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Jun 03, 2021

Evaluating the New Seattle Stormwater Code

Is your Seattle Development applying for a construction permit after July 1, 2021? Let Blueline help you evaluate the new stormwater code!

Blueline has been working closely with Seattle Public Utilities and other industry professionals to evaluate and provide relevant feedback regarding the stormwater code change being implemented this July in Seattle. We’ve listed some relevant changes below. We’d love to discuss your new project and how these code changes can fit with your design goals.

  • Stormwater, foundation drainage, and groundwater (only permanent) may need to find a new discharge location! This type of water discharge will no longer be allowed to discharge to a ‘formerly combined’ sewer main. Discharge to a combined main will be restricted unless the project meets certain exceptions. This change may impact your project, but there are ways to come up with a cost-effective solution.
  • Is there a ditch or culvert system fronting your project? Beware – a storm main extension may still be required!
  • A standard downstream analysis will be required by a professional for any new development.
  • Detention will now be triggered if your project adds 5,000 square feet of new hard surface. A quick area take off can let you know if you are triggering detention requirements with your proposed development.
  • Non-infiltrating bioretention planter sizing factors are reducing. Applying this requirement to your site can help you find out how much bioretention square footage can be reduced.

If you need help with your project or have more questions, please contact Project Manager, Kimberly McNabb. You can also visit SPU’s Revisions Page for the full list: Updating Stormwater Regulations – Project Documents – SDCI |