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Evergreen Ledger

2SSB 5470

In Committee

Senate

Detached ADUs

Establishing limitations on detached accessory dwelling units outside urban growth areas.

This status may be delayed. See Action History below for the latest updates.

How does a bill become law?
  1. Introduced: The bill is filed and assigned a number.
  2. Committee: A subject-matter committee holds hearings, takes public testimony, and decides whether to advance the bill.
  3. Floor Vote: The full chamber (House or Senate) debates and votes on the bill.
  4. Opposite Chamber: The bill repeats the committee and floor vote process in the other chamber.
  5. Governor: The Governor reviews the bill and decides whether to sign or veto it.
  6. Signed: The bill has been signed into law.
Introduced: February 3, 2026
Last Action: February 26, 2026
Status: S Rules X
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AI Analysis

This analysis was generated by AI and may contain errors. It is not legal advice. Always refer to the official bill text for authoritative information.
People & CommunitiesPeople-leaningCorporate & Wealthy Interests

This bill allows counties outside urban growth areas to permit detached accessory dwelling units (ADUs), but only under strict rules limiting size, location, water use, and sewage capacity. It also requires counties to track and report ADU permits and update long-term land-use plans to account for this new development type.

  • Counties outside urban growth areas may allow detached accessory dwelling units (ADUs), but only if they adopt specific rules limiting size, location, water use, and sewage capacity.
  • Each parcel is limited to one attached or detached ADU, and the detached ADU may not exceed 1,296 square feet (or the size allowed for an attached ADU expansion, whichever is smaller).
  • Detached ADUs must be within 150 feet of the main house, use the same driveway, and cannot be on a separately subdivided lot.
  • Water and sewage systems must meet strict requirements: water use must stay within state limits for domestic use, and sewage capacity must be verified before approval.
  • Counties must annually report ADU permits to the Department of Ecology and update their comprehensive land-use plans every five years to reflect ADU growth.
  • If a detached ADU is used as a short-term rental, the main house must be owner-occupied.

Who is affected

  • County governments — Counties outside urban growth areas gain the option (but not requirement) to allow detached ADUs, but must adopt specific rules and reporting requirements to do so.
  • Property owners in rural/unincorporated areas — Homeowners in rural or unincorporated areas may be able to build or convert structures into detached ADUs, but must meet strict size, location, water, and sewage limits.
  • Local planning and building departments — Local planning and building departments must track ADU permits, update long-term land-use plans, and enforce new development rules.
  • Short-term rental operators — Short-term rental operators (e.g., Airbnb hosts) using a detached ADU must live in the main house on the property.
Effective: March 30, 2025Fiscal impact: May require counties to hire or reassign staff to track permits and update comprehensive plans; no direct state fiscal impact mentioned.
Model: Intel/Qwen3-Coder-Next-int4-AutoRoundGenerated: Mar 19, 2026 at 8:59 PM

Pro/Con Analysis

Potential Benefits (5)

  • Provides rural homeowners with a new, legally viable path to add housing units—potentially increasing local housing supply, supporting multigenerational living, and enabling modest rental income—especially valuable in areas with limited zoning flexibility.

    HousingPeopleRef: Sec. 1(1); Sec. 1(2)(a)

  • Mandating sewage capacity verification and water use compliance helps prevent overburdening rural water resources and septic systems, protecting groundwater and surface water quality in sensitive rural watersheds.

    EnvironmentPeopleRef: Sec. 1(1)(c), (b), (j); RCW 19.27.097

  • Requires counties to proactively plan for ADU growth in comprehensive plans, improving long-term infrastructure coordination and potentially reducing future conflicts over water, roads, and schools in rural areas.

    Local GovernmentPeopleRef: Sec. 1(2)(b), (c)

  • The owner-occupancy rule for short-term rentals may reduce transient tourism pressure in rural areas and encourage more stable, neighborhood-compatible uses of ADUs—though it limits investment flexibility.

    HousingLean peopleRef: Sec. 1(1)(i)

  • Shared driveway and proximity rules may reduce visual and traffic impacts in rural neighborhoods, addressing community concerns about incompatible development while preserving rural character.

    HousingLean peopleRef: Sec. 1(1)(e), (f)
Potential Concerns (5)

  • Strict water and sewage requirements may prevent many rural homeowners from building ADUs, especially those with older septic systems or wells, limiting housing flexibility without addressing underlying infrastructure constraints.

    EnvironmentPeopleRef: Sec. 1(1)(b), (j); RCW 19.27.097; RCW 90.44.050

  • The 1,296 sq ft cap, 150-foot proximity rule, and shared driveway requirement significantly limit the utility of detached ADUs for multigenerational living, rental income, or independent living—reducing their practical impact for most rural homeowners.

    HousingPeopleRef: Sec. 1(1)(d), (f), (e)

  • The owner-occupancy requirement for short-term rentals excludes low- and middle-income property owners who rely on short-term rentals as a primary income source, favoring wealthier owners who can afford to live on-site while renting out the ADU.

    HousingPeopleRef: Sec. 1(1)(i); RCW 36.70A.696(11)

  • Mandating comprehensive plan updates every five years (plus annual permit tracking) imposes new administrative burdens on rural counties with limited planning staff, potentially diverting resources from other critical infrastructure or housing needs.

    Local GovernmentLean peopleRef: Sec. 1(2)(c); RCW 36.70A.130(5)(b)

  • The prohibition on parcel subdivision to avoid ADU limits may inadvertently penalize families seeking to create separate housing for adult children or aging parents on multi-generational parcels, reducing flexibility for informal kinship arrangements.

    HousingLean peopleRef: Sec. 1(1)(h)

Who Is Most Affected

Rural homeowners (modest means)Mixed Impact

Rural homeowners with modest means may benefit if they can meet water/septic requirements and use the ADU for family housing or long-term rentals; but those with outdated infrastructure or lower equity may be excluded.

Rural renters and potential ADU tenantsPositive Impact

May gain new housing options and potential rental income, but face higher upfront costs to meet water/septic compliance and may be excluded if they lack equity to build or retrofit.

County planning and building departmentsMixed Impact

Will face new administrative duties (permit tracking, plan updates), but may benefit from improved long-term planning data and reduced unplanned development pressure.

Short-term rental operators (investor class)Negative Impact

Short-term rental operators (especially non-owner-occupying investors) are effectively excluded from using detached ADUs under this bill, reducing their flexibility and potential returns.

Rural communities and local infrastructure providersMixed Impact

May benefit from increased local housing supply and reduced pressure to expand infrastructure, but could face strain if ADU growth outpaces water/septic capacity despite regulations.