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Washington HB 1337 — Accessory Dwelling Units Statewide (WA)

Tracked preemption from the Washington overlay bundle.

Overview

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Effective
2023-07-23
Sunset
—
Authority
state
Scope
state:WA
Other Washington preemptions
Washington HB 1110 — Middle Housing (Tier 1: cities >=75,000)Washington HB 1110 — Middle Housing (Tier 2: cities 25,000-75,000)Washington HB 1110 — Middle Housing (Tier 3: small cities in Tier 1 UGA)Washington SB 5184 — Lot Splitting for Housing CapacityWashington SB 5290 — Local Permit Review TimelinesWashington E2SHB 1220 — Comprehensive Plan Housing ObligationsWashington Growth Management Act — Zoning for Growth Targets
Primary-source summary
HB 1337 — Accessory Dwelling Units (2023)

Trigger predicate

When this evaluates true for a parcel, the law's preempted fields take precedence over base zoning.

parcel.base_zone_category ∈ {res_sf, res_mf, res_th, mu}

Preempted fields

7 fields on the base district schema are rewritten when the trigger fires.

FieldOpValueNote
base_districts[category=res_sf].allowed_usesaddaduADUs by-right in all residential zones
base_districts[category=res_sf].max_adus_per_lotfloor_at2At least 2 ADUs per lot allowed (attached, detached, or conversion)
base_districts[category=res_sf].adu_owner_occupancy_requiredoverrideFalseCities cannot require owner-occupancy for ADUs
base_districts[category=res_sf].adu_max_size_sffloor_at1000Cities cannot cap detached ADU size below 1,000 sf
base_districts[category=res_sf].adu_parking_ratiowaive—No off-street parking may be required within 1/2 mile of transit
base_districts[category=res_sf].adu_min_lot_size_sfcap_atbase SF minimum lot size
review_typewaive_discretionary—

Citation

Authority source
WA HB 1337 (2023) / RCW 36.70A.680-681
§ RCW 36.70A.680, 36.70A.681
https://app.leg.wa.gov/billsummary?BillNumber=1337&Year=2023

Research notes

Applies to all cities planning under GMA. Connection/impact fees limited for ADUs. Federal AICUZ/Part 77 conflict possible near JBLM, NAS Whidbey, Fairchild AFB where ADU height or density may conflict with accident potential zones or noise contours.