Accessory Structures in Walla Walla County, WA (2026)
5 rules for unincorporated Walla Walla County, Washington.
Verified from official government sources
ADU Rules
Unincorporated Walla Walla County allows one accessory dwelling unit per lot under WWCC 17.08.015: the primary home must be at least 800 square feet, the ADU is capped at 1,100 square feet or half the primary home's size, mobile homes and RVs cannot serve as ADUs, and the ADU must share at least four utilities or features with the main house.
Walla Walla County ADU Zoning Rules
Some RestrictionsWalla Walla County Code § 17.08.015(C)-(I)
C.The size of the primary residence must be at least eight hundred square feet to allow an accessory dwelling unit;D.The accessory dwelling unit, excluding any garage area and other nonliving areas, shall not exceed one thousand one hundred square feet, or fifty percent of the total square footage of the primary residence (excluding any garage area and other nonliving space), whichever is less;...
ADU Impact Fees
Walla Walla County charges $744 in Community Development planning fees to add an accessory dwelling unit in the unincorporated area, on top of the regular building permit fee scale. There is no separate GMA impact fee for ADUs. County code caps the unit at 1,100 square feet or half the primary home's floor area, whichever is smaller, and requires the owner to live on-site rent-free at least six months a year.
Walla Walla County ADU Permit Fee and Size Cap
Some RestrictionsWalla Walla County Code §§ 3.08.110, 15.04.031, 17.08.015
TYPE FEE Accessory Dwelling Unit $744.00 ... Any person who commences work on a building, structure, site grading, plumbing, mechanical system, gas line, or other activity prior to obtaining a permit required by this code shall be subject to an investigation fee. The investigation fee shall be equal to the permit fee set forth in Chapter 3.08, resulting in a double fee. ... "Accessory dwelling ...
ADU Owner Occupancy
In unincorporated Walla Walla County, an accessory dwelling unit is allowed only if either the primary residence or the ADU itself is occupied by a property owner for at least six months out of every year. The county's zoning code bars the owner from ever collecting rent on whichever unit serves as that owner-occupied home, a condition enforced by Community Development alongside the county's other accessory dwelling unit standards.
Walla Walla County ADU Owner-Occupancy Rule
Some RestrictionsWalla Walla County Code § 17.08.015(J)
17.08.015 - Accessory dwelling unit. "Accessory dwelling unit" means a dwelling unit within a primary residence or an accessory building for occupancy by a person or family for living and sleeping purposes, or for the temporary use of guests of the occupants of the premises. "Accessory dwelling unit" includes "guesthouse." Any accessory dwelling unit used as a bed and breakfast guesthouse shall...
ADU Rental Restrictions
Unincorporated Walla Walla County lets owners rent out an accessory dwelling unit once it meets the county's other ADU conditions: one extra off-street parking space, one ADU per lot, and in urban growth areas a ban on pairing the ADU with a family day care or home occupation on the same lot. WWCC 17.08.015(K) is the actual rental permission.
Walla Walla County ADU Rental Rules
Light RestrictionsWalla Walla County Code § 17.08.015(K)-(O)
K.An accessory dwelling unit may be rented.L.One parking space must be provided for the accessory dwelling unit in addition to the parking required for a one family dwelling unit;M.Accessory dwelling units are allowed only on a lot with a one family dwelling unit;N.Accessory dwelling units are allowed within or accessory to a one family dwelling unit; andO.An accessory dwelling unit in an urban...
Shed & Carport Rules
Walla Walla County lets a detached garage or similarly sized accessory building sit as close as five feet from a side or rear property line in unincorporated zones. WWCC § 17.18.020, development condition 7, requires the community development director to first confirm the structure sits entirely within the rear third of the lot and will not harm neighboring property before granting the reduced setback.
Accessory Building Setback Rule, Walla Walla
Some RestrictionsWalla Walla County Code § 17.18.020, condition 7
7. A side and/or rear yard setback may be reduced to five feet for a detached garage or similarly sized accessory building upon a determination by the director that: A. The detached garage or similarly sized accessory building will be located entirely within the rear one third of the lot; and B. Such detached garage or similarly sized accessory building will not be unduly detrimental to adjacen...
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