A Love Affair with Wood Inspires One of the US's First CLT Houses
Shortly after graduating from architecture school, Susan Jones worked at a design firm in Vienna. She learned about mass timber or cross-laminated timber (CLT) from contacts there, first developed in Austria in the 1990s. Even after founding her firm in 2003, atelierjones LLC, in Seattle, her Austrian colleagues continued to send her information about CLT's growth in residential construction throughout Europe, including a catalog from an award program for single-family houses built with CLT in Austria.
To say Jones is enamored with CLT and its potential is an understatement. "I've been inspired by CLT," she explains. "The Pacific Northwest is a timber-rich part of the world, where old-growth forests have been managed for decades." As a Pacific Northwesterner, born and bred, she adds, "forests are a gigantic part of our natural and cultural landscape, which has made me think deeply about the value of wood."
"If we're using big pieces of timber in design and construction and not being smart about it, that's very limited thinking," she continues. "CLT and Pacific Northwest wood is a perfect marriage of technology and environmentalism in one product new to the US. It's a natural combination."
Jones has become a national leader in the mass-timber community. In 2016, she represented more almost 100,000 architects (on behalf of the American Institute of Architects) to successfully change American building codes to allow tall mass-timber buildings up to 18 stories in the US.
In 2018, she published Mass Timber | Design and Research. Her all-woman firm has designed a church and two modular CLT schools. The firm is currently working on an 8-story mass-timber workforce housing project, a prefabricated mass-timber workforce housing project, and a mass-timber prefabricated modular house, among other buildings.
Her first CLT project, however, was her own home. After purchasing a small triangular infill site in 2011, Jones says, "We took our time with the design." Built using CLT panels and clad in Shou sugi ban, the home also features a fresh, light, uncovered CLT interior.
An Urban Cabin
"So many of us in this region grew up with little cabins in the woods," Jones says. "I fondly remember my grandmother's cabin on Orcas Island. I really wanted this house to be an urban wooden cabin, so I felt like I was walking into the woods every day—to feel that sense of emotional release and relaxation I'd felt when we'd go to the cabin on Orcas. I wanted to replicate that in the city as an urban cabin. And I wanted to build extremely sustainably."
At the same time, Jones adds, "I realized the house could be a demonstration project. So few structures in the US at the time were being built with mass timber." Designing and building the home with CLT, she continues, "was a real opportunity to create something innovative with the knowledge I have as an architect. Moreover, the project would help people understand what mass timber really is."
CLT as Structure and Interior
Jones sited the 1,500-square-foot, three-sided home on a compact triangular lot across from an alley and parking lot. The second floor is cantilevered over a parking spot. Built to PassivHaus standards, the nearly raw interior (the walls have a light UV coating, the floors were left untreated) creates a visceral experience of nature. The abundant windows and skylights enhance the lightness of the wood with natural illumination.
The project required 184 trees, 67 CLT panels (from small-diameter spruce pine fir [SPF] trees), and twelve days to erect the panels. Structurlam fabricated the CNC-milled panels from rapidly renewable, sustainably harvested CSFI-certified spruce, pine, and fir. Jones's family planted 800 trees to act as an additional carbon sink.
What Efficient Design Features Did the CLT House Use?
Built with a super-insulated envelope, the home's walls are R-35, and the roof is R-49. The structure is wrapped in a Wrapshield vapor-permeable air barrier. Thick layers of Roxul rock wool are compressed by strapping installed with Heco Topix screws, which have a thread that reverses, so they insert a specific distance.
With its tightly sealed construction, the air-tight home achieves a low ACH or air changes per hour but, Jones says, "does not meet Passive House standards. While we weren't aiming for PassivHaus certification, the home was a City of Seattle Priority Green project." The home also has Euroclime triple-glazed windows, a heat recovery ventilation (HRV) system, is sited and wired for a solar array, and achieved a Built Green 5-Star rating.
Jones' home was the first CLT structure to be permitted in the City of Seattle. It's also one of the first in the US to use CLT as structure and finish material. As a result, the house has served as not only a demonstration project; but also a research vehicle for Jones' architectural firm. The project has also been shared with the CLT community locally and nationally, with policymakers and academicians, and with architecture and engineering communities worldwide.
A Singular Design
The home's spatially dynamic design reflects its triangular site. Jones planned views to be carefully screened or revealed through triangular windows. She also had technicians maximize CNC technology by cutting some interior panels or screened window walls to evoke pine knots.
Jones' home has a vertical, three-level central service core that channels utilities from the basement to the roof deck. The core is clad in plastic laminate, stainless steel, and quartz. Around the core, dramatic vertical spaces open up through the kitchen, staircase, and to the cedar roof deck with views of Lake Washington.
The house also has a rainwater cistern, "incredible roof planters we grow food in all year," lots of cross-ventilation, and a "super-efficient hot-water heater," Jones adds. A hydraulic-raised skylight to the roof deck is "a fantastic thermal night flush to let hot air out in the summer."
Looking Back
Jones has few regrets. "We're pretty happy with the house," she says. Still, she wishes she would have taken more time during the construction phase. "The first thing is not to build in the winter with CLT. I was rushing, and it wasn't any fun trying to protect the panels from rain." While the electrical and utility cabling works beautifully, "I would have brought more rigor to their placement and integration with the structure."
While she was inspired by Passive House detailing, "I now wish we would have tried harder to achieve certification. The mass timber was such a stretch for our brains. We didn't have the bandwidth to go for Passive House certification. Still, the modeling showed we're 38% better than Washington State energy codes." Taping the outside of the CLT panel joints, which would have required additional time and money, "would have been a simple thing to do nonetheless, and brought us closer to the Passive House standard."
What she's accomplished, in part, however, is demonstrating how "CLT promotes timber as a building material that, if harvested responsibly, can elevate the Cascadia region as an innovative culture of highly sustainable strategies," Jones says, pointing to how, in her own home, she transformed the CLT panels into beautiful, light-filled space.
"Waking up being surrounded by wood, watching how the light falls on the wood, feeling the wood under my bare feet," she adds, "imbues us with a deep and abiding respect for our natural environment and its exquisite beauty every day."
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Camille LeFevre
Camille LeFevre is an architecture and design writer based in the Twin Cities.