Key Distinction: Long-Term vs Short-Term Rentals
HB 1337 eliminated owner-occupancy requirements and opened ADUs to long-term rentals. But it specifically does NOT prohibit local restrictions on short-term rentals (stays under 30 days). Seattle regulates STRs through its own license and primary-residence rules.
If you're considering building an ADU as an Airbnb or vacation rental, the rules depend on your city's short-term rental ordinance — not the state ADU law. In Seattle, that means a license and primary-residence requirements. Here's what applies.
Seattle STR Rules
Seattle has a formal short-term rental regulatory framework. The core rules:
- A Seattle short-term rental license is required to operate any rental under 30 days. (Seattle Ordinance 125490)
- Whole-home STRs are limited to the operator's primary residence (operator-hosted) — you generally cannot run a whole-home STR at a property you don't live in. (SMC 6.600)
- An ADU can be used as an STR, but the host must be a resident of either the primary home OR the ADU on the property. (SMC 6.600)
- Platforms (Airbnb, VRBO) must verify a valid license before listing — unlicensed listings are removed. (Seattle STR regulations)
- The annual STR operator license fee is approximately $75 per year. (Seattle FAS)
Contact: Seattle Department of Finance and Administrative Services (FAS) STR program.
What This Means for ADUs Specifically
Because Seattle's whole-home STR rules are tied to the operator's primary residence, an ADU can usually be a short-term rental — as long as the host actually lives on the property, in either the main house or the ADU.
This makes the classic owner-occupied setup viable: live in the main home, Airbnb the backyard cottage. What is harder is running an ADU as an STR on a property where nobody lives — that conflicts with the primary-residence rule even though HB 1337 lifted the owner-occupancy mandate for long-term renting.
Long-Term Rental: Always Allowed
While short-term rental rules are restrictive, long-term rentals (30+ day leases) are always allowed for ADUs in Seattle and King County, with no owner-occupancy required. This is protected by state law.
Long-Term Rental
- Protected by HB 1337
- No owner-occupancy required
- Steady monthly income
- Lower management overhead
Short-Term Rental
- NOT protected by HB 1337
- Requires a Seattle STR license
- Primary-residence rules apply
- Rules can change
Unincorporated King County
STR rules differ for properties in unincorporated King County — they are not subject to Seattle's ordinance. The county has its own regulatory approach, and rules can vary from the city's primary-residence model.
If your property is outside city limits, verify current short-term rental rules directly with King County DPER before planning an STR.
Our Recommendation
Build for long-term rental as your baseline plan. Seattle's rental market is among the strongest in the country — with a deep tech workforce, major hospitals, and two universities, demand for quality long-term rentals stays high.
If you plan to live on-site, an STR can be a great fit under Seattle's primary-residence rules. But don't build your entire financial plan around STR income that depends on continued residency and a license that could change. The most resilient ADU investment also works as a long-term rental.
Typical long-term ADU rental income in Seattle: $1,800-$2,600/month.
Ready to explore your options? Get a free feasibility study to see what's possible on your property, or let our permit team handle the paperwork.
Key Legal Sources
- Seattle STR Ordinance 125490 / SMC 6.600: seattle.gov
- HB 1337 (RCW 36.70A.680) — preserves local STR authority: app.leg.wa.gov
Last updated: March 2026. Not legal advice. STR regulations change frequently — verify current rules with Seattle FAS or King County DPER.
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