wa-law.org > bill > 2025-26 > SB 5413 > Original Bill

SB 5413 - Detached ADUs

Source

Section 1

  1. Counties may allow detached accessory dwelling units outside of urban growth areas if the county meets the requirements in subsections (2) and (3) of this section, and such detached accessory dwelling units are subject to development regulations that include the following limitations:

    1. No parcel may have more than one attached or detached accessory dwelling unit;

    2. The detached accessory dwelling unit is subject to the water supply requirements of RCW 19.27.097 and any groundwater mitigation requirements adopted by the county or the department of ecology;

    3. The applicant must provide documentation that the existing or proposed sewage or septic system is capable of handling the additional demand placed upon it by the detached accessory dwelling unit;

    4. The gross floor area of the detached accessory dwelling unit does not exceed the gross floor area of what could be authorized by the county as an expansion of the primary dwelling to create an attached accessory dwelling unit and is, in no case, greater than 1,296 square feet. Floor areas are exclusive of garages, porches, and unfinished basements;

    5. The detached accessory dwelling unit must utilize the same driveway as the principal unit;

    6. The detached accessory dwelling unit must be sited within 150 feet of the principal unit;

    7. The detached accessory dwelling unit may be the existing principal unit if the existing principal unit meets the requirements of this subsection, is a single-family dwelling unit, and a new principal unit that is a single-family dwelling unit is constructed on the same parcel;

    8. A parcel may not be subdivided for the purposes of avoiding the limits on development regulations described in this subsection;

      1. If the detached accessory dwelling unit is offered as a short-term rental as defined in RCW 36.70A.696, the primary unit must be owner-occupied;

    9. The combined water withdrawal for the detached accessory dwelling unit, the primary unit, and any other domestic uses on the parcel must not exceed the use limitations in RCW 90.44.050 for domestic use;

    10. The detached accessory dwelling unit must be subject to the water supply requirements in RCW 19.27.097; and

    11. Withdrawals of water by each dwelling unit on the parcel must be metered.

  2. Counties may only allow detached accessory dwelling units outside of urban growth areas if they have the following code enforcement measures in place:

    1. A voluntary county code compliance process through which the owner of an unpermitted detached accessory dwelling unit can bring the unpermitted detached accessory dwelling unit into compliance with applicable regulations. In such a case, a permit penalty of at least double the normal permit fee applies.

    2. Owners who do not seek voluntary compliance and are found to have constructed or placed a detached accessory dwelling unit without all required permits are subject to a civil infraction of at least $1,000 and are required to remove the detached accessory dwelling unit or ensure that it meets all existing development regulations, if applicable. A penalty of at least triple the normal permit fee is also required if the accessory dwelling unit remains and meets all existing development regulations.

    3. Any owner who does not seek voluntary compliance and who received a civil infraction for constructing or placing an accessory dwelling unit without all required permits is prohibited from receiving any permits for the placement or construction of new accessory dwelling units for a period of at least three years.

  3. Counties may allow detached accessory dwelling units outside of urban growth areas if the county takes the following actions to account for detached accessory dwelling unit development:

    1. Tracks and reports to the department annually the number of detached accessory dwelling unit permits completed;

    2. Updates the county's comprehensive land use plan during the county's next required review and all subsequent reviews according to RCW 36.70A.130(5)(b) to properly account for the number of detached accessory dwelling units completed since the effective date of this section and the projected development over the next 20-year planning period utilizing the data collected and reported in (a) of this subsection within the overall underlying density outside of urban growth areas;

    3. Makes future amendments to the county's comprehensive land use plan accounting for actual and projected detached accessory dwelling units within the overall underlying density outside of urban growth areas no more than once every five years.

  4. Subsection (1) of this section is in addition to other county authority enumerated in this chapter and does not:

    1. Affect or modify the validity of any county ordinance authorizing accessory dwelling units adopted prior to the effective date of this section;

    2. Exclude other means of authorizing accessory dwelling units in urban or rural areas, if consistent with this act; or

    3. Exclude other innovative techniques under RCW 36.70A.070(5)(b), 36.70A.090, or 36.70A.177, if consistent with this section.

Section 2

The definitions in this section apply throughout RCW 36.70A.697, 36.70A.698, 36.70A.680, 36.70A.681, and section 1 of this act unless the context clearly requires otherwise.

  1. "Accessory dwelling unit" means a dwelling unit located on the same lot as a single-family housing unit, duplex, triplex, townhome, or other housing unit.

  2. "Attached accessory dwelling unit" means an accessory dwelling unit located within or attached to a single-family housing unit, duplex, triplex, townhome, or other housing unit.

  3. "City" means any city, code city, and town located in a county planning under RCW 36.70A.040.

  4. "County" means any county planning under RCW 36.70A.040.

  5. "Detached accessory dwelling unit" means an accessory dwelling unit that consists partly or entirely of a building that is separate and detached from a single-family housing unit, duplex, triplex, townhome, or other housing unit and is on the same property.

  6. "Dwelling unit" means a residential living unit that provides complete independent living facilities for one or more persons and that includes permanent provisions for living, sleeping, eating, cooking, and sanitation.

  7. "Gross floor area" means the interior habitable area of a dwelling unit including basements and attics but not including a garage or accessory structure.

  8. "Major transit stop" means:

    1. A stop on a high capacity transportation system funded or expanded under the provisions of chapter 81.104 RCW;

    2. Commuter rail stops;

    3. Stops on rail or fixed guideway systems, including transitways;

    4. Stops on bus rapid transit routes or routes that run on high occupancy vehicle lanes; or

    5. Stops for a bus or other transit mode providing actual fixed route service at intervals of at least fifteen minutes for at least five hours during the peak hours of operation on weekdays.

  9. "Owner" means any person who has at least 50 percent ownership in a property on which an accessory dwelling unit is located.

  10. "Principal unit" means the single-family housing unit, duplex, triplex, townhome, or other housing unit located on the same lot as an accessory dwelling unit.

  11. "Short-term rental" means a lodging use, that is not a hotel or motel or bed and breakfast, in which a dwelling unit, or portion thereof, is offered or provided to a guest by a short-term rental operator for a fee for fewer than 30 consecutive nights.

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