Thurston County directs staff to draft detached ADU cap of 50 with annual review

Thurston County commissioners on Dec. 16 directed staff to draft language that would cap permitted detached accessory dwelling units (ADUs) at 50 per year and create a standing annual review to monitor effects and recommend changes.

The motion, moved by a commissioner who introduced the proposal and seconded during the agenda-setting work session, instructs staff to prepare draft amendment language for the detached ADU section that would establish a cap of 50 and an annual reporting process. Chair Plaid Magsruh called the vote; multiple commissioners voiced "aye" and Commissioner Emily Klaus confirmed a "Yes" vote. A speaker announced the motion passes.

Supporters said the cap is intended as a tracking threshold tied to a new permit-review process inside the Community Planning and Economic Development (CPED) docket. "If we get to that cap within a year ... it would trigger our CPED department to come and sit with the Board of County Commissioners and say, hey, these ADU numbers are at their cap," one staff member said, describing how staff would return with data. CPED Director Ashley Araya described the standing permit-review docket as a flexible space to "load whatever you want on that train car" so the department can report emerging issues to the board and the planning commission.

Commissioners acknowledged the number 50 is provisional. "We in a meeting this morning ... it really is just arbitrary," a speaker said when asked whether the cap is metric-based. County staff and commissioners stressed the cap is paired with an annual review so the board can respond if demand is higher or lower than expected.

During discussion a commissioner asserted there have been "hundreds and hundreds illegally done" ADUs in the county and said the policy aims to capture that activity and guide safer, code-compliant construction. Staff also noted that, historically, the county has recorded under 20 permitted detached ADUs in the last five years, making 50 a conservative trigger to prompt review rather than an immediate restriction on supply.

According to staff, the draft language will be returned to the board and, if adopted, the annual review will include data on permit counts, development footprint (impervious surface coverage), and how standards are being applied. The board did not adopt the ordinance at this session; it directed staff to prepare the draft amendment for future formal consideration.

Next steps: staff will draft the amendment language for the detached ADU rules, incorporate the annual permit-review reporting structure the CPED director has built, and return to the board with the proposed ordinance language and recommended monitoring metrics.