Yakima, WA Accessory Structures: Tiny Homes (2026)

Yakima regulates tiny homes through the same framework as other residential and accessory structures. A tiny home built on a permanent foundation falls under the 2018 Washington State Building Code (RCW 19.27 + WAC 51-50 + WAC 51-51, which adopts the 2018 IRC including Appendix Q Tiny Houses). Appendix Q allows tiny houses (400 sq ft or less, excluding lofts) to use reduced ceiling heights (6'-8" in habitable rooms, 6'-4" in bathrooms), ladder or alternating-tread-device access to lofts, smaller stair geometry (winders allowed, headroom reduced to 6'-2"), and smaller egress window minimums (5.0 sq ft minimum opening for grade-level egress from sleeping lofts). Site-built or HUD-Code tiny homes on a permanent foundation may be: (1) the primary single-family dwelling — must meet the underlying Yakima zone's minimum lot area, lot width, setbacks, and dimensional standards under YMC 15.03 and YMC 15.05 Table 5-1 (SR generally requires larger lots with 20-25 ft front and 5-10 ft side setbacks; R-1 single-family 6,000-7,200 sq ft typical lot minimum with 20 ft front / 5-10 ft side / 15-20 ft rear setbacks; R-2 and R-3 have similar single-family lot mins with adjusted setbacks; exact values per Table 5-1); or (2) an Accessory Dwelling Unit under YMC 15.09.045 — 1,000 sq ft cap (raised for HB 1337 compliance), matching exterior, accessory-structure setbacks (5 ft side/rear). WA HB 1337 (RCW 36.70A.680) requires Yakima to allow at least two ADUs per single-family lot — meaning tiny-house ADUs are explicitly enabled. Tiny homes on wheels (THOWs) registered as travel trailers, park-model RVs, or recreational vehicles with WA Department of Licensing are NOT compliant with RCW 19.27 as permanent dwellings and cannot serve as a primary or accessory residence in any Yakima residential zone — YMC defines a dwelling unit as a structure designed for human occupancy with permanent provisions for living, sleeping, eating, cooking, and sanitation. RV park placement is governed separately by YMC Title 15 and RCW 59.20 (Mobile Home Landlord-Tenant Act). Manufactured (HUD-Code) tiny homes follow WAC 296-150M (WA manufactured home regulation by Labor & Industries) and may be placed in residential zones that permit manufactured homes per YMC 15.04 Table 4-1; designated manufactured housing communities follow YMC 15.03 (Mobile Home Park zone where applicable). WA HB 1110 (RCW 36.70A.635) middle-housing rules separately allow duplex/triplex/fourplex configurations that can include tiny-house-scale units on single-family lots in Yakima (>75K population).