ADU rules in Pasco, WA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Pasco allows one attached or one detached ADU per residential parcel with a conforming single-family home (not in the RP zone). The ADU may be up to 1,000 sq ft or 55% of the main house, whichever is less, and up to 25 ft tall. No extra parking is required, but occupants must live in the ADU more than 180 days per year.
Under PMC Chapter 25.161, adopted by Ordinance 4575, the City of Pasco permits a maximum of one attached or one detached accessory dwelling unit (ADU) on each residential parcel that has a legally permitted, conforming single-family dwelling. ADUs are allowed in most residential zones but not the RP (Residential Park) District. The city's ADU Guide states the maximum size is 1,000 square feet or 55 percent of the main dwelling's total square footage, whichever is less, and the maximum building height is 25 feet or the height of the main dwelling, whichever is less. ADUs are exempt from residential density limits. The city does not require additional off-street parking. Occupancy is for long-term residential use only - occupants must live in the ADU more than 180 days per year (no short-term/vacation rentals). A detached ADU must sit at least 10 feet from the main dwelling and 6 feet from other structures, with its entrance at least 15 feet from the side property line; maximum rear-yard coverage is 60 percent. Washington's statewide ADU law, HB 1337 (RCW 36.70A.681), requires planning cities to allow at least two ADUs per single-family lot in urban growth areas, bars owner-occupancy mandates, prohibits size caps below 1,000 sq ft, bars height limits under 24 ft, and bars parking requirements within one-half mile of a major transit stop. Pasco must bring its code into compliance within six months of its periodic comprehensive-plan update (deadline December 31, 2026 for Franklin County under SB 5558), so confirm current standards with the Planning Division.
Building an ADU without permits, or one exceeding the size, height, setback, or coverage standards, can trigger code-enforcement action, stop-work orders, and required correction or removal. Using an ADU as a short-term/vacation rental violates the long-term occupancy requirement. Electrical and plumbing work requires separate permits.
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