Helping a Seattle street treat people and nature better

The Denny Triangle north of downtown Seattle was for years a nondescript collection of parking lots and cheap motels from the era of the Seattle Expo. “It hasn’t changed much in the last 60 years,” acknowledges Lyle Bicknell, urban designer in the Seattle Department of Planning and Development.

But new uses are starting to move into the 40- to 50-acre neighborhood as the City and developers begin to appreciate its potential. A major challenge has been what to do about the streets, which were built “atypically wide for Seattle,” Bicknell says. “There’s an opportunity to think differently about how we use the street. Streets are not just a sewer for cars any more. They’re a defining element for neighborhoods.”

The story of the Denny Triangle’s transformative first mixed-use development, on Taylor Avenue, is told in Heather Venhaus’s new book, Designing the Sustainable Site: Integrated Design Strategies for Small-Scale Sites and Residential Landscapes. The 256-page softcover ($65 from Wiley) explains how the predominantly residential project known as Taylor 28, developed by BRE Properties, changed one block of Taylor Avenue in ways that benefit both pedestrians and the natural environment.

“It’s the first link in a chain of connected streets,” Bicknell said of the block-long project when asked about it by Better! Cities & Towns.

The city, he said, wants to upgrade the neighborhood through “relatively high-density residential development paired with high-capacity transit.” A streetcar line that connects the neighborhood to the rapidly redeveloping South Lake Union area began operating in December 2007.

The Denny Triangle for decades was “painfully close to amenities,” but because of broad, busy traffic arteries, “it was difficult to get to them,” Bicknell explained. Now a deep-bore tunnel is being constructed to carry traffic that had used the heavily traveled Alaskan Way Viaduct. When the tunnel is complete, he said, “we will be able to reestablish and knit together the grid.”

The Internet retailer Amazon is seeking entitlements for development of three full blocks; Amazon has targeted each block for a 1-million sq. ft. office tower. The City requires retail on the ground floor, and the buildings will pay to support a significant volume of affordable housing, Bicknell added. Over all, the neighborhood is expected to get thousands of residential units.

A sustainable street

Venhaus, founding principal of Regenerative Environmental Design in Austin, Texas, describes the 197-unit Taylor 28 project as one that “sets a precedent for a new urban design standard”; it “transfers underutilized roadway into the public realm.”

The vehicular surface of Taylor Avenue was 56 feet wide, including two travel lanes and diagonal parking. Sidewalks on each side of the street were 18 feet wide. The project team—the Seattle firm Mithun was in charge of the architecture and landscape architecture—narrowed the asphalt-paved street by 20 feet. Two travel lanes remain, but the extensive angled parking was eliminated and a smaller quantity of parallel on-street parking was constructed.

The dramatically widened pedestrian zone has been interspersed with stormwater planters—containers that capture runoff, filter the pollutants, and prevent contaminated water from reaching Puget Sound. Rainwater runoff from Taylor 28’s plaza soaks into permeable paving and a series of urban rain gardens. Sediments and pollutants settle out and are held or treated by the soil, microorganisms, and vegetation.

Unlike some stormwater collection areas around the nation—which new urbanists have at times criticized for drabness or an inability to accommodate human activities—the stormwater planters on Taylor Avenue support trees, grasses, and perennial wildflowers, and enhance the streetscape. Structural soil beneath the streetscape increases the rooting area available to shade trees.

The project is designed to manage stormwater in downpours as severe as a 25-year storm. A 16,000-gallon rainwater cistern captures water for landscape irrigation and nonresidential toilet flushing. Altogether, a variety of techniques, including low-flow plumbing fixtures, have been estimated to reduce water consumption by 122,000 gallon a year.

Mithun says rich materials and curving forms have been used to draw pedestrians toward the building. With its built-in seating, the design creates small outdoor rooms for intimate gatherings, neighborhood dinners, and conversations, the architecture firm says.

Bicknell sees such high-quality outdoor spaces as offering a viable alternative to suburban living. “If you’re asking people to give up their back yards, you need to give them a great front yard,” he says.
The streetscape design concept has been approved by the City for the entirety of Taylor Avenue, which stretches several blocks north and south of Taylor 28. “These projects are done on a case-by-case, opportunistic basis,” depending on interest from developers, Bicknell notes. “We try to identify places that are open to redevelopment, and have plans in place. It’s a good model.”

The book

Venhaus’s book is carefully organized and offers clear, concise guidance on how to deal with sites in ways that uphold both livability and ecological functions. Designing the Sustainable Site ranges from big-picture explanations of current ecological thinking to detailed techniques that can be applied at the level of the individual site.

The text and a large array of color photos and drawings look at green roofs, green walls, living walls, permeable paving, rain gardens, sun-reflecting materials, urban heat islands, structural soils, local and indigenous landscape materials, flooding, water pollution, air pollution, invasive species, site design processes, and other topics.

Venhaus led the development of the Sustainable Sites Initiative: Guidelines and Performance Benchmarks 2009, which is described as the nation’s first rating system for landscapes.