Pasco, WA Accessory Structures: ADU Rules (2026)
ADU rules in Pasco, WA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- ADUs per parcel
- 1 attached or 1 detached, not both
- Maximum size
- 1,000 sq ft or 55% of primary home, whichever less
- Maximum height
- 25 ft or height of primary home, whichever less
- Detached separation
- 10 ft from principal dwelling, 6 ft from other accessory structures
- Occupancy rule
- Long-term only, over 180 days/year, no short-term rental
- Permit process
- Ministerial/administrative, no public hearing
Summary
Pasco allows one attached or one detached ADU on any residential lot with a legal single-family home, processed as a ministerial or administrative permit with no public hearing. Size is capped at 1,000 square feet or 55 percent of the primary home, whichever is less, with a 25-foot height limit.
Number of ADUs Per Parcel. A maximum of one attached or one detached ADU is permitted on residential parcels with legally permitted and conforming single-family dwellings; provided, that all the requirements of the PMC and applicable development regulations are met. ... Unit Size. The size of the ADUs shall not exceed 1,000 square feet or 55 percent of the total square footage of the primary residence or dwelling, whichever is less. Unit Height. The maximum height of the ADU shall be no taller than that of the principal dwelling or 25 feet, whichever is less.
Official source re-checked September 8, 2026: no newer edition of the code had been published (publisher’s edition: current through Ordinance 4837, passed May 4, 2026).
Full Breakdown
PMC 25.161.040(1) limits every parcel to "a maximum of one attached or one detached ADU," and PMC 25.161.020 permits ADUs in all residential zoning districts on parcels with a legally conforming single-family home. Applications go to the Department of Community and Economic Development and are processed ministerially or administratively without a public hearing unless the ADU is requested alongside a subdivision or short plat, in which case it moves through that Title 21 process instead (PMC 25.161.030). Size is capped at "1,000 square feet or 55 percent of the total square footage of the primary residence or dwelling, whichever is less," and height cannot exceed the principal dwelling or 25 feet, whichever is less (PMC 25.161.040(5)(b)-(c)).
A detached ADU must keep the underlying zone's side and rear setbacks, stay at least 10 feet from the principal dwelling, at least six feet from any nonhabitable structure like a shed or garage, and cover no more than 60 percent of the rear yard (PMC 25.161.040(5)(d)-(e)). Its main entrance must sit at least 15 feet from the side property line and cannot face a neighboring property (PMC 25.161.040(5)(f)). Occupancy is restricted to long-term residential use: PMC 25.161.040(3)(b) bars short-term or vacation rental use and requires occupants to reside more than 180 days per calendar year.
ADUs are exempt from the underlying zone's density standards entirely (25.161.040(2)) and from the general accessory-structure setback table in PMC 25.22.050, being governed by Chapter 25.161 instead.
Violations & Fines
Building more than one ADU per parcel, exceeding the 1,000-square-foot/55-percent size cap, or using an ADU for short-term or vacation rental in violation of the 180-day residency rule under PMC 25.161.040(3)(b) are reported to and enforced by the Pasco Code Enforcement Hearings Board (PMC 25.161.040(3)(c)). An ADU built without a permit is treated as prima facie evidence of a violation once the City shows by a preponderance of the evidence that it lacks one, rebuttable only by proof no permit was required when it was built (PMC 25.161.040(6)(f)(i)).
Frequently Asked Questions
How many ADUs can I build on one lot in Pasco?
How big can a Pasco ADU be?
Can I rent my Pasco ADU on Airbnb?
Sources & Official References
Other rules in Pasco
Compare Pasco to another location·View the Washington accessory structures overview
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