New Washington ADU Laws (2026): What Seattle & Tacoma Homeowners Can Now Build

Washington's ADU rules just got even friendlier: 2 ADUs per lot, no owner-occupancy, condo sales allowed — and new 2026 rural ADU rights. What it means for your property.

**Quick answer.** Washington is now one of the most ADU-friendly states in the country. Under **HB 1337**, every city in an urban growth area must allow **two ADUs per residential lot**, cannot require you to live on the property, cannot force street improvements, and cannot block selling an ADU as a condominium. And as of **June 11, 2026**, new law **HB 1345** opens a path for detached ADUs on **rural parcels outside urban growth areas** in counties that opt in. Here's what each change means for your lot.

Key facts

- **2 ADUs per lot** (attached, detached, or both — including two DADUs in Seattle) is now a statewide right in urban growth areas. - **No owner-occupancy requirement** — you can rent out both the main house and the ADU. - Cities **cannot cap ADU size below 1,000 sq ft** and must allow at least **24 ft of height** — two-story DADUs are in. - **ADUs can be sold as condominium units** — cities can't prohibit it (condo recording requirements still apply). - **Parking:** none can be required within a half mile of major transit; elsewhere it's capped at 1 space on smaller lots. - **NEW June 11, 2026 (HB 1345):** counties may allow **one detached ADU per rural parcel** outside urban growth areas — county opt-in, water-supply rules apply. - **Bonus:** Washington offers a **3-year property tax exemption** for qualifying remodels that add an ADU.

What HB 1337 locked in for city lots

If your property is in **Seattle, Tacoma, Bellevue, Renton, Kent, Puyallup**, or almost any incorporated Puget Sound city, state law now guarantees: two ADUs per lot; no owner-occupancy strings; no forced street improvements as a permit condition; design standards no stricter than the main house; and no size cap below 1,000 sq ft. Cities keep authority over the things that make sense locally — building codes, sewer connection, and short-term-rental limits (Seattle still requires an STR license tied to your primary residence).

The 2026 headline: rural ADUs (HB 1345)

Signed **March 27, 2026** and effective **June 11, 2026**, HB 1345 lets counties planning under the Growth Management Act allow **one detached ADU per rural parcel** outside urban growth boundaries. Participation is **voluntary per county** and **water-supply requirements** apply — so if you own rural acreage in Pierce or King County, the first call is the county planning department (we can make that call with you).

Selling an ADU separately: real, but not simple

State law bars cities from prohibiting the sale of an ADU as a **condominium unit**. That's a genuine exit strategy — build a DADU, condo-ize, sell it separately — but the condominium creation and recording process has real legal steps and costs. Worth designing for from day one if separate sale is your goal.

What it means city by city

**Seattle** consolidated its ADU code in mid-2025: two ADUs per lot (including two DADUs), DADUs up to 1,000 sq ft or 60% of the main home, no parking required, and the **ADUniverse** portal of pre-approved DADU plans that can cut review to a few weeks. Note: SDCI permit fees rose about **18% for 2026**, so budgets should reflect current fee schedules.

**Tacoma** allows two attached and/or detached ADUs up to 1,000 sq ft with no off-street parking — and with more generous lot sizes than Seattle, it's one of the best DADU markets in the state.

Pre-approved plan programs also run in **Kirkland, Renton, and Olympia**, with **Bellevue** developing one.

What hasn't changed

You still need permits, inspections, and a certificate of occupancy. Sewer capacity, setbacks (typically **5 ft rear/side** for DADUs in Seattle), and Washington's strict energy code all still apply — and older HOA covenants recorded before **July 23, 2023** may still restrict ADUs, so check your CC&Rs. The laws made ADUs a right; they didn't make them automatic. See our guides on [what a DADU costs](/blog/adu-cost-seattle-2026), the [Seattle permit process](/blog/dadu-permit-king-county), and [prefab vs site-built](/blog/prefab-vs-site-built-adu-seattle-tacoma) — or get a free site evaluation and we'll map your lot against the new rules.

FAQ

How many ADUs can I build on my lot in Washington?

In urban growth areas, at least two — attached, detached, or a combination. Seattle explicitly allows two detached units. Rural parcels may qualify for one detached ADU starting June 11, 2026 if the county opts in.

Do I have to live on the property to rent out my ADU?

No. HB 1337 eliminated owner-occupancy requirements — you can rent both the main home and the ADU long term. Short-term rentals remain separately regulated by cities.

Can I sell my ADU separately from my house?

Yes, as a condominium unit — cities cannot prohibit it. The condo creation and recording process involves real legal steps, so plan for it early if separate sale is your goal.

What's new in 2026?

HB 1345 (effective June 11, 2026) creates a county opt-in path for one detached ADU per rural parcel outside urban growth areas, plus water-supply conditions. Check your county's status.

Do the new laws waive permits?

No. Zoning, building codes, energy code, sewer requirements, and inspections all still apply — the laws remove local barriers, not the permitting process.

Washington's 2026 ADU laws hand Puget Sound homeowners more building rights than ever — but the difference between 'allowed' and 'built' is still a real permit set and a real contractor. Book a free site evaluation with NW ADU Builders and we'll map your lot against HB 1337, HB 1345, and your city's 2026 code, then quote a fixed-price design-permit-build path.