Code-Required Projects

The City of Seattle Stormwater Code requires construction projects to manage stormwater from project sites before it enters the City’s system. Compliance with the Stormwater Code reduces, slows and cleans runoff that eventually ends up in our waterways.
What is the purpose of Stormwater Code?

The purpose of this regulation is to protect life, property, and surface waters from harm caused by stormwater runoff. Seattle has had a municipal Stormwater Code in place since 1979 and adopted the current Code in 2016. The city must also comply with state and federal law, including the Clean Water Act.

Our city’s current Stormwater Code includes requirements for pollution prevention on existing sites and construction sites.

Stormwater Code projects are required when public or private land is redeveloped. The Municipal Stormwater Code defines the project requirements, and projects are developed and funded by the developer. The developer may be a private entity or a public agency, such as Seattle Department of Transportation. Roughly one percent of Seattle’s land is redeveloped every year, according to the Department of Planning and Development.

For development or redevelopment of roads, trails and sidewalks, single-family residential, and all other parcel-based projects, the current Stormwater Code includes requirements for flow control, water quality treatment, and on-site stormwater management. On-site stormwater management includes the GSI practices and the flow control and water quality treatment requirements state that GSI be implemented to the maximum extent feasible to meet the requirement.