ADU Rulebook

City · Washington

ADU rules in Renton

5 sources

These are the primary sources for accessory dwelling unit regulations in Renton: the city's own zoning code, planning department pages, and permit guides. Start here before talking to anyone: the rules below are what your permit reviewer will apply.

Rules at a glance

Detached (backyard) ADU
Allowed

Two ADUs are allowed per legal lot as an accessory use to a principal dwelling, in any configuration: one attached plus one detached, two attached, or two detached. Detached ADUs must sit at least 4 ft from any residential structure (otherwise treated as attached) and are capped at 24 ft height; they may be sited at the rear lot line where an alley is present. In RC, R-1, R-4, R-6, and R-8 zones a second ADU must meet the principal dwelling's location and setback requirements.

RMC 4-2-110C.4 (General Requirements: Maximum Number of Units, Configuration; Detached ADUs)
Attached or internal ADU
Allowed

ADUs may be established within or as an addition to the principal dwelling. Attached and internal ADUs follow the setback and height standards of primary structures (RMC 4-2-110A and 4-2-110B).

RMC 4-2-110C.4 (Configuration; Attached and Internal ADUs)
Maximum size
1,000 sq ft gross floor area and 1,000 sq ft building area per ADU; a conversion occupying an entire single floor of the primary dwelling may go larger, up to 1,250 sq ft (beyond that it is classified as an attached dwelling, not an ADU); PRADU base-plan ADUs are exempt from the building area cap

Gross floor area is interior habitable area excluding attached garages, accessory structures, porches, and exterior stairs (RMC 4-2-110I note 40); building area includes garages and utility rooms (note 41). ADUs accessory to a religious institution or social service org: up to 3 units, 3,000 sq ft aggregate, 1,000 sq ft each (RMC 4-2-080.A.7.b).

RMC 4-2-110C.4 (Maximum Gross Floor Area, Maximum Building Area, Conversions); RMC 4-2-110I notes 25, 26, 40, 41
Owner occupancy
Not required

The current ADU development standards (as amended by Ord. 6160, 6-16-2025 for HB 1337 compliance) contain no owner occupancy requirement, and city staff on the official HB 1337 page state: 'In compliance with HB 1337 onsite owner occupancy is not required. Both units are permitted for use as rental units.' Exception: under RMC 4-4-055.B.2 a dwelling used as a short-term rental must be owner-occupied if multiple parties rent at the same time.

RMC 4-2-110C (no owner occupancy provision); RMC 4-4-055.B.2
Extra parking
Minimum 1.0 off-street space per ADU; no off-street parking required for ADUs on lots within a one-half mile walking distance of a major transit stop (Area A)

Transit proximity is measured by a city-mapped walkshed; lots partially within the walkshed are treated as entirely within (RMC 4-2-110I note 20). One additional space is required if the unit is used as an owner-occupied short-term rental (RMC 4-4-055.B.4).

RMC 4-2-110C.4 (Parking); RMC 4-2-110I note 20
Approval process
Permitted use

The zoning use table lists 'Accessory dwelling unit' as AC7 in the RC, R-1, R-4, R-6, R-8, R-10, and R-14 zones; AC means Accessory Use in the RMC 4-2-050 legend, so ADUs are allowed outright with a building permit, no conditional use permit. A Conditional Use Permit is required only for ADUs accessory to a nonresidential use by a religious institution or social service organization (RMC 4-2-080.A.7.a).

RMC 4-2-060.C; RMC 4-2-050.C.1; RMC 4-2-080.A.7
Rental restrictions
No minimum lease term and no ADU-specific rental restrictions; the city confirms both units on a lot may be used as rentals. Short-term rental (advertised for under 30 continuous days) of any dwelling unit requires a City of Renton business license, and the dwelling must be owner-occupied if multiple parties rent at the same time; guests limited to two per bedroom

STR violations are a misdemeanor under RMC 1-3-1.

RMC 4-4-055 (no ADU rental provisions in RMC 4-2-110C)
The fine print: 8 caveats that can change the picture
  • ADU standards apply only in the RC, R-1, R-4, R-6, R-8, R-10, and R-14 residential zones, on lots with a principal dwelling (RMC 4-2-110C.2).
  • Two ADUs per lot, but in RC, R-1, R-4, R-6, and R-8 zones the second ADU must comply with the location and setback requirements applicable to the principal dwelling (RMC 4-2-110C.4).
  • Lots accessed via a shared driveway are limited by the shared driveway unit cap in RMC 4-6-060J (RMC 4-2-110I note 24).
  • PRADU (Permit Ready ADU) base-plan ADUs are exempt from the maximum building area and maximum building height limits if built in conformance with the approved base plan (RMC 4-2-110I notes 26 and 42).
  • Conversions of accessory buildings and dwellings constructed before June 30, 2025 are exempt from development regulations including lot coverage, setbacks, and size; post-June-30-2025 modifications that increase nonconformance lose the exemption (RMC 4-2-110I note 25).
  • Detached ADU side setbacks vary by zone: 25 ft in RC and R-1, 5 ft in R-4/R-6/R-8, 4 ft in R-10/R-14; rear setback 5 ft with a 25% rear-yard open-length rule within 10 ft of the rear line.
  • RMC 4-2-116 (former ADU residential design standards) is now Reserved (repealed by Ord. 6160); design standards live in RMC 4-2-115. Search engines still surface the dead 4-2-116 URL.
  • Renton's code is on Code Publishing at codepublishing.com/WA/Renton; renton.municipal.codes does NOT exist (General Code returns Site Not Found).

Summarized from Renton's ordinance text, read July 2026; every row links the code section it came from. Rules often vary by zone and lot, so treat this as orientation, not a permit determination, and confirm with the planning department before you commit to a design.

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ADU regulations

Short-term rental rules

Planning to rent your ADU on Airbnb or VRBO? Renton regulates short-term rentals separately; check these before counting on nightly rental income.

Washington statewide law also applies

Washington sets baseline ADU rights at the state level. Where local rules are stricter than state law allows, state law usually wins, so both are worth reading.

See Washington statewide rules

Spotted something outdated?

Zoning codes change. If a link is dead or Renton has updated its ordinance, report it and we'll verify against the official source.

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