Washington Revised Code Title 36. Counties § 36.70A.680. Accessory dwelling units--Local regulation

(1)(a) Cities and counties planning under this chapter must adopt or amend by ordinance, and incorporate into their development regulations, zoning regulations, and other official controls the requirements of this section and of RCW 36.70A.681, to take effect six months after the jurisdiction's next periodic comprehensive plan update required under RCW 36.70A.130.

(b) In any city or county that has not adopted or amended ordinances, regulations, or other official controls as required under this section, the requirements of this section and RCW 36.70A.681 supersede, preempt, and invalidate any conflicting local development regulations.

(a) Restricting the use of accessory dwelling units for short-term rentals;

(b) Applying public health, safety, building code, and environmental permitting requirements to an accessory dwelling unit that would be applicable to the principal unit, including regulations to protect ground and surface waters from on-site wastewater;

(c) Applying generally applicable development regulations to the construction of an accessory unit, except when the application of such regulations would be contrary to this section or to RCW 36.70A.681;

(d) Prohibiting the construction of accessory dwelling units on lots that are not connected to or served by public sewers; or

(e) Prohibiting or restricting the construction of accessory dwelling units in residential zones with a density of one dwelling unit per acre or less that are within areas designated as wetlands, fish and wildlife habitats, flood plains, or geologically hazardous areas.