Stormwater Code and Manual Update 2026 - Project Documents

Project Documents

• Current Stormwater Code and Associated Director's Rules

The following documents outline the summary of changes we made to the code and manual.

• Summary of Changes to Stormwater Code & Manual (July 2025)

Draft documents for the 2026 City of Seattle Stormwater Code 

• Draft Stormwater Code Ordinance (July 2025)
• Draft Stormwater Manual (July 2025)
  • Volume 1 – Project Minimum Requirements
  • Volume 2 – Construction Stormwater Control
  • Volume 3 – Project Stormwater Control
  • Volume 4 – Source Control
  • Volume 5 – Enforcement
  • Appendix A – Definitions 
  • Appendix B – Additional Submittal Requirements
  • Appendix C – Onsite Stormwater Management BMP Infeasibility Criteria
  • Appendix D – Subsurface Investigation and Infiltration Testing for Infiltration BMPs
  • Appendix E – Additional Stormwater Design Requirements
  • Appendix F – Hydrologic Analysis and Design
  • Appendix G – Stormwater Control Operations and Maintenance Requirements
  • Appendix H – Financial Feasibility Documentation for Vegetated Roofs and Rainwater Harvesting
  • Appendix I - Landscape Management Plans and Integrated Pest Management 
  • Appendix J – Contaminated Sites
  • Appendix K – Plant and Tree list