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

• 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.

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).

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).

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.

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.

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. Not sure your parcel qualifies? See will your lot qualify for a DADU, what a DADU costs, how an ADU changes your property taxes, the Seattle permit process, and prefab vs site-built — or get a free site evaluation and we'll map your lot against the new rules.