The city of Seattle recently approved a proposed modification in building codes which would set a new bar for U.S. standards in urban development. Based on similar models in Sweden and Germany, the Green Factor is part of Seattle's plan to bring more greenery to the streets of commercial districts, and to compensate for the limitations urban density imposes on green space. The plan encourages a site-appropriate package of greening possibilities, including green roofs, interior green walls, exterior vertical landscaping, and rain gardens, which can help with building insulation, shading, air filtration, and stormwater runoff management. The city will offer incentives which will grant developers credit against open-space requirements when they install more compact or innovative landscape features, either on their site or in nearby public spaces, which improve environmental health and urban livability.

An article in the Seattle Post-Intelligencer reports that the proposal has raised some skepticism among builders and building owners who worry about things like rat-infestation in the thick vegetation of green roofing or walls, as well as the potential that mitigating runoff in such a rain-soaked region can't be done with these solutions alone. But designers have come a long way in creating effective and beautiful systems for architectural greenery. By looking at models in varying climates, these systems can be intelligently adapted to suit their local weather conditions.

To understand the thinking behind the new rules, consider the forests that occupied this land before they were cleared to make room for city development, suggested Steve Moddemeyer, a senior adviser with the city's Department of Planning and Development.

In such a forest, rainfall first hits the tallest trees, sticking to needles and bark. Then it might trickle down onto vine maples, still 15 feet or more above the ground. Next, it drips down onto salal, a leathery native shrub. From there, it drops onto ground-covering plants such as moss and kinnikinnick. Then, it drains its way through organic debris before reaching the soil. In a thick, old forest, the whole process can take 30 days.

In the city, it takes only a few minutes for rainfall hitting sidewalks, streets, parking lots and other impervious surfaces to pour into storm and sewer drains -- often bringing street pollutants in its wake.

A reduction in runoff reduces the associated costs of managing drainage systems, cleaning polluted groundwater and creeks, and dealing with street flooding. The savings permit the city to incentivize and facilitate more surface greening, and of course, the more developers choose to follow these new rules, the more beautiful Seattle will become, likely leading other cities to encourage similar practices.

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