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

015 governs accessory dwelling units (ADUs) built outside an urban growth area (UGA), which covers most of the county's unincorporated rural land, since county zoning reaches only unincorporated Kitsap and not Bremerton, Port Orchard, Poulsbo or Bainbridge Island. A detached ADU outside a UGA is capped at 900 square feet or 50 percent of the primary residence's habitable area, whichever is smaller, measured by interior dimensions. It must sit within 150 feet of the primary residence or be a conversion of an existing detached structure such as a garage, and it must be designed to match the primary home's appearance.

Only one ADU is allowed per lot, either attached or detached, never both together, and the property owner must occupy either the primary residence or the ADU. All zone setbacks apply, mobile homes and recreational vehicles can never serve as an ADU, and the unit must share the same street-side entrance as the primary house while adding an off-street parking space. Attached ADUs outside a UGA are capped at 50 percent of the primary home's habitable area and are barred where a detached ADU already exists.

010 sets a denser standard: up to two ADUs, attached or detached, per lot; a 1,000-square-foot size cap that the community development director may waive to match the primary home's footage if the ADU sits entirely on one floor; and a requirement for urban-level sanitary sewer service rather than septic. 04 once the owner documents continuous tax history and due diligence at purchase.