Seattle's Green Factor, absorbing rainwater and softening the urban landscape

I sometimes hang out at the Rooflines blog hosted by the National Housing Institute, where a post by David Holtzman on green infrastructure caught my eye today.  It features an innovative program by the city of Seattle designed to bring more greenery to its business districts while absorbing stormwater runoff. 

As described on the city's website:

"A new landscaping requirement is helping create lush new plantings in neighborhoods throughout the city. Known as the Seattle Green Factor, this program is designed to improve the quantity and quality of planted areas while allowing greater flexibility for developers and designers to meet open space requirements. Currently, it applies to new development in commercial and neighborhood commercial zones outside of downtown, and it is proposed for multifamily residential zones and the South Downtown planning area."

Basically, a city ordinance requires the equivalent of 30% of a parcel in commercial zones to be vegetated through planting of layers of vegetation and larger trees in areas visible to the public.  The system's scorecard provides additional bonuses for rainwater harvesting and/or low water use plantings and encourages the use of larger trees, tree preservation, green roofs, green walls and water features.

What I especially like is that - as the illustration from the website, reproduced above, demonstrates - the requirements may be met without discouraging urban densities necessary to achieve smart growth goals.  As I posted a few days ago, these kinds of practices just make smart growth even smarter.  There's an excellent presentation and lots more on the city's Green Factor website.