Published March 14, 2026

ADU Rules San Juan County, Lottery, Size, Permits

Accessory dwelling unit rules are specific in San Juan County. Start with current county code, then confirm details before finalizing design or budget.

Core ADU rules to confirm first

ADUs are accessory living areas on the same lot as a principal residence, with sleeping quarters, kitchen, and sanitation.
The living area cap is 1,000 square feet under SJCC 18.40.240(F)(1).
Detached ADUs outside urban growth areas and activity centers are subject to a county lottery process.
Detached ADUs permitted on or after June 29, 2007 cannot be used as vacation rentals.

Review the county ADU page and current code text directly before project decisions:San Juan County ADU information and SJCC 18.40.240 code text.

Lottery and permit planning

Detached ADU permits outside urban growth areas and activity centers are capped annually through the lottery framework. County timelines, fees, and application windows can change each year, so confirm current dates with San Juan County before preparing submittals.

For permit steps, start with county permit channels:SJC Permit Center and Applying for a Permit.

If your ADU scope includes electrical work, remember electrical permits are handled through Washington L&I, not county building permit channels.

Cross-checking future state law changes

Washington State ADU statutes can affect local implementation over time. For current county process, follow county guidance first, then track relevant RCW updates:RCW 36.70A.681.

If you are early in planning, combine this guide with licensing and permit basics before requesting bids.