ADU rules in Federal Way

Detached ADUs are outright permitted in both zones where Federal Way allows houses: the Single-Family Residential zones (RS 35.0, RS 15.0, RS 9.6, RS 7.2, RS 5.0) and the Suburban Estate (SE) zone. The use zone charts at FWRC 19.200.180 and 19.195.180 list 'Accessory dwelling unit (ADU)' with a Required Review Process of 'None', and note 2 allows up to two ADUs per subject property in any mix of attached and detached. Note 4 allows ADUs in existing structures, including ones that are legally nonconforming for setbacks or lot coverage, and allows a detached ADU to sit right at a lot line that abuts a public alley. Setbacks match those for the main house (20 ft front; 10 ft side and rear in RS 35.0, otherwise 5 ft side and rear with 10 ft on the street side of a corner lot), and height is capped at 30 ft above average building elevation. Ordinance No. 25-1010, adopted May 6, 2025, rewrote both charts to implement EHB 1337; ADUs remain unlisted, and therefore not permitted, in the Multifamily Residential (RM) zone and the commercial zones.

Attached and internal ADUs are permitted on exactly the same terms as detached ones; Federal Way regulates a single ADU use rather than splitting the charts by type. FWRC 19.05.040 defines an ADU as a unit that is either a freestanding detached structure or one sharing vertical and/or horizontal walls with the primary dwelling, so long as there is no interior connection or the connection is securable by lock from within the ADU, which covers basement units, attic conversions, and additions. Note 8 of FWRC 19.200.180 says attached ADUs may be accessed through the entrance to the primary dwelling unit (the SE chart adds 'or through an additional entrance'), so no separate exterior door is forced on a conversion. Note 4 allows conversion of existing structures, including detached garages that violate current setback or lot coverage standards. The two-ADU allowance can be filled with two attached units, two detached units, or one of each.

Note 9 of FWRC 19.200.180 (notes 7 and 8 in the SE chart) sets the cap at 1,000 sq ft per ADU, measured excluding any garage, workshop and similar nonliving areas, with a maximum of two bedrooms. The attached exception is aimed at attic and basement conversions: an attached ADU may run up to the largest floor area of the primary dwelling unit if creating it does not necessitate an exterior alteration of the residence, apart from alterations needed to make the ADU a functional separate residence. FWRC 19.265.010(3) carves ADUs out of the general accessory-structure rule, so an ADU may be taller than the main house and equal to it in gross square footage. The binding constraint on a large lot build is usually lot coverage: the ADUs, other accessory structures and the house together must stay under the zone maximum, which is 50 percent in RS 35.0 and RS 15.0, 60 percent in RS 9.6, RS 7.2 and RS 5.0, and 10 percent in SE.

Federal Way imposes no owner occupancy condition on ADUs. Neither ADU use zone chart (FWRC 19.200.180 and 19.195.180) nor the definition at FWRC 19.05.040 says anything about who must live on the lot, and a full-text search of the Federal Way Revised Code as codified through Ordinance 26-1045 returns 'owner occupancy' only in FWRC 18.55 (subdivision design criteria), FWRC 3.30 (multifamily property tax exemption) and the archived text of Ordinance 22-932. The requirement belonged to the pre-2022 rules and was dropped over the city's three-step modernization: Ord. No. 22-932 (May 3, 2022), Ord. No. 23-963 (July 5, 2023) and Ord. No. 25-1010 (May 6, 2025). This also matches RCW 36.70A.681(1)(b), which since Federal Way's periodic comprehensive plan update deadline has barred the city from requiring the owner to reside in the ADU or another unit on the same lot. The city's June 2025 handout (Bulletin #048) likewise lists no occupancy condition.

The Required Parking Spaces column of both ADU use zone charts reads '1 parking space per unit / 0 within 1/2 mile of major transit stop'. That space is in addition to the two spaces per dwelling unit the primary house owes under FWRC 19.200.010. 'Major transit stop' is defined at FWRC 19.05.130 by direct reference to RCW 36.70A.696 for ADU purposes, which pulls in light rail and bus rapid transit stops, so much of the city near the Sound Transit Federal Way Link Extension stations falls in the zero-parking band; confirm your address with the Planner on Duty rather than eyeballing the distance, since the state measure is walking distance. The city's June 2025 handout says the same thing in plain English. FWRC 19.130.240(1)(b) lets a front-yard driveway or parking pad exceed 20 ft in width when it serves an ADU on a lot at least 60 ft wide, or when the width at the right-of-way stays at 20 ft or less.

Ministerial. Both ADU use zone charts list the Required Review Process as 'None', which means no Process I through IV land use review under FWRC Chapters 19.55 to 19.70, no discretionary decision and no public hearing. An ADU is built on a building permit: the city's Bulletin #048 handout tells applicants to use it alongside a building permit checklist and submit electronically. The remaining sign-offs are non-discretionary: certificates of water and sewer availability before application (the city has no utilities of its own, so Lakehaven, Tacoma Water, Highline Water or Midway Sewer issue them), King County Public Health approval for a septic-served ADU, South King Fire and Rescue access, hydrant and fire-flow standards, and a 10 ft separation from other structures or rated construction instead. ADUs are expressly exempt from transportation concurrency review under FWRC 19.90.060(2)(r) and from school impact fees under FWRC 19.95.060(1)(d); transportation and park impact fees are capped at 50 percent of the detached single-family rate.

Nothing in FWRC 19.200.180, 19.195.180 or 19.05.040 conditions an ADU on who occupies it or limits renting it, and the code has no residential rental license or inspection chapter (searches for 'rental housing' and 'landlord' return only the voter-approved Good Cause Eviction Ordinance at FWRC Chapter 20.05, which does apply to ADU tenancies). A full-text search of the code returns zero hits for 'short-term rental', 'vacation rental' and 'bed and breakfast', so Federal Way simply has not legislated on nightly rental. Treat whole-unit short-term rental as unsettled rather than blessed: FWRC 19.190.060(1) permits only uses listed for the district, 'hotel, motel' is listed only in the City Center Core and City Center Frame zones (FWRC 19.225.050 and 19.230.050) and carries its own license under FWRC Chapter 12.55, and RCW 36.70A.680(5)(a) expressly preserves the city's power to restrict ADU short-term rentals later. Separate sale is available: FWRC 18.70.010(1)(d), added by Ord. No. 25-1017 on June 3, 2025, allows non-stacked ADUs to be unit lot subdivided (processed as a short plat for nine or fewer unit lots), and state law bars prohibiting condominium conveyance of a unit built as an ADU.