Stormwater Code and Manual Update 2026 - Project Documents

Project Documents

• Current Stormwater Code and Associated Director's Rules

2nd Public Review Draft – January 2026  

The following table outlines the summary of changes made to the Stormwater Code and Manual for the second public draft.

• Summary of Changes to Stormwater Code & Manual (January 2026) 

Second public review (January 7 – February 9, 2026) draft documents for the 2026 City of Seattle Stormwater Code and Stormwater Manual update.

• Draft Stormwater Code Ordinance (January 2026)
• Draft Stormwater Manual Figure Revisions (January 2026)
• Draft Stormwater Manual (January 2026, unless noted otherwise)
  • 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 – On-site Stormwater List 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* – Plant and Tree List

*Note that the 1st Draft Appendix J titled “Contaminated Sites” has been deferred. Appendix J is now titled “Plant and Tree List.” 

1st Public Review Draft – July/August 2025

The following documents table outlines the summary of changes we  made to the code and manual for the first public review period (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)

First public review (July 8 – August 15, 2025) draft documents for the 2026 City of Seattle Stormwater Code and Stormwater Manual update.

• 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 – On-site Stormwater List 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
  • (still under development)Appendix K – Plant and Tree list