Accessory Structures in Snohomish County, WA (2026)
4 county-level rules, plus city-specific rules for 4 cities in Snohomish County, Washington.
Verified from official government sources
ADU Rules
SCC 30.28.010 caps ADU floor area at 1,200 square feet and lets urban single-family lots host up to two accessory units, in any mix of attached or detached, since the county's 2025 rule changes. Rural lots get only one, and detached units are barred on R-5 lots under five acres.
Accessory Dwelling Unit Rules in Snohomish County
Some RestrictionsSCC 30.28.010
Accessory dwelling units are allowed under SCC 30.22.100, 30.22.110, 30.22.120, and this section. (1) General standards. All accessory dwelling units shall comply with the following standards: ... (e) The floor area of an accessory dwelling unit shall not exceed 1,200 square feet. Floor areas shall be exclusive of garages, porches, unheated storage areas, and unfinished basements... (2) Urban z...
Shed & Carport Rules
In unincorporated Snohomish County a carport is an accessory structure used to cover vehicles or boats. Detached garages and storage structures over 2,400 square feet must sit at least 15 feet from external property lines; over 4,000 square feet, at least 20 feet.
Carport and detached garage rules
Some RestrictionsSCC 30.23.110
Detached accessory or non-accessory storage structures and private garages with building footprints over 2,400 square feet must be at least 15 feet from any external property line; provided, that parcels abutting open space tracts shall have a five-foot setback from the open space. Storage structures and private garages over 4,000 square feet in size must be set back at least 20 feet from any e...
Garage Conversions
Converting a garage into habitable space in unincorporated Snohomish County is treated as creating an accessory dwelling unit and must meet SCC 30.28.010 ADU standards, including the 1,200-square-foot cap, water/sewer capacity, and off-street parking.
Converting a garage into a living unit
Some RestrictionsSCC 30.28.010
Accessory dwelling units are permitted uses in the urban zones pursuant to SCC 30.22.100 on lots with a single family, single family attached, or duplex dwelling. The floor area of an accessory dwelling unit shall not exceed 1,200 square feet.
Tiny Homes
In unincorporated Snohomish County a recreational vehicle cannot be a primary residence. A tiny house counts as a dwelling only if built on a foundation, permitted, and connected to water and sewer; a tiny house on wheels is regulated as an RV.
Tiny homes and RVs as dwellings
Some RestrictionsSCC 30.91R.050
"Recreational vehicle (RV)" means a travel trailer, motor home, truck camper, or camping trailer that is permanently designed and used as temporary living quarters, is either self-propelled or mounted on or drawn by another vehicle, is transient, and is not immobilized or permanently affixed to a mobile home lot. (Added by Amended Ord. 02-064, Dec. 9, 2002, Eff date Feb. 1, 2003). 30.91R.060...
Accessory Structures by City in Snohomish County
4 cities in Snohomish County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
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