lab, showed that the wood forms an outer char layer when it burns that slows the progression of the fire and protects the wood’s core.
Bloomberg Green spoke to Jones as the apartment project, Heartwood, nears completion. The interview has been edited and condensed for length and clarity.
How and when did you become interested in designing with timber?
When I was a graduate student, and we had to do our first structural piece, it was a wooden pavilion. That was the first and last time I was ever asked in graduate school to design out of wood.
Read more: Why Wood Is the Breakout Architecture Star of the Early 21st Century
Much later in my career, I was revisiting the idea of what it means to design your own house. How wood feels in a space really came back to me, from the experiences I had as a child growing up in the Pacific Northwest and living in structures that surrounded one with wood — both in this little tiny cabin that my grandparents built in the San Juan Islands in the early 1950s, and a house that my parents built in the mid-1960s. I remember touching the cedar on the living-room walls of our house, and what that felt like and what that smelled like. So when I had the chance to build my own house in 2010, ’11 and ’12, that opportunity began to kind of reveal and present itself.
Tell us about Heartwood.
Heartwood is a 126-unit workforce housing project. It’s serving middle-income tenants. It’s owned and managed by this very venerable nonprofit here in town called Community Roots Housing. This was a big departure from their core mission of deep affordability. All of their projects to date have been publicly funded because of the affordability. But no public subsidies were used at all [on Heartwood], with the exception of the [$250,000] Wood Innovations grant that I was thrilled to get from the US Forest Service in 2019. It should be finished in July after a fairly accelerated construction schedule and lots of prefabrication.
It has an entire superstructure [that is, all the aboveground parts of a building] of mass timber, with the exception of the lateral bracing — seismic bracing — which is steel, and a very modest concrete foundation because of the lightness of wood coming down on this eight-story building.
Even with some steel and concrete, there’s a lot of wood in the building. Did you calculate the carbon savings from using it?
We’re in the middle of doing a comparative lifecycle assessment, which means that we’re modeling a concrete building to compare to our Heartwood mass timber building. And then we are doing lifecycle analyses of the carbon footprints for both of those buildings, through the University of Washington. We believe that the timber superstructure of our building, compared to the superstructure of a concrete building, will be approximately 40% lower. [Jones later clarified that this does not include the sequestered carbon in the mass timber superstructure. When that is factored in, the carbon footprint should be net-negative, she said.]
How much cost did using timber extensively add?
It’s probably going to be about a wash. If you just compare wood versus concrete, those costs go way up for wood. That’s really the danger in looking at it as just a substitution effect, because you have to look at it holistically to get those kind of numbers to pencil at all. But if you have the right team, who understand the timber building as a holistic system, and can work very clearly with a goal towards the maximum [amount of] prefabrication, the savings potentially come in [a shorter construction schedule]. If [leasing] can happen earlier, and you can have a couple of extra months’ worth of rent, then that really begins to balance out the entire cost equation.
Where did you source the wood?
A lot of our peers in the US have been sourcing their timber from Europe. It is a bit of a hard decision to make as an architect to turn your back on the European market. But in the Pacific Northwest, we have forests that, because of the Northwest timber wars in the 1990s, are actually bursting with wood. Their forest management, their sustainable harvesting methods can be cultured through higher-value products like mass timber.
I made a decision fairly early on to engage with local suppliers. All of our projects have been sourced within the Cascadia biome, I’ll call it, which is from southern British Columbia down to southern Oregon, about a 500-mile radius. I intend to keep it that way. The pricing sometimes is a little higher, but the benefits of being able to source within a 400-to-500-mile radius are extraordinary, and to be able to go out to those factories and meet their owners — and oftentimes, they’re two, three, fourth-generation owners.
“The benefits of being able to source within a 400-to-500-mile radius are extraordinary”
They’re also highly entrepreneurial and taking big risks for their particular family-owned company. And they know their forests.
You design buildings, but you also helped update the model construction code, which means taller timber buildings are allowed in jurisdictions that adopt the new code.
The International Code Council had just come out, in 2016, with a call for architects who knew mass timber to sit on this code committee. I got a call from the American Institute of Architects. They said, “We’d really like you to apply.” I said, no, I’m not a code geek. They didn’t really want me for my code ability, which was very smart of them. They wanted me for my mass timber building experience. At that time I had built two [timber] projects in the West of the US. And that was about two more than almost anybody else at the time.
Out of that 18-person committee, six of them were fire [safety-focused] people, who were were terrified. They would bring you to tears, listening to them talk about how we were going to design the wooden high rises and they were all going to burn down. This was a real, obvious concern of theirs.
So to see all those 18 people, including myself, sit around the table and hold the dignity of the code front and center, that was a really interesting phenomenon to experience. And then we were able to collaborate over a two-and-a-half year period, including doing a year of fire tests, and they were more successful than anybody believed.
You really could try to burn this building down for four hours, without sprinklers, and it wouldn’t burn down. And then you could do it again, and it still wouldn’t burn down.
With the growth of interest in mass timber, what does the supply chain look like? Are there enough sawmills and specialty fabricators to meet the demand?
Today, the answer is probably no. But I also think it’s really changing very fast. And it’s been very dynamic. Ten years ago, when I started in earnest with getting bids for my house, we only had one factory west of the Mississippi, and another one east of the Mississippi. Now we have a lot more [timber] buildings, but we also have a lot more suppliers. And the forest capacity is there — and that’s a whole other question, is to continue to ensure that the wood is coming from sustainably harvested forests.
Is greenwashing a risk?
We’re trying to be really, really honest with ourselves about where the wood comes from, how it is harvested, the forest practices. And we’re trying to be as clear and as honest and as transparent about the lifecycle analysis of these buildings. Like the supply chain, it’s in a bit of a state of flux; we don’t have all the answers. We’re all learning and we’re continuing to research.
“The benefits of being able to source within a 400-to-500-mile radius are extraordinary”
You’re referring to methods of lifecycle analysis?
How you quantify the sustainable footprint of a building. I mean, it wasn’t that long ago that we thought a sustainable building was, you know, LEED Platinum with incredibly low operational carbon. Maybe five years ago, the industry as a whole figured out: Wait a minute, we’re spending a lot of carbon to make a lower-carbon building, right? That’s how fast the industry has been changing.
If you could look five years into the future, what do you think you would see with regard to mass timber in North America?
My hope is that we’re changing the 20th-century paradigm of construction. We are introducing a biophilic material, which has a much lower carbon footprint, into the building industry forever.
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