Stormwater Code and Manual Update 2026 - Project Documents

Project Documents

• Current Stormwater Code and Associated Director's Rules

Stormwater Code Ordinance Public Review Draft – March 2026

The following table outlines the summary of changes made to the Stormwater Code.

• Summary of Changes / Response to Comments to Stormwater Code (March 2026)

Public Review Draft (March 2026) for the 2026 City of Seattle Stormwater Code update.

• Draft Stormwater Code Ordinance*  

* This reference draft of the Stormwater Code ordinance is provided to support the review of the Stormwater Manual March 2026 Public Review Draft. The official copy of the Stormwater Code ordinance is anticipated to be published on April 6 and will be posted to the City Council calendar website.

Draft Director’s Rule Public Review Draft (Stormwater Manual) – March 2026

The following table outlines the summary of changes made to the Stormwater Manual for the Directors’ Rule Public Review Draft.

• Summary of Changes / Response to Comments to Stormwater Manual (March 2026)

Director's Rule Public Review Draft (March 2026) documents for the 2026 City of Seattle Stormwater Code and Stormwater Manual update:

• Draft Stormwater Manual Figure Revisions
• Draft Stormwater Manual
  • 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 – Plant and Tree List  

SEPA Determination of Non-Significance (DNS)

Seattle Public Utilities has conducted a State Environmental Protection Act (SEPA) environmental review of the City of Seattle’s proposed 2021 Stormwater Code and Rule Update and issued a Determination of Non-Significance (DNS). This proposal would amend the City of Seattle’s Stormwater Code and associated Directors’ Rule. 

• Stormwater Code SEPA Environmental Checklist 
• Stormwater Code Determination of Non-Significance (DNS) 

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 - updated 1/20/26)
• 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