WA SB5470

Counties may permit detached accessory dwelling units (DADUs) outside urban growth areas if they adopt development regulations meeting specified requirements and track permits annually

DADUs are limited to one per parcel, maximum 1,296 square feet, must be within 150 feet of the principal unit, share the same driveway, and cannot be built on designated forestland

Water supply requirements include compliance with RCW 19.27.097, metering of all dwelling unit withdrawals, adherence to domestic use limitations in RCW 90.44.050, and documentation that septic/sewage systems can handle additional demand

If a DADU is used as a short-term rental (fewer than 30 consecutive nights), the primary unit must be owner-occupied

Counties must update comprehensive land use plans to account for completed and projected DADU development, with plan amendments for DADUs limited to once every five years