Declares it is the policy of this state to promote and encourage the creation of accessory dwelling units in a manner that is effective in meeting the needs of its citizens for affordable housing while protecting and enhancing residential neighborhoods.

Provides that all cities, towns, and counties planning under RCW 36.70A.040 shall adopt or amend by ordinance and incorporate into their development regulations, zoning regulation, or other official control an authorization for the creation of accessory dwelling units that is consistent with this section. Any other city, town, or county may adopt an ordinance authorizing accessory dwelling units consistent with this act.

Provides that all accessory dwelling unit ordinances adopted or amended as required by this act: (1) Shall allow accessory dwelling units as provided for in the ordinance in all single-family residential zoning districts;

(2) Shall provide for accessory dwelling units that are contained within, attached to, or detached from the principal residence on the property; that is, shall provide for both accessory apartments and accessory cottages;

(3) Shall not include restrictions on the type of occupant living in an accessory dwelling unit nor require a relationship to the occupant of the principal residence on the property, but may include a restriction on the maximum number of occupants of an accessory dwelling unit;

(4) May set a reasonable range of floor area to be allowed for accessory dwelling units, in square feet or ratio to the principal residence on the property, or both, provided that written findings be included indicating that the range of floor area reasonably approximates the size range of one-bedroom apartments within or nearby the city, town, or county;

(5) May include a requirement for the provision of off-street parking for the accessory dwelling unit, up to a maximum of one space, and may include a procedure for waiver of this requirement;

(6) Shall provide that applications for the creation of accessory dwelling units are processed, including review and decision, solely through administrative procedures subject to clearly defined standards;

(7) Shall require that the applicable department within the jurisdiction prepare and publish clear procedures and standards not inconsistent with this section that shall apply to the review of and decisions on applications for accessory dwelling units;

(8) May include provisions for the registration of accessory dwelling units within the jurisdiction that were created before any authorizing ordinance or were otherwise not permitted as accessory dwelling units by the applicable jurisdiction;

(9) Shall require that a registration or other form of statement concerning each permitted accessory dwelling unit be filed with the applicable county department of records and elections for the real estate records on the subject property; and

(10) Shall require that the building, planning, or other official of the city, town, or county report annually to the legislative body regarding the permitting and registration of accessory dwelling units.