SB 5413
In CommitteeSenate
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?
- Introduced: The bill is filed and assigned a number.
- Committee: A subject-matter committee holds hearings, takes public testimony, and decides whether to advance the bill.
- Floor Vote: The full chamber (House or Senate) debates and votes on the bill.
- Opposite Chamber: The bill repeats the committee and floor vote process in the other chamber.
- Governor: The Governor reviews the bill and decides whether to sign or veto it.
- Signed: The bill has been signed into law.
AI Analysis
This bill allows counties to permit detached accessory dwelling units (ADUs) outside urban growth areas, but only under strict rules limiting size, location, water use, and enforcement. It adds new requirements for counties to track and plan for such units while strengthening penalties for noncompliance.
- Counties may allow detached accessory dwelling units (ADUs) outside urban growth areas, but only if they meet strict development and enforcement requirements.
- Each parcel can have at most one attached or detached ADU, and the detached ADU cannot exceed 1,296 square feet or be sited more than 150 feet from the main house.
- Detached ADUs must use the same driveway as the main house, comply with water use limits (metered and within state domestic use caps), and prove sewage systems can handle added demand.
- Counties must enforce strong penalties: at least $1,000 civil infractions and permit denials for up to three years for unpermitted ADUs that aren’t voluntarily brought into compliance.
- Counties must track ADU permits, update land use plans every 5 years to include ADU data, and report annually to the Department of Ecology.
Who is affected
- Rural homeowners — Homeowners in unincorporated county areas (outside urban growth areas) who want to build or already have a detached ADU on their property; they must follow new rules if counties allow such units.
- County governments — Local governments in counties outside urban growth areas must adopt and enforce new rules for detached ADUs, including tracking permits, updating land use plans, and enforcing penalties.
- Short-term rental operators — People seeking to rent out a detached ADU as a short-term rental must ensure the main house is their primary residence and comply with water use and permit rules.
- Water resource agencies — Water resource managers and the Department of Ecology must ensure new detached ADUs comply with state water use limits and mitigation requirements.
Pro/Con Analysis
Potential Benefits (4)
Allows rural homeowners to build one small (≤1,296 sq ft) detached ADU on their property—potentially increasing local housing supply, supporting multigenerational living, or generating modest rental income—without requiring new infrastructure or urban expansion.
HousingPeopleRef: Sec. 1(1)(a), (d)Restricting short-term rentals to owner-occupied primary units and capping water use helps prevent illegal short-term rental proliferation and protects rural water resources, balancing housing needs with community-scale environmental sustainability.
Public SafetyPeopleRef: Sec. 1(1)(i), (j)Mandates strong enforcement tools (e.g., civil infractions, permit denial periods) that deter illegal ADUs and promote fairness, reducing the risk of unregulated development undermining planning goals and public trust in land use administration.
Local GovernmentPeopleRef: Sec. 1(2)(a)-(c)Requires counties to collect and report ADU data and integrate it into long-term land use planning—improving transparency and evidence-based planning, which can support more equitable rural development decisions over time.
Local GovernmentLean peopleRef: Sec. 1(3)(a)-(c)
Potential Concerns (5)
Counties must implement costly enforcement mechanisms—including civil infractions of at least $1,000, permit denials for up to three years, and voluntary compliance processes—for detached ADUs, which may strain limited county planning and code enforcement resources, especially in rural counties with small staffs.
Local GovernmentPeopleRef: Sec. 1(1)(c), (2)(b)Counties are required to track permits, update comprehensive plans every 5 years with ADU data, and report annually to the Department of Ecology—adding administrative burden without new state funding, potentially diverting staff time from other priorities.
Local GovernmentRef: Sec. 1(3)(a)-(c)While the bill strengthens water use limits and requires metering and sewage capacity verification, rural homeowners may struggle to meet these technical requirements (e.g., septic upgrades, meter installation), potentially limiting ADU feasibility for lower-income households and discouraging small-scale housing solutions in water-stressed areas.
EnvironmentPeopleRef: Sec. 1(1)(b), (j), (k)The 150-foot siting and shared driveway requirements may be incompatible with irregular rural topography or small parcels, reducing practical feasibility for some homeowners—especially those with topographically constrained lots—without clear benefit to public goods.
HousingRef: Sec. 1(1)(e), (f)The prohibition on parcel subdivision to avoid ADU limits may prevent legitimate lot splits for inheritance or farm succession, potentially interfering with intergenerational land use planning in rural communities.
HousingRef: Sec. 1(1)(h)
Who Is Most Affected
Rural homeowners gain the option to build small ADUs, but must meet strict technical and regulatory requirements. Lower-income homeowners may struggle with septic upgrades, metering, and permit costs, while wealthier or more technically equipped homeowners benefit most from the flexibility.
Counties gain authority to allow ADUs but must invest in new enforcement, tracking, and planning capacity—without state funding. Smaller, rural counties face disproportionate administrative burden and may scale back other services to comply.
Short-term rental operators are effectively excluded from profiting via detached ADUs unless they live on-site, limiting speculative investment but preserving owner-occupancy intent. This protects neighborhood character but reduces potential income for some.
Water resource agencies gain stronger regulatory leverage over domestic water use and can better track demand, supporting compliance with state water laws. However, they must monitor county-level enforcement, adding oversight burden.