Tiny home rules in Pasco, WA — covering tiny houses on wheels (THOWs), park model RVs, and tiny home on foundation builds — determine where they are legal and how they get permitted.
Pasco has no separate tiny-home ordinance. A permanent tiny house on a foundation is treated as an ADU, capped at 1,000 sq ft or 55% of the main house, whichever is less. A tiny home on wheels (titled as a motor vehicle) and RVs/motorhomes are not recognized as ADUs and cannot serve as permanent dwellings.
Pasco does not publish a tiny-home-specific code. A permanent, site-built tiny house on a foundation that has independent sleeping, cooking, and sanitation facilities is regulated as an accessory dwelling unit (ADU) under PMC Chapter 25.161 (Ordinance 4575), capped at 1,000 square feet or 55 percent of the main dwelling's total square footage, whichever is less, with a height limit of 25 feet or the height of the main house, whichever is less. The city's ADU Guide is explicit on movable structures: 'RVs or Motorhomes are not considered ADUs under the Pasco Municipal Code,' and 'Tiny homes, if they are on wheels (a home built on a trailer titled as a motor vehicle) are also not ADUs.' That means a tiny house on wheels cannot be used as a permanent residence the way a foundation-built ADU can. A 'casita' can qualify as an ADU if it is independent of the main home and has kitchen facilities. Pasco currently allows one attached or one detached ADU per conforming single-family parcel, exempt from residential density limits, with no additional off-street parking required and long-term (180+ days/year) occupancy. Washington's HB 1337 (RCW 36.70A.681) requires planning cities to allow at least two ADUs of at least 1,000 sq ft per single-family lot in urban growth areas and bars owner-occupancy mandates; Pasco must conform by six months after its periodic plan update (Franklin County deadline December 31, 2026). Confirm classification and building-code requirements with the Pasco Permit Center.
Placing or occupying a tiny house that does not meet ADU and building-code standards, or living in a tiny house on wheels, RV, or motorhome as a permanent residence on a residential lot, can trigger code-enforcement action, fines, and required removal or correction.
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