Can I build a backyard home in Tukwila?
Since 2023, Washington law lets most city lots hold up to two more homes. Tukwila 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 Tukwila allows.
The headline standards. Tap any one for the full wording and the code section.
ADUs per lot2 — one principal unit plus up to 2 ADUs, attached or detachedFull wording
2 — one principal unit plus up to 2 ADUs, attached or detached (TMC 18.50.220(B)(1)). ADUs count toward maximum density (TMC 18.10.040).
Max size1,400 sq ft maximumFull wording
1,400 sq ft maximum; a detached garage under the ADU does not count toward the limit (TMC 18.50.220(B)(2)).
Max height28 ft for detached ADUsFull wording
28 ft for detached ADUs (TMC 18.50.220(B)(3)).
Front setback15 ft in CR (same as the house)Full wording
Same as principal: 15 ft in CR; 7 ft to a qualifying front porch; 10 ft second front (TMC 18.10.040; 18.50.220(B)(4)).
Side setback5 ft in CR (same as the house)Full wording
Same as principal: 5 ft in CR (TMC 18.10.040).
Rear setback5 ft in CRFull wording
5 ft in CR; 0 ft for an alley DADU, because new ADUs are not subject to rear setbacks where the rear yard abuts an alley (TMC 18.10.040; 18.50.220(B)(4)).
Lot coverage50% maximum building footprintFull wording
50% maximum building footprint; 75% maximum development area coverage in CR (TMC 18.10.040).
Parking0 spacesFull wording
0 spaces — 'Accessory dwelling units: No parking required' (TMC Figure 18-7, as amended by Ord. 2765).
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 — ADUs may be attached to or detached from the principal unit (TMC 18.50.220(B)(1)). In the Community Residential (CR) zone, up to 2 units per lot may be accessory residences (TMC 18.10.040).
Minimum lot size
None for an ADU; zone minimum applies to new lots (TMC 18.10.040)
Do you have to live there?
No — TMC 18.50.220, as amended by Ord. 2765, 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 Tukwila has already approved.
A pre-approved plan skips the design review: Tukwila 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 Tukwila 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 Tukwila 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.
Find out what your property could become.
Type your address. Within a few hours: what Tukwila allows, what could fit, and a planning cost range. Free, no obligation.