This bill adds a new section to chapter 36.70A RCW and amends RCW 36.70A.696 to allow counties that are required or choose to plan under chapter 36.70A to permit detached accessory dwelling units (DADUs) outside urban growth areas only if counties adopt specific development regulations. The bill supplies definitions for accessory dwelling unit (attached and detached), dwelling unit, gross floor area, owner, principal unit, major transit stop, and short-term rental, and applies new limits and requirements to DADU development. Substantive legal changes include numeric and siting limits (no more than one accessory dwelling unit per parcel; DADU gross floor area capped at what could be authorized for an attached ADU expansion and no more than 1,296 square feet; DADUs must be sited within 150 feet of the principal unit; DADUs not allowed on nonconforming lots under one acre), water and septic requirements (metering of water withdrawals by each dwelling unit, combined withdrawals limited by RCW 90.44.050, applicants must document septic capacity or mitigation), and other controls (shared driveway, prohibition on subdividing to avoid limits). The bill creates enforcement and penalty rules and procedures: a voluntary compliance process that applies at least a double permit fee penalty when used; civil infractions of at least $1,000 for unpermitted construction with removal or remedy requirements; at least a triple permit fee penalty if an unpermitted ADU remains and meets regulations; and a three-year prohibition on permits for new accessory dwelling units for owners who did not seek voluntary compliance. It also requires counties to track and annually report the number of completed DADU permits to an unspecified department, update comprehensive plans at the next required review to account for completed and projected DADUs over a 20-year planning period, limit related plan amendments to no more than once every five years, and limit the share of rural population targets allocated to DADUs (no more than 10% for rural counties under RCW 43.160.020 and no more than 7% for non-rural counties). Agencies and groups affected include counties planning under chapter 36.70A, county code compliance programs, property owners and permit applicants, the Department of Ecology (for groundwater mitigation), and an unnamed state department that must receive annual DADU reports. The document does not identify which department receives reports, does not state an effective date for the new section, does not define the referenced "normal permit fee," and does not include the full existing text of the amended RCW or broader state implementation details.

If enacted, counties that plan under state law could allow detached accessory dwelling units in rural areas but only under tight technical and siting limits: one ADU per parcel, a size cap (no more than 1,296 sq ft), must sit close to the main house (within 150 feet), and cannot be placed on undersized nonconforming lots under one acre. Property owners seeking DADUs will need to show water use is metered and within state domestic withdrawal limits, prove septic systems can handle extra demand, and follow new enforcement rules that include doubled or tripled permit penalties, a minimum $1,000 civil infraction for unpermitted construction, and a three-year ban on new ADU permits for owners who skip voluntary compliance and are cited. Counties will face new planning and administrative work: adopting detailed development regulations, running tougher code enforcement, tracking and reporting annually to a state department (unnamed in the text), and updating comprehensive plans to account for DADUs with limits on how often those updates can be changed. This likely raises county staff time and enforcement costs and makes adding rural DADUs harder and more legally risky for homeowners; it also caps how much of a county’s rural population growth may be met by DADUs (10% for rural counties, 7% for nonrural). The bill text leaves unclear which state department receives reports, the effective date, and what the “normal permit fee” is, which could affect timing and cost estimates.