Seattle, WA: Seattle Green Factor
Policy Title: Seattle Green Factor
Year Adopted: 2006, Expanded in 2009
City: Seattle, WA
Main Citation: Seattle Green Factor
Description:
Thoughtful and well-designed landscaping has the potential to improve the look of a neighborhood, support adjacent businesses, and decrease crime, all while providing ecosystem services such as reducing stormwater runoff, providing habitat, and mitigating urban heat island impacts. Modeled off of the 1997 Biotope Area Factor in Berlin, Germany, the Seattle Green Factor is a score-based code requirement that serves to increase the amount of and improves the quality of landscaping in new developments to maximize these positive benefits to the city.
The code requires that landscaping meets a minimum Green Factor Score and affects a number of land uses, not including neighborhood residential zones and some industrial and downtown zones. The score is calculated as follows:
Identify all proposed landscape elements, sorted into the following categories: planted areas, plants, green roofs, vegetated walls, permeable paving, structural soil, and bonuses.
Multiply the square feet, or equivalent square footage where applicable, of each landscape element by the multiplier provided for that element as detailed in the code.
Notably, the preservation of existing trees at least six inches in diameter at breast height is given the highest credit, with a multiplier of 1.0.
Add together all the products calculated to determine the Green Factor numerator.
Divide the Green Factor numerator by the lot area to determine the Green Factor score.
The score is roughly equivalent to the percent landscaped area. Thus, a score of 0.5 indicates 50% of a parcel being landscaped.
This system also creates two important incentives, rewarding points for landscaping visible from adjacent rights-of-way or public open space and maximizing credits for layering vegetation. The Green Factor should serve to increase higher-quality, better-integrated landscape design in the City, enhancing livability and sustainability.
Impact:
Seattle’s Urban Forestry Commission has found the Green Factor to be an ineffective tool for tree retention, as these requirements could be met with other landscaping measures. The organization Friends of Urban Forests has called this system “green washing,” as trees are still removed from land so it can be developed. The Green Factor cannot be an alternative to policies “that are intended to ensure the protection of a sufficient quantity of existing parks, natural habitats and other green open spaces.”
Additional Resources:
Seattle Code § 23.86.019, Table A
Green Factor Scoresheet and Worksheet