Stormwater Code and Manual Update 2026 - Project Documents

Project Documents

• Current Stormwater Code and Associated Director's Rules

The following document outlines the summary of changes we made to the code and manual for the first public review period that was July 8 – August 15, 2025.

• Summary of Changes to Stormwater Code & Manual  (July 2025) (Revised September 2025 with initial responses to public comments July 2025)

These are the draft documents for the 2026 City of Seattle Stormwater Code and Stormwater Manual update. The public review for these draft documents was July 8 - August 15, 2025

• Draft Stormwater Code Ordinance (July 2025)
• Draft Stormwater Manual Figure Revisions (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