Skagit County, WA Accessory Structures: ADU Rules (2026)

106 defines an accessory dwelling unit as separate living quarters on the same lot as a primary residence, either detached or built into the main house, and it must independently provide for eating, sleeping, cooking, and sanitation. Countywide, a newly constructed ADU cannot exceed 1,200 square feet of floor area, not counting any garage space, and the combined primary residence and ADU(s) must provide three off-street parking spaces. An ADU built into the primary home cannot share interconnected interior spaces with the main unit, and neither a recreational vehicle nor a park model trailer qualifies as an ADU under this section.

Inside Skagit County's Urban Growth Areas, up to two ADUs are permitted per primary residence, but two units require connection to a public sewer system; only one is allowed if the property instead relies on an on-site septic system. UGA parcels also get relief provisions: a legal nonconforming structure that doesn't meet setbacks or lot coverage can be converted into an ADU, ADUs may be sited at lot lines abutting a public alley, and off-street parking is waived entirely if the site sits within a half mile walk of a major transit stop.

Outside the UGAs, in the county's rural zones, only one ADU per primary residence is allowed, it cannot be subdivided off from the primary unit's ownership unless the zoning allows it, and a detached ADU must be located within 150 feet of the primary residence unless a greater distance is needed to protect critical areas or natural resource lands, or existing development makes the 150-foot distance impossible. A primary dwelling containing an ADU is also limited to one obvious street-facing entrance, unless more than one entrance already existed before the current ADU ordinance was adopted.