Can I build a backyard home in Federal Way?
Since 2023, Washington law lets most city lots hold up to two more homes. Federal Way writes its own rules on top. Here’s what the code says, in plain English — and a free report on what may fit on your lot.
What Federal Way allows.
The headline standards. Tap any one for the full wording and the code section.
ADUs per lot2 per subject propertyFull wording
2 per subject property (FWRC 19.200.180 note 2). With a detached house and middle housing, up to 6 total units per lot (FWRC 19.200.010 note 2).
Max size1,000 sq ft (garage and workshop not counted); 2 bedrooms maxFull wording
1,000 sq ft per ADU, excluding garage, workshop and similar nonliving areas; no more than 2 bedrooms. An attached ADU created without exterior alteration may reach the primary unit's largest floor area (FWRC 19.200.180 note 9).
Max height30 ft above average building elevationFull wording
30 ft above average building elevation (FWRC 19.200.180); ADUs may be taller than the primary building (FWRC 19.265.010(3)).
Front setback20 ft in all RS zonesFull wording
20 ft in all RS zones (FWRC 19.200.180).
Side setback5 ftFull wording
5 ft (10 ft in RS 35.0; 10 ft on a corner lot's street side away from the primary vehicle access) (FWRC 19.200.180 note 3).
Rear setback5 ftFull wording
5 ft (10 ft in RS 35.0); a detached ADU may be sited at a lot line abutting a public alley (FWRC 19.200.180 note 4).
Lot coverage60% in RS 7.2, RS 9.6 and RS 5.0Full wording
60% in RS 7.2, RS 9.6 and RS 5.0 (50% in RS 15.0 and RS 35.0), shared by the primary unit, ADUs and accessory structures (FWRC 19.200.010 note 6; 19.200.180 note 2).
Parking1 space per ADUFull wording
1 space per ADU; 0 spaces within 1/2 mile of a major transit stop (FWRC 19.200.180).
Where a city figure reads stricter than the state floor (RCW 36.70A.681), the floor may control — the report flags it for your parcel.
Living there, selling it, plans, time and fees.
Each answer is the code’s own wording, with the section it comes from. “Not published yet” means the city hasn’t posted a figure — the report asks the city, not the internet.
Are backyard homes allowed?
Yes — freestanding detached and attached ADUs are permitted in the single-family residential (RS) zones (FWRC 19.200.180; ADU definition FWRC 19.05.040).
Minimum lot size
None separate for an ADU; it follows the minimum lot size for the existing primary dwelling, and ADUs may be permitted on legally nonconforming lots (FWRC 19.200.180 note 1; 19.105.010(3))
Do you have to live there?
No — FWRC 19.200.180 (Ord. 25-1010) has no owner-occupancy requirement.
Can it be sold on its own?
Not addressed; RCW 36.70A.681 floor applies
Pre-approved plans
None found
How long the city takes
Not published
Impact fees
Not found; RCW 36.70A.681 caps ADU impact fees at 50% of the principal unit's
Plans Federal Way has already approved.
A pre-approved plan skips the design review: Federal Way has already checked the drawings, so the permit review is about your lot.
Loading the plans…
Pictures are the official pages’ own. A pre-approved plan is not a permit: the city still reviews your site.
The code is half the answer. Your parcel is the other half.
Lines and easements
Where the lot lines really are, which setbacks apply on each side, and whether a utility or access easement takes the corner you had in mind.
Critical areas and slope
Steep slopes, wetlands and streams come with buffers that no citywide number shows. The report reads the county’s maps for your parcel.
Sewer, septic, water, trees
Whether sewer reaches the lot or it’s on septic, where the water service is, and which trees a city protects — the things that decide where a unit can actually go.
What Federal Way allows, what could fit on your lot, and a planning cost range. If something won’t fit, the report says so — and shows what might.
Where this page comes from.
Read from the Federal Way municipal code and the city’s own pages on November 5, 2026. The same table feeds the HousUp report, so the report and this page never disagree. Cities amend their codes; before you design anything, confirm the current wording with the city.
2 sources, read November 5, 2026
Find out what your property could become.
Type your address. Within a few hours: what Federal Way allows, what could fit, and a planning cost range. Free, no obligation.