Accessory Structures in Washington (2026)

Washington HB 1337 (RCW 36.70A.681) requires cities and counties to allow two ADUs per lot in urban growth areas…

Auburn allows two ADUs per residential lot outright in any residential zone that permits single-unit detached or middle…

Bellingham allows up to two accessory dwelling units per lot, capping each ADU at 1,000 square feet and detached units…

In the urban growth area you may build up to two accessory dwelling units per legal lot, each capped at 1,000 sq ft (up…

CCC § 18.10.585 lets unincorporated Cowlitz County property owners build one ADU, up to 1,200 square feet and 35 feet…

Edmonds allows a detached single-family home to have up to two accessory dwelling units under ECDC 16.20.060, capping…

Everett requires accessory dwelling units to meet the same setbacks as the main house, and its NR-C zone allows up to…

Federal Way allows up to two accessory dwelling units per single-family lot under FWRC 19.200.180, each capped at 1,000…

Franklin County allows one attached accessory dwelling unit per single-family home, capped at 800 square feet and 40…

In unincorporated Grant County, a second dwelling is allowed as an accessory to an existing single-family home, but the…

Kennewick allows two accessory dwelling units per lot in every residential zone, each capped at 1,100 square feet and…

Kent allows up to two accessory dwelling units per single-family lot, attached or detached, capped at 1,000 square feet…

In unincorporated King County, one Accessory Dwelling Unit is permitted per primary detached dwelling or townhouse…

Kirkland allows up to two accessory dwelling units per single-family lot, attached or detached, each capped at 1,200…

In unincorporated Kitsap County, a detached accessory dwelling unit built outside an urban growth area cannot exceed…

Lakewood, Washington allows up to two accessory dwelling units on any lot with a detached single-family home, duplex…

Lynnwood defines an accessory dwelling unit (ADU) as 1,000 square feet or less, either attached (AADU) or detached…

Marysville allows two accessory dwelling units per single-family lot with no owner-occupancy requirement, a change…

Pasco allows one attached or one detached ADU on any residential lot with a legal single-family home, processed as a…

Port Townsend allows up to two accessory dwelling units per single-family lot, each capped at 1,000 square feet, but…

Puyallup permits up to two accessory dwelling units per RS-zone lot that meets the underlying zone's minimum lot area…

Renton allows up to two ADUs per legal lot in the RC, R-1, R-4, R-6, R-8, R-10 and R-14 zones, attached or detached…

Within Sammamish's shoreline jurisdiction, SMC 25.07.080(7) allows only one accessory dwelling unit per primary single…

Skagit County Code § 14.18.106 caps a newly built accessory dwelling unit at 1,200 square feet, excluding garage area…

SCC 30.28.010 caps ADU floor area at 1,200 square feet and lets urban single-family lots host up to two accessory…

Spokane County allows one accessory dwelling unit (ADU) per single-family lot. Detached ADUs are capped at 800 sq ft on…

Spokane Valley allows one accessory dwelling unit per lot, attached or detached, under SVMC § 19.40.030. The ADU cannot…

Tacoma allows two accessory dwelling units per residential lot, each capped at 1,000 square feet of habitable area…

Thurston County caps accessory dwelling units at 850 square feet and allows only one ADU per lot with a single-family…

Whatcom County lets an accessory dwelling unit go on most residential and rural lots under WCC § 20.80.910, but the…

Yakima allows one accessory dwelling unit per single-family lot as a permitted use, capped at 1,000 square feet, with…

Washington's HB 1337 (RCW 36.70A.681) requires Benton County to allow at least two accessory dwelling units on…

Unincorporated Pierce County allows accessory dwelling units under PCC 18A.37.120. Two ADUs are permitted per lot…

Washington's HB 1337 (RCW 36.70A.681) requires Yakima County to allow at least two accessory dwelling units on lots…

Everett cuts its parks impact fee in half when a homeowner adds one or two accessory dwelling units to a lot that keeps…

Federal Way caps both transportation and park impact fees for accessory dwelling units at 50 percent of what a detached…

Kent exempts a homeowner's first accessory dwelling unit from the school impact fee entirely, treating it as part of…

Kirkland caps the transportation impact fee on a new accessory dwelling unit at fifty percent of the fee that would…

In unincorporated Kitsap County, road, park and school impact fees on an accessory dwelling unit cannot exceed fifty…

Lynnwood charges a park impact fee on every new accessory dwelling unit because the city's Table 3.104.030 fee schedule…

Pierce County caps traffic impact fees on accessory dwelling units at half the rate charged for the primary house…

Bellingham waives its multimodal transportation impact fee for ADUs built inside an existing single-family home or…

Unincorporated King County exempts accessory dwelling units from school impact fees under County Code § 21A.43.070.A.9…

Marysville exempts accessory structures and city-approved accessory dwelling units from its park, recreation, open…

Port Townsend exempts permitted accessory dwelling units from system development charges for water and sewer…

In unincorporated Skagit County, accessory dwelling units are exempt from every impact fee the county charges new…

Spokane Valley requires the titleholder of an ADU property to live in either the primary home or the ADU as a permanent…

Franklin County requires one of the two dwellings on a lot with an attached accessory apartment to be owner-occupied…

Outside an urban growth area, a detached accessory dwelling unit on unincorporated Kitsap County land is only legal if…

Outside Whatcom County's urban growth areas, and inside the Lake Whatcom Watershed Overlay and several rural districts…

Pasco does not require owner-occupancy to build an accessory dwelling unit, but it offers owner-occupancy as one path…

Bellingham does not require owner-occupancy to build or rent an ADU -- state law (HB 1337) bars that -- but an…

Kent does not require an owner-occupancy covenant for accessory dwelling units. KCC 15.08.350(B)(9) states a covenant…

Marysville imposes no owner-occupancy requirement on the principal home or an accessory dwelling unit -- the standards…

Port Townsend prohibits both the main house and any accessory dwelling unit from operating as a short-term rental once…

Bellingham allows short-term rentals in attached ADUs citywide but bars them in detached ADUs on residential-single…

Franklin County bars renting out rooms for lodging in a single-family home that already has an accessory dwelling unit…

In unincorporated Grant County, an accessory dwelling unit must be occupied as a permanent residence and cannot be…

Marysville's accessory dwelling unit code flatly bars using an ADU as a short-term rental, defined as lodging offered…

Pasco requires accessory dwelling units to be occupied on a long-term residential basis only. PMC 25.161.040(3)(b) bars…

An ADU in Yakima can be rented out short-term, but only if it also satisfies the city's separate short-term rental…

A storage shed in a required side or rear yard needs discretionary Process III approval in Federal Way, capped at eight…

Auburn lets you skip a building permit for a one-story detached tool or storage shed only if its floor area stays at or…

Bellingham caps detached accessory buildings like sheds and garages at 800 square feet and one story (12 feet), and…

In the Community Center Residential District, Benton County caps a parcel's total lot coverage at 40 percent and holds…

Carports and detached garages are accessory buildings under CCC 40.260.010. In R1 residential zones they cannot exceed…

A detached storage shed or playhouse in unincorporated Cowlitz County does not need a building permit if it is one…

Edmonds caps accessory building height at 15 feet and lets small accessory structures under 600 square feet reduce…

Everett treats a carport as an accessory building. Its footprint is capped at the smallest of 15% of the lot, 3,000…

Franklin County limits tent or canvas-covered storage sheds to 480 square feet in urban growth area residential zones…

In unincorporated Grant County, storage sheds, workshops, garages and barns are listed as permitted residential…

In Kennewick's R and HMU districts, detached sheds and accessory buildings must sit at least 5 feet from side and rear…

Kent lets homeowners build a shed or other accessory building anywhere on the lot that meets the principal building's…

In unincorporated King County, one-story tool sheds and playhouses under 200 square feet skip a building permit if the…

Kirkland caps detached accessory structures like sheds, garages and barns at 1,200 square feet, plus 10 percent of any…

Lakewood, Washington caps residential accessory buildings at 24 feet in height under LMC 18A.40.110(B)(9)(a). A small…

Lynnwood splits residential accessory buildings into Type 1 (one per unit, 64 square feet, 8-foot height limit, 1-foot…

Marysville caps residential accessory structures at 80 percent of the primary home's footprint on lots under an acre…

In Pasco's R-15 low density district, storage buildings are capped at 480 square feet total and 15 feet in height, with…

A shed, garage, greenhouse, or storage building in unincorporated Pierce County can go up to 576 square feet without a…

Port Townsend lets accessory structures under 120 square feet and 10 feet tall skip the standard rear setback, as long…

On a Puyallup RS-zoned lot up to four acres, only one detached accessory building over 200 square feet is allowed…

Renton limits detached accessory buildings like sheds and garages to two structures of 720 square feet each (or one at…

SMC 23.44.090(G) lets garages and carports sit in a required setback under specific conditions: a front-setback garage…

In unincorporated Snohomish County a carport is an accessory structure used to cover vehicles or boats. Detached…

In unincorporated Spokane County, a one-story detached storage shed under 200 sq ft needs no building permit, but must…

A shed in Spokane Valley needs at least five feet of clearance from the rear and side property lines and cannot sit in…

Tacoma caps accessory buildings like sheds at 1,000 square feet, or 15% of lot area, and requires they sit behind the…

In Thurston County's high-density residential zoning, a one-story accessory building under 200 square feet that's…

A backyard shed in unincorporated Whatcom County skips the building permit only if its footprint stays at or under 200…

Sammamish lets homeowners skip a building permit for a small tool or storage shed under SMC 16.20.200(2)(a): tool…

Skagit County Code § 14.18.104 lists a storage shed, workshop, garage or barn as an allowed 'miscellaneous residential…

Yakima lets homeowners build a detached storage shed up to 200 square feet without a building permit under its…

A one-story detached shed of 200 square feet or less needs no building permit in unincorporated Yakima County under the…

Auburn lets homeowners convert garage space into an accessory dwelling unit, but ACC 18.32.010(E)(3) requires the…

Bellingham lets homeowners convert an existing detached garage into an accessory dwelling unit even if the garage…

Clark County lets you convert an existing garage into an accessory dwelling unit, including a garage within…

In unincorporated Grant County, converting a detached garage into an accessory dwelling unit is allowed and must meet…

Kent lets homeowners convert an existing garage into an accessory dwelling unit even if the garage does not meet…

Converting a detached garage into an accessory dwelling unit in Kirkland is exempt from the zone's current setback and…

Outside an urban growth area, unincorporated Kitsap County lets a homeowner convert an existing detached garage into an…

Lakewood, Washington lets a homeowner convert an existing, legally built detached garage or accessory building into an…

Converting a garage into living space in unincorporated Pierce County requires a building permit, and creating an…

Puyallup lets homeowners convert a detached garage into living space by turning it into an accessory dwelling unit…

Converting a garage into habitable space in unincorporated Snohomish County is treated as creating an accessory…

Converting a garage or attached space into living quarters is treated as creating an accessory dwelling unit or added…

Tacoma allows homeowners to convert an existing garage or other accessory structure into a legal dwelling unit without…

Thurston County lets homeowners turn an existing garage or other internal space into an accessory dwelling unit under…

Inside a Whatcom County urban growth area, WCC § 20.80.910(2)(c)(iii) lets an existing detached garage, barn or other…

Marysville lets an existing detached garage convert to an accessory dwelling unit even if it doesn't meet current…

Washington allows tiny houses on permanent foundations under IRC Appendix Q (adopted in the state building code) for…

Everett bans new manufactured home, mobile home, RV park, and tiny home communities citywide. A tiny house is allowed…

Bellingham's building code locally adopts IRC Appendix Q, the tiny-house construction standard, giving builders a legal…

Washington defines a tiny house as a dwelling that may be built on wheels and is no larger than 400 sq ft, excluding…

In unincorporated Franklin County, leasing an individual parcel for a tiny house or tiny home with wheels (as defined…

Marysville allows up to two accessory dwelling units per lot under state-mandated ADU rules, but a detached ADU can't…

Unincorporated Pierce County treats a tiny home under 400 square feet on a permanent foundation as a residence…

Port Townsend permits tiny houses on wheels as accessory dwelling units in R-I, R-II, and R-III zones, subject to Type…

Seattle allows tiny houses on permanent foundations as Detached Accessory Dwelling Units (DADUs) under SMC 23.42.022…

In unincorporated Snohomish County a recreational vehicle cannot be a primary residence. A tiny house counts as a…

Tacoma normally requires manufactured homes built as two sections at least 12 by 36 feet each, but structures meeting…

Whatcom County recognizes four kinds of tiny home under WCC § 20.97.200: a site-built unit on a permanent foundation…

A tiny home on a permanent foundation is a dwelling in unincorporated Yakima County and may use IRC Appendix Q, while a…

In unincorporated Grant County, tiny homes are expressly allowed as accessory dwelling units alongside manufactured…