August 3, 2006

Green Factor would change urban landscape design

  • Proposed city program would require vegetation for new development in neighborhood commercial areas.

    Photo courtesy Michael Shopenn
    Avalon Bellevue’s courtyard has a traditional common area, with a small lawn and hardscape installed above structured parking.

    As awareness of the environmental impact of metropolitan areas grows, sustainability takes on a decidedly urban flavor. Regulators have responded with a variety of zoning code proposals for increased density, structured parking, pedestrian-friendly streetscapes and most recently, landscape requirements.

    Last month, the city’s Department of Planning and Development released a draft of the Seattle Green Factor program, which involves landscape requirements for new development in neighborhood commercial areas.

    Green Factor is based on European approaches to urban sustainability, and offers landscape strategies that encourage sustainability and increase green space in the city. Current requirements mandate a percentage of open space on a development site, but the result is not necessarily green or sustainable. If approved by the City Council, Green Factor would require that a variable portion of a parcel be vegetated.

    This variable would be defined by selecting from a list of possible options, ranging from trees, shrubs and groundcovers of differing sizes and soil depths to green roofs and water features. Each option is assigned a specific point value. The values range from a factor of 0.2 to a factor of 0.7. Lower values correspond to lawn and groundcovers, small plants and small-to-medium trees, while higher values are associated with large trees and shrubs, green roofs, vegetated walls and water features.

    The calculation uses a simple spreadsheet. The number of plants or the square footage is multiplied by its point factor. Increasing plants or square footage will accomplish the aggregate 0.3 green factor.

    At first glance, this seems fairly easy to achieve. The landscape strategies suggested are not unusual; green roofs and vertical vegetated walls are becoming more common. The Green Factor is a menu of green elements that offer a developer flexibility. But when we applied the Green Factor to a current GGLO project permitted under current open space requirements, it became apparent that achieving the Green Factor will do just what its authors hope: change the way we approach urban landscape architecture.

    Some case studies

    Photo courtesy GGLO
    A courtyard playground in Malmo, Sweden, has plantings and storm drainage features.

    The sample case is an approximately 14,000-square-foot, mixed-use urban infill project in the Capitol Hill commercial district. The open space and landscape area are on the second floor, at the residential level. The courtyard landscape has raised planter boxes with small trees, shrubs and groundcover plantings. Ground floor commercial uses have a pedestrian-friendly streetscape, with street trees, outdoor furniture and special paving. This project was granted a departure from the required 20 percent open space to 10 percent.

    According to the worksheet, the project’s 1,260 square feet of plantings and 21 trees garner less than a third of the vegetated square footage Seattle Green Factor would require. To see how this project could be designed differently to comply, we looked for other options with relatively high values that would suit our client’s budget and program.

    The project is planted with as many large trees and shrubs as the open space can support. Because of feasibility, maintenance and cost issues, avoiding permeable paving, vegetated walls or a water feature made sense. Inevitably, the green roof option became more and more appealing.

    Adding a green roof over the residential units put the tally over the 0.3 target with many obvious advantages. The project is pursuing LEED certification, and a green roof would help achieve that goal. Improved thermal comfort, lower utility bills and reduced storm water run-off are all long-term benefits of green roofs, which offset installation and maintenance expenses.

    A look at Portland

    Our experience in Portland, which is also aggressively implementing sustainable urban design, suggests that they, too, may be arriving at a similar outcome. Portland specifically encourages green roofs with a program established in 2001 for downtown districts that grants additional floor area ratio for a roof that has at least 60 percent green roof or roof garden. Getting more building height is a powerful incentive for developers who want to maximize their rental space.

    The Bureau of Environmental Services in Portland regulates green roofs, in conjunction with the Department of Planning, and they have stringent requirements. BES thoroughly reviews green roof and irrigation plans and specifications, as well as maintenance.

    GGLO is working on two projects with roof gardens/green roofs that are going through this process. Portland’s approach, though very focused on intensive green roofs, speaks to issues similar to those found in the Seattle Green Factor worksheet.

    For instance, all plants must be drought-tolerant. Plants will also be on a strict watering schedule during the first three years and an even stricter schedule after that — a low water regimen from May through October only. Irrigation is required and needs to be planned carefully, with each zone responding to varied micro-climatic elements and location. An efficient subsurface drip system with a low evaporation rate was the obvious answer. Seattle’s proposed Green Factor includes small but not insignificant bonuses for drought-tolerant plantings and high-efficiency irrigation.

    Though the plant selection criteria are not so specifically spelled out in terms of square footage, plants do need to cover submitted green roof areas within one year. This requirement echoes the Green Factor approach of maximizing square footage of vegetation.

    Both programs aim to make urban environments more sustainable and more aesthetically pleasing to pedestrians and users by making them more visibly green.

    Future projects

    Photo courtesy GGLO
    The Louisa, a mixed-use building in Portland’s Pearl District, has successfully combined green roofs with roof gardens.

    In Seattle, open space and landscape area are common departure requests from the current code. The Green Factor would almost certainly change that. By clearly distinguishing open space from vegetation factor, it places a strong emphasis on green features and elevates them beyond mere amenities into necessary urban attributes. In most neighborhood commercial zones, open space requirements would likely be reduced from 20 percent to 5 percent of the gross residential area.

    We can make no predictions about the ultimate outcome. Every urban site obviously has its own unique opportunities and constraints. The Green Factor is structured to offer a variety of options that promote green space suitable to every situation.

    What we can say is that in constrained spaces with limited budgets, our tendency would be to focus on green elements that offer the greatest value and benefit to the client while giving up the least floor area ratio.

    Green roofs and vertical green are two factors with a high point value (0.7) that seem to represent the most opportunity. Green roofs offer many additional benefits. Vertical green is a lower-cost option that would also use existing square footage and offers the benefit of greater visibility to pedestrians.

    Implementing the Green Factor might be tedious and spark its share of controversy, but the sustainable and aesthetic benefits are numerous. Overall, it would be advantageous for all parties, and represents one more step toward sustaining urban livability in Seattle.

    Marieke Lacasse, ASLA, and Shaney Clemmons are both LEED Accredited Professionals and part of the Landscape Architecture Group at GGLO.

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