Yakima, WA Accessory Structures: ADU Rules (2026)

Yakima's existing ADU framework sits in YMC 15.09.045 (Accessory Dwelling Units) under Chapter 15.09 Special Development Standards. The existing standards: (1) Form — the ADU may be attached to the primary residence, attached to or built above a detached garage, or be its own stand-alone structure; (2) Size — ADU floor area shall not exceed 1,000 sq ft; (3) Exterior Design — exterior walls must be similar in style, color, and building materials to the primary detached dwelling; (4) Setbacks — an attached ADU has the same setbacks as the primary structure; a detached or above-garage ADU has the same setbacks as an accessory structure (typically 5 ft side/rear from YMC 15.05 Table 5-1); (5) Parking — off-street parking shall be provided per YMC Chapter 15.06 for both the ADU and primary residence; (6) Density — a parcel/lot shall contain no more than one single-family residence and one ADU; (7) Prohibition — ADUs are not permitted on parcels containing a duplex, multifamily dwelling, or commercial/industrial structure. WA HB 1337 (2023), codified at RCW 36.70A.680, 36.70A.681, and 36.70A.696, materially changes this for Yakima. As a GMA-planning city with population over 25,000, Yakima must by mid-2025 (six months after its next periodic comprehensive plan update under RCW 36.70A.130): (a) allow at least two ADUs per single-family lot (one attached + one detached, or two attached, or two detached); (b) eliminate owner-occupancy requirements; (c) allow ADUs at least 1,000 sq ft in floor area; (d) permit ADU height up to at least the height of the primary structure or 24 ft, whichever is greater; (e) impose no off-street parking minimum for ADUs within 0.5 mile of a major transit stop; (f) impose no impact-fee multiplier above 50 percent of the comparable single-family impact fee. RCW 36.70A.680 also requires ADUs to be allowed on all lots that permit single-family residences. Yakima Planning is processing a code update to YMC 15.09.045 to bring it into HB 1337 compliance — until adopted, conflicts between YMC 15.09.045 and HB 1337 are resolved in favor of state law per RCW 36.70A.020. Separately, WA HB 1110 (2023), codified at RCW 36.70A.635, requires Yakima as a city over 75,000 population to permit duplexes, triplexes, and fourplexes in all single-family zones — providing an additional development pathway alongside the ADU rules. ADU construction requires building permits from the Yakima Code Administration Division under the 2018 Washington State Building Code (RCW 19.27 — based on 2018 IBC/IRC).