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American Society of Landscape Architects


November 2007 Issue

Above It All
A Seattle-based bank’s roof garden is a spectacular amenity for employees.

By Linda McIntyre

Above It All

The new headquarters of Washington Mutual Bank in Seattle was designed to be a great place to work. Primary among its many employee-friendly features is a roof garden, winner of a 2007 ASLA General Design Honor Award, designed by Vancouver landscape architecture firm Phillips Farevaag Smallenberg (PFS). 

This is an “intensive” rooftop garden, not a thin-profile “extensive” green roof planted with tough, low-maintenance plants such as sedum. The depth of planting areas ranges from 12 to 30 inches, and the plant list includes shore pines evocative of the Pacific Northwest; broadleaf evergreens such as ceanothus, azaleas, and boxwoods to provide structure, mass, and greenery during winter months; and hardy drought-tolerant species such as upright ornamental sedums ‘Ruby Glow’ and ‘Matrona,’ woolly thyme, and grasses.

With all of the current buzz about the environmental benefits of green roofs, do conventional roof gardens still add value? The landscape architects believe this roof garden provides some of the same services as more functional green roofs. “The roof garden provides some basic environmental benefits by absorbing reradiated heat from the building and reducing stormwater by storing it in the drainage layer of the roof and reabsorbing some rainfall in the planting profile,” says Joe Fry, PFS’s project manager. No data has been kept on any actual benefits, and there’s no system for capturing rainwater that falls on the building’s hard rooftop surfaces.

The garden was designed to be relatively low maintenance—“An irrigation system was provided,” says Fry, “but it remains to be seen whether it will be required as the plants mature and adjust to their environment” during Seattle’s dry summers. But it’s still more a roof garden than green roof, with all that implies, both positive (better access for staff and other visitors, a more diverse planting palette) and negative (more maintenance and resource intensive, fewer ecological benefits) (see “Shades of Green,” Landscape Architecture, October 2006).

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