Seattle DADU Requirements: Your 2025 Guide to Zoning, Permitting, and New Laws
- Greg Brown
- Sep 11
- 3 min read
Seattle DADU requirements 2025 – contemporary backyard cottage and city zoning plan overlay.
What you'll discover in this article:
Planning to build a backyard cottage in Seattle? Understanding the latest DADU (Detached Accessory Dwelling Unit) requirements is crucial—especially with major ADU law changes taking effect in 2025. This definitive guide will cover Seattle DADU zoning, lot size, setbacks, height limits, parking, and the impact of Washington’s HB 1337. Learn the steps, avoid common pitfalls, and see how Apex DADU can streamline your path from idea to occupancy in the Seattle area.
Seattle DADU Zoning and Lot Requirements for 2025
Seattle DADUs must comply with updated setback (distance from property line), height, and lot coverage restrictions. In 2025, Seattle is raising height limits for backyard cottages in most zones—making it easier to include a loft or 2-story unit. Most DADUs must be set back at least 5 feet from side/rear property lines and are subject to overall lot coverage maximums. Generally, you can build up to 1,000 square feet per DADU in Neighborhood Residential zones. Always check the latest SDCI guidelines for your unique situation.
Setbacks, Height Limits, and DADU Size
Seattle DADUs must comply with updated setback (distance from property line), height, and lot coverage restrictions. In 2025, Seattle is raising height limits for backyard cottages in most zones—making it easier to include a loft or 2-story unit. Most DADUs must be set back at least 5 feet from side/rear property lines and are subject to overall lot coverage maximums. Generally, you can build up to 1,000 square feet per DADU in Neighborhood Residential zones. Always check the latest SDCI guidelines for your unique situation.
Parking, Owner-Occupancy, and Recent Law Changes (HB 1337)
Thanks to HB 1337, Seattle homeowners no longer need to provide dedicated off-street parking for their DADU if the site is near frequent public transit. The state law eliminated owner-occupancy rules for ADUs and reduced parking requirements across King County. Nearly any Seattle lot with appropriate space and access now qualifies for up to two DADUs, making backyard cottages more achievable citywide.
Permitting Process and Pre-Approved DADU Plans
Seattle’s Department of Construction & Inspections (SDCI) is updating its code to comply with HB 1337. The city's gallery of pre-approved DADU plans can dramatically streamline your project. If you choose a pre-approved plan, your permit timeline may drop to as little as 2–6 weeks—versus months for a fully custom design. Apex can help you select the best option for speed and flexibility.
Tips for Navigating Seattle DADU Requirements in 2025
Review the Seattle Municipal Code and SDCI’s ADU resources for up-to-date standards.
Request a feasibility study to ensure your lot supports one or two DADUs (Apex offers this with every consultation).
Leverage pre-approved plans for faster permits, or work with Apex DADU for tailored designs.
Watch for local updates: As each city in King County adopts new rules, details can vary.
Consider remaining code, stormwater, and permit fees—even with relaxed zoning, compliance is essential.
“Seattle’s updated ADU rules raise height limits, reduce setback requirements, and allow lots to support larger backyard cottages—making it structurally and legally easier for homeowners across Neighborhood Residential zones to build DADUs of up to 1,000 square feet without compromising neighborhood character.”
-Seattle Department of Construction & Inspections (SDCI)
Why Apex DADU is Your Seattle DADU Compliance Partner
Apex DADU keeps up to the minute on every law, zoning change, and permitting nuance in Seattle and King County. We’ll conduct a comprehensive feasibility check, recommend the fastest path (pre-approved vs. custom), guide your permit process, and ensure your project is 100% compliant, beautiful, and built to last.
FAQ: Seattle DADU Requirements in 2025
Q: How many DADUs can I build on my Seattle property in 2025?
You can build two ADUs per lot—either two detached cottages, or one attached and one detached.
Q: What are the new setback and height requirements?
Most DADUs must be at least 5 feet from side/rear lines. Height limits are increasing—check SDCI’s latest rules for details.
Q: Do I need to live on the property to build a DADU in Seattle?
No. HB 1337 and recent city updates have removed all owner-occupancy requirements.
Q: Is parking required for DADUs near transit?
Not if your lot is near frequent public transit. HB 1337 eliminates parking minimums in these areas.
Q: How do I get started with a DADU project?
Book a consultation with Apex DADU—we’ll run a feasibility check, explain your options, and handle the entire process for you.
Unlock Your Property’s Potential—Start with a Free Consultation
Seattle’s new DADU requirements make building a backyard cottage easier, faster, and more rewarding.
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