By Mark Crawford
Seattle’s 120,000-square-foot “Stone34” building isn’t just pleasing to the eye – it’s also about as green as green can be. Thanks to the use of a variety of sustainable building materials, including exterior precast concrete panels, the U.S. Green Building Council certified Stone34 as LEED Platinum earlier this year.
The five-story, urban mixed-use building blends sustainable design with the elements of two eclectic neighborhoods. Stone34 serves as a visible beacon for an energetic community, acting as a trailhead for the neighborhood.
Developed and constructed by Skanska, Stone34 became the first project to use Seattle’s Living Building Pilot Program, which requires exceptional performance for water and energy resources along with social goals that far exceed criteria for LEED certification. These goals include adhering to market-rate pricing, achieving 75% reductions in energy and water use, and creating a community hub on the popular Burke-Gilman Trail.
The building’s design provides 8,500 square feet of open area at street level, providing ample public space to support the outflow of retail on three sides of the structure. The upper four floors contain office space. Attractive, two-tone precast exterior panels also help reflect heat. A grand exterior stairwell, clad in energy-efficient glass, moves the ground-floor activity up the building.
“ celebrates the act of taking the stairs and creating a close relationship between the tenant and the community,” said Wendy Pautz, partner with LMN Architects, the architectural firm for the project. “The office floors are highly visible to the street, with a digitally-modeled glazing pattern that balances daylight, views, glare and heat gain considerations.”
The social aspect of the street plaza continues upward by way of two terraces and a rooftop deck, creating continuous connections with the outdoors and the public. Green walls call attention to the building’s sustainable design while also providing habitat for birds and insects.
In 2014, Brooks Sports moved its global headquarters into Stone34, occupying more than 70% of the space.
Adding value with precast
Precast played a crucial role in Stone34 meeting its LEED Platinum standards and its ongoing Living Building Pilot Program commitments. Olympian Precast in Redmond, Wash., manufactured the architectural precast components for the project. These included precast exterior panels, integrally colored precast stair treads and landings for the main staircase, and precast planters that help make the roof deck an attractive gathering place for local residents.
Designers selected precast for the building’s exterior for several reasons. Use of precast concrete panels in conjunction with a dual sealant system and careful detailing eliminated the need for exterior sheathing and a separate water and air barrier assembly, which reduced building costs. Going with precast also reduced the number of materials used in the wall assembly. This resulted in fewer trips to the project site. In addition, waste reduction and recycling were more efficient because both occurred at the precast plant instead of on site.
“Precast was part of an energy-efficient wall system that facilitated use of a continuous air barrier and insulation,” said John Mrozek, an LMN architect who worked on the project. “Because precast concrete systems require a limited number of points of connection to the structure, minimizing thermal bridges through the assembly is greatly simplified.”
The unique location of the project resulted in a formal massing solution that integrated folded planes of glazing and precast concrete panels in response to the irregular urban street grid.
“The construction of the concrete panels produced well-crafted obtuse angles that resolved one geometry to the next,” Mrozek added.
The design intent for the precast concrete wall panels was to achieve a uniform, light color. Careful consideration was given to the type of aggregate and sand color used to consistently distribute an even color across the face of the panel and achieve the desired aesthetic. For contrast, charcoal-colored panels were used at the base of the building.
In addition to the exterior precast panels, the main stairway in Stone34 was built with precast stair treads. “A dark charcoal color was used with a smooth form finish, except that the front of the tread had a sandblasted nosing pattern for both visual and tactile difference at the tread nose,” said Kevin Jewell, project manager for precast manufacturer Olympian Precast.
The lighter exterior precast consisted of white cement, a blend of two sands and pigment. Charcoal panels used Type-III gray cement with black pigment. Both precast colors were acid etch finished. Jewell noted that Skanska was initially concerned about the environmental impacts of acid etching.
“I explained that all of our etching work is done in a contained area, with the acid and residue collected and pumped to a treatment tank,” he said. “The liquid is treated to pH neutral and then released to sanitary sewer. All this work is done under a permit from the Washington State Department of Ecology. After review, Skanska agreed that acid etch was the best finish for the project.”
Mrozek added that working closely with the precaster led to success.
“We worked collaboratively with Olympian Precast to achieve a solution that provided the desired aesthetic, longevity and technical resolution required for the project,” he said.
Almost all the concrete materials – including the aggregates, gray cement, reinforcing steel and most miscellaneous iron connections – were mined or processed within 300 miles of the construction site, which helped with the LEED scoring. Reinforcing Nucor steel is certified as 99.4% recycled content, with a mix of 82.5% post-consumer and 16.9% pre-consumer, post-industrial.
LEEDing the Way
Stone34’s success will go a long way toward convincing skeptical developers that this kind of sustainable LEED project, with its extra community commitments, can be a win/win for the developer, builder, tenants and local residents. It can also be profitable – in December 2014, Skanska sold the complex for $70 million. Precast concrete components are an essential part of the building design that contribute to its energy efficiency, cost efficiency and good looks.
Stone34 was named Office Development of the Year by the Washington Chapter of the Commercial Real Estate Development Association in 2014. This recognition reflects the growing interest in developing flexible green design standards to meet or exceed LEED and community standards for sustainable design, and that these goals are achievable and deliver important benefits to both the community and the environment.
Mark Crawford is a Madison, Wis.-based freelance writer who specializes in science, technology and manufacturing.