Wildland Urban Interface (WUI) Code Updates


Wildland-Urban Interface Codes (WUIC or WUI) reduce wildfire risks to people and property. Changes to code have been approved at the state level that may impact construction in Snohomish County for structures that are not vested before October 29, 2023. (The initial implementation date was July 1, 2023. However, on May 24, 2023, the State Building Code Council voted to delay the implementation of the 2021 Washington State Building Codes under emergency rule for 120 days starting on June 30, 2023. Therefore, the new implementation date is October 29th.) 

You can learn about the WUI code on this informative StoryMap created by the Washington State Department of Natural Resources, which provides background and links to more information.  


The Washington State Legislature has adopted the 2021 International Code Council (ICC) codes. The Wildland-Urban Interface Code is part of this code. Beginning on October 29, 2023, projects not currently vested must meet these code requirements, which could have a significant impact on proposed construction.

The WUI code adds fire protection standards to all structures based on proximity to areas with "vegetative fuels" that can contribute to wildfires even if permits are not required. The WUI code specifies ignition-resistant construction requirements for buildings, decks, detached structures and other components to protect against fire ignition from embers.

What's New?

Determining whether a project will have to comply with requirements of the WUI code can be done by consulting the WA Department of Natural Resources Map (link) or by consulting the Snohomish County PDS Map Portal and navigating to the WUI layer. (Click here for instructions on how to do this). While complex in administration and application, there are some items that when incorporated into projects go a long way towards compliance with the WUI code. Some of those are outlined below for reference.

Ventilation openings such as crawlspace and attic openings shall not exceed 144 square inches per vent. Openings are to be protected with maximum 1/4" metal mesh or be designed and approved to prevent flame or embers from entering the structure. Attic ventilation openings are no longer permitted in eave overhangs of soffits.

Exterior wall construction options include non-combustible materials, ignition resistant materials, 1-hour rated, heavy timber, or fire-retardant treated materials.

Class A roofing and valley flashing, if applicable, shall be metal.

Deck material options include heavy timber construction or approved alternatives per WAC 51-55-0500 Section 501.6. Heavy Timber minimum sizes for posts (6" X 6"), beams (6" X 8") and joists/star stringers (4" X8"). Walking surface materials have specific construction requirements, and decks less than 48" above finished grade shall be enclosed with screen material from grade to the underside of joists.


Coming soon.



Q: What does 'vested' mean, and how do I know or make sure my project is vested by October 29, 2023?

  • A:  A project is deemed vested upon submittal of a complete permit application and required permit documents AND payment of application fees. This means that an applicant must have submitted a valid application and paid the applicable fees by October 28, 2023.  When an application is received, PDS staff review the application for completeness and then invoice the applicant to pay the fees.  Applicants should allow enough time for this process and therefore submit applications they want to vested well before October 28th. Submitting an application on October 28th may not result in vesting due to insufficient time for staff review and payment of fees.

Q: I can't figure out if my project will be subject to this change using the resources above. What do I do?