1. (1) For the purposes of this section, the definitions established in RCW 36.70A.696 apply.

2. (2) Requirements: Within urban growth areas, counties and cities:

   1. (a) Must allow at least two accessory dwelling units on all lots that allow for single-family homes in the following configurations:

      1. (i) One attached accessory dwelling unit and one detached accessory dwelling unit;
      2. (ii) Two attached accessory dwelling units;
      3. (iii) Two detached accessory dwelling units, which may be comprised of either one or two detached structures;
      4. (iv) Must allow accessory dwelling units to be converted from existing structures including, but not limited to, detached garages, even if they violate current code requirements for setbacks or lot coverage;
   2. (b) Must allow accessory dwelling units on any lot that meets the minimum lot size required for the principal unit;
   3. (c) May not establish a maximum gross floor area requirement for accessory dwelling units that is less than 1,000 square feet;
   4. (d) May not assess impact fees on the construction of accessory dwelling units that are greater than 50 percent of the impact fees that would be imposed on a principal unit;
   5. (e) May not require the owner of a lot on which there is an accessory dwelling unit to reside in or occupy the accessory dwelling unit or another housing unit on the same lot;
   6. (f) May not establish roof height limits on an accessory dwelling unit of less than 24 feet, unless the height limitation that applies to the principal unit is less than 24 feet, in which case a county or city may not impose roof height limitation on accessory dwelling units that is less than the height limitation that applies to the principal unit;
   7. (g) May not impose setback requirements, yard coverage limits, tree retention mandates, restrictions on entry door locations, aesthetic requirements, or requirements for design review for accessory dwelling units that are more restrictive than those for the principal unit;
   8. (h) Must allow detached accessory dwelling units to be sited at a lot line if the lot line abuts a public alley, unless the county or city routinely plows snow on the public alley;
   9. (i) May not prohibit the sale or other conveyance of a condominium unit independently of a principal unit solely on the grounds that the condominium unit was originally built as an accessory dwelling unit;
   10. (j) May not require public street improvements as a condition of permitting accessory dwelling units;
   11. (k) Must align parking with the requirements of WAC 365-196-875.

3. (3) Restrictions on ADUs.

   1. (a) Counties and cities are not required or authorized to allow the construction of an accessory dwelling unit in a location where development is restricted under other laws, rules, such as home ownership association rules, or ordinances. They may apply appropriate development regulations to the construction of an accessory unit;
   2. (b) Counties and cities may apply public health, safety, building code, and environmental permitting requirements to an accessory dwelling unit that would be applicable to the principal unit;
   3. (c) Counties and cities may apply regulations to protect ground and surface waters from on-site wastewater; as such, the construction of accessory dwelling units may be prohibited on lots that are not connected to or served by public sewers;
   4. (d) Counties and cities may prohibit or restrict the construction of accessory dwelling units on land designated as critical areas or their buffers as designated in RCW 36.70A.060, or in designated shoreline buffers, though conversions of internal space in legally permitted structures may be allowed;
   5. (e) Counties and cities may prohibit or restrict 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;
   6. (f) Counties and cities may prohibit or restrict the construction of accessory dwelling units in a watershed serving a reservoir for potable water if that watershed is or was listed, as of July 1, 2023, as impaired or threatened under section 303(d) of the federal Clean Water Act (33 U.S.C. Sec. 1313(d));
   7. (g) Counties and cities may prohibit or restrict the construction of accessory dwelling units in portions of cities within a one-mile radius of a commercial airport in Washington with at least 9,000,000 annual enplanements;
   8. (h) Counties and cities may prohibit or restrict the construction of accessory dwelling units in areas with other unsuitable physical characteristics of a property; and
   9. (i) Counties and cities may restrict the use of accessory dwelling units for short term rentals.
4. (4) The requirements of RCW 36.70A.681 shall supersede, preempt, and invalidate local development regulations in any county or city that has not passed ordinances, regulations, or other official controls within the time frames provided under RCW 36.70A.680.
5. (5) ADU regulations not subject to appeal. Any action taken by a county or city that is consistent with these requirements is not subject to legal challenge under chapter 36.70A or 43.21C RCW, unless the action has a probable significant adverse impact on fish habitat.

[Statutory Authority: RCW 36.70A.050 and 36.70A.190. WSR 25-17-058, s 365-196-880, filed 8/15/25, effective 9/15/25.]