Accessory Structures in Lewis County, WA (2026)
4 rules for unincorporated Lewis County, Washington.
Verified from official government sources
ADU Rules
In unincorporated Lewis County, an accessory dwelling unit is capped at one per lot, two bedrooms, and 1,296 square feet under LCC § 17.102.050. It must share the principal structure's driveway access and meet IRC and L&I construction standards, plus water/septic setbacks under Chapters 8.40 and 8.55 LCC.
Lewis County ADU Rules
Some RestrictionsLewis County Code § 17.102.050
§ 17.102.050. Allowance of accessory dwelling units. (1) Accessory dwelling units shall meet the following requirements: (a) There shall be no more than one accessory dwelling unit per lot in conjunction with a single-family structure. (b) The accessory dwelling unit shall share the same primary access to a public right-of-way as the principal use. Looped driveways shall have two approved road ...
Shed & Carport Rules
A detached tool shed, playhouse or similar structure of 200 square feet or less doesn't need a building permit under Lewis County's amended IRC R105.2, but every accessory building still has to meet the county's side and back setbacks, and on a corner lot it can't sit closer than 15 feet to the street line.
Lewis County Shed Setback and Permit Rules
Some RestrictionsLewis County Code §§ 15.05.020(1)(b), 17.07.010, 17.142.030
IRC R105.2 Work exempt from permit (1) One story detached structures used as tool and storage sheds, playhouses and similar uses, provided that the floor area is not greater than 200 square feet. ... Each violation of the provisions of this title or the provisions of any regulation, order, permit or ruling promulgated pursuant thereto shall constitute a civil infraction. Infractions shall be pr...
Garage Conversions
Lewis County's Small Town UGA code lets a homeowner convert an existing garage into an accessory dwelling unit even if the conversion violates the property's setback or lot coverage standards, as long as the finished ADU meets every other applicable building and land use requirement.
Lewis County Garage-to-ADU Conversion Rule
Light RestrictionsLewis County Code § 17.17.130
(1) There shall be no more than two accessory dwelling units per lot in conjunction with a single-family structure. (2) A garage may be converted to an ADU, even if it violates existing requirements for setbacks or lot coverage. The converted ADU shall meet all other applicable laws and requirements.
Tiny Homes
Lewis County's zoning code defines a "tiny home" as a dwelling unit of 220 to 1,000 square feet with its own kitchen and bathroom, and names tiny homes as one of the structure types the county allows to operate as a short-term rental, subject to the same annual permit and occupancy rules as other rentals.
Tiny Home Rules in Lewis County
Some RestrictionsLewis County Code § 17.10.200; § 17.105.030(1)(a); § 17.105.040(1)-(2)
"Tiny home," also called an "efficient dwelling unit," means a dwelling unit having a total floor area of not less than 220 square feet and not more than 1,000 square feet and that contains a living space, a bathroom and kitchen facilities. ... The following may be permitted as short-term rentals: (a) Single-family residences, accessory dwelling units, duplexes, tiny homes and detached bedrooms...
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