Federal Way ADU rules
✓ Verified against code · August 20, 2026
Current rules under FWRC 19.200.180 (Accessory Dwelling Units), adopted by Ordinance 25-1016 §§30–31, in effect since June 3, 2025. Federal Way amended its ADU standards for HB 1337 in Ordinance 25-1016, effective June 3, 2025 — just ahead of the state's June 30 deadline. It is one of the few cities in this ledger still requiring an off-street parking space for an ADU outside the transit waiver, and the city has no water or sewer utility of its own, which turns utility connections into a real budget line.
Common questions, answered from the code
Do I need parking for a Federal Way ADU?
Usually yes — and that makes Federal Way stricter than most of its neighbours. One off-street space is required per ADU on top of the primary dwelling's parking, waived only if the ADU is within a half mile of a major transit stop. Cities like Seattle, Tacoma and Shoreline require none at all citywide, so if parking is the binding constraint on your lot, it is worth confirming your distance to transit early.
FWRC 19.200.180 · Permalink
How big can a Federal Way ADU be?
1,000 sq ft with a maximum of two bedrooms, and garage, workshop and similar non-living space does not count. There is a notable exception for attached units: an attached ADU may exceed 1,000 sq ft, up to the largest floor area of the primary dwelling, if creating it requires no more than minimal exterior alteration — which is the attic or basement conversion case.
FWRC 19.200.180 · Permalink
How tall can a Federal Way ADU be?
30 ft above average building elevation, and unusually, a detached ADU is allowed to be taller than the primary house. That is well above the 24 ft floor HB 1337 sets.
FWRC 19.200.180 · Permalink
What will utilities cost on a Federal Way ADU?
More than you might expect, because Federal Way has no water or sewer utility of its own. Service comes from Lakehaven, Tacoma Water, Midway Sewer or Highline Water depending on where you are, and a septic property needs King County Public Health sign-off before permitting. The city warns that ADU plumbing load can force a water meter or service-line upsizing, or a separate meter, and a detached unit needs its own sewer connection permit.
City Bulletin #048 · Permalink
What do impact fees cost on a Federal Way ADU?
Transportation impact fees for an ADU are capped at half the rate for a detached single-family dwelling. Other fees are not published in the ADU materials — the city directs applicants to contact the Permit Center, so budget for a conversation rather than a number.
FWRC 19.91.060(6) · Permalink
The rules at a glance
| ADUs allowed per lot | Two per property, with no restriction on the attached and detached mix.FWRC 19.200.180 |
| Maximum size | 1,000 sq ft and a maximum of two bedrooms, excluding garage, workshop and similar non-living areas. An attached ADU may exceed 1,000 sq ft — up to the largest floor area of the primary dwelling — where creating it needs no more than minimal exterior alteration, such as an attic or basement conversion.FWRC 19.200.180 |
| Detached ADU height | 30 ft above average building elevation, and a detached ADU may be taller than the primary house.FWRC 19.200.180 |
| Detached ADU setbacks | In the RS 35.0 zone, 20 ft front and 10 ft side and rear; in other RS zones, 20 ft front and 5 ft side and rear, with a 10 ft side setback on a corner lot's non-primary-access side. ADUs are barred from required yards except where the lot abuts a public alley, in which case a detached ADU may sit on the lot line.FWRC 19.200.180 |
| Off-street parking | One off-street space per ADU, in addition to the primary dwelling's parking — waived entirely for an ADU within a half mile of a major transit stop.FWRC 19.200.180 |
| Owner-occupancy | Not required. No owner-occupancy condition appears in the current code or the city's own ADU handout. We verified its absence from the current text rather than finding the provision that repealed it by name.FWRC 19.200.180 (absence verified) |
| Lot coverage / floor area | The ADU, accessory structures, driveway and primary dwelling together must stay within the zone's maximum lot coverage: 50% in RS 35.0 and RS 15.0, 60% in RS 9.6, RS 7.2 and RS 5.0, and 10% in SE.FWRC 19.200.010; 19.190.010; 19.200.180 |
| Permit path & timeline | A standard building permit through the Permit Center, electronic submittal only, with no separate land-use approval identified for a code-conforming ADU. No published review timeline or ADU fee schedule.FWRC 19.200.180; City Bulletin #048 |
Worth knowing
- Transportation impact fees for an ADU are capped at 50% of the fee for a detached single-family dwelling (FWRC 19.91.060(6)).
- A detached ADU may be factory-built or a manufactured home.
- Federal Way runs no water or sewer utility of its own — service comes from Lakehaven, Tacoma Water, Midway Sewer or Highline Water, and a septic ADU needs King County Public Health approval before permitting. The city itself flags that ADU plumbing load may force a water meter or service-line upsizing, or a separate meter, plus a separate sewer connection permit for a detached unit.
- South King Fire access standards apply: a 20-ft-wide access road at no more than 16% grade, a turnaround beyond 150 ft, a hydrant within 350 ft, and 1,750 gpm fire flow for units over 3,600 sq ft or sprinklers instead.
- An ADU must stand at least 10 ft from other structures, or use fire-rated construction.
On our watchlist
Title 19 is published as current through Ordinance 26-1048 (July 7, 2026). The ADU section's own amendment history ends at Ordinance 25-1016, indicating 26-1048 did not touch it, but we have not read that ordinance directly.
Short-term rental treatment of ADUs was not located in the sections reviewed — its absence is not confirmed.
No pre-approved plan program or published permit timeline was found.
Primary sources
- FWRC 19.200.180 (codified)
- City of Federal Way Bulletin #048 — Accessory Dwelling Units
- FWRC 19.91 (impact fees)
Other Washington cities
Auburn · Bellevue · Bellingham · Bothell · Burien · Edmonds · Everett · Issaquah · Kent · Kirkland · Lynnwood · Olympia · Puyallup · Redmond · Renton · Sammamish · Seattle · Shoreline · Spokane · Tacoma · Vancouver
Not legal advice. Every fact above cites the code section it comes from — check the cite, or ask your city’s planning department to confirm your specific lot. Spotted an error or a new ordinance? See about to reach us; corrections are logged in the changelog.