Can I build a backyard home in Steilacoom?
Since 2023, Washington law lets most city lots hold up to two more homes. Steilacoom 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 Steilacoom allows.
The headline standards. Tap any one for the full wording and the code section.
ADUs per lot2Full wording
2 — one attached or detached ADU, 1 attached + 1 detached, 2 attached, or 2 detached in one or two structures, on lots that meet the zone's minimum lot size (SMC 18.16.020(b)(1)(C)).
Max size1,000 sq ft maximum gross floor areaFull wording
1,000 sq ft maximum gross floor area; 320 sq ft minimum (SMC 18.16.020(b)(1)(E)). No exclusions stated.
Max height26 ft — the R-7.2/R-9.6 maximum for all buildingsFull wording
26 ft — the R-7.2/R-9.6 maximum for all buildings (SMC 18.20.040(a)); no ADU-specific height. See Notes on the lower cap for accessory buildings near a rear lot line.
Front setback20 ft street setback in R-7.2 and R-9.6 (same as the house)Full wording
Same as principal: 20 ft street setback in R-7.2 and R-9.6; corner lots have two 20 ft street setbacks (SMC 18.16.020(b)(1)(B); 18.20.020(a), (f)).
Side setback5 ft each side, 20 ft combined (same as the house)Full wording
Same as principal: 5 ft minimum each side with a 20 ft combined total in R-7.2 and R-9.6; corner lots 5 ft on the one interior side (SMC 18.16.020(b)(1)(B); 18.20.020(a), (f)).
Rear setback20 ft in R-7.2 and R-9.6 (same as the house)Full wording
Same as principal: 20 ft in R-7.2 and R-9.6 (SMC 18.20.020(a)); 'Detached ADUs may be sited at a lot line if the lot line abuts a public alley' (SMC 18.16.020(b)(1)(B)(i)).
Lot coverage30% building, 50% imperviousFull wording
30% building coverage and 50% impervious surface in R-7.2 and R-9.6 (SMC 18.20.030(a)); ADUs may not exceed allowable lot coverage (SMC 18.16.020(b)(1)(B)).
Parking1 extra off-street space per ADUFull wording
1 additional off-street space per ADU, on top of the single-family dwelling's required parking (SMC 18.16.020(b)(2)).
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 are a secondary use in the R-7.2 and R-9.6 residential zones (SMC 18.12.030 table) and may be attached or detached, including two detached units in one or two structures (SMC 18.16.020(b)(1)(C); Ord. 1690, eff. 1/1/2024).
Minimum lot size
ADUs only on lots meeting the zone minimum (SMC 18.16.020(b)(1)(C)): R-7.2: 7,200 sq ft; R-9.6: 9,600 sq ft (SMC 18.20.030(a)).
Do you have to live there?
No — SMC 18.16.020 (Ord. 1690, eff. 1/1/2024) contains no owner-occupancy requirement.
Can it be sold on its own?
Yes — 'Nothing in this section prohibits the sale or other conveyance of a condominium unit independently of a principal unit solely on the grounds that the condominium unit was originally built as an accessory dwelling unit' (SMC 18.16.020(b)(1)(F)).
Pre-approved plans
None found
How long the city takes
Not published
Impact fees
School impact fee for an accessory dwelling unit is $0.00 (SMC 15.30.190, Ord. 1738, eff. 1/1/2026); Title 15 has no park or traffic impact fee chapter.
Plans Steilacoom has already approved.
A pre-approved plan skips the design review: Steilacoom 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 Steilacoom 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 Steilacoom 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.
5 sources, read November 5, 2026
- www.townofsteilacoom.org/DocumentCenter/View/624 (SMC Title 18 PDF: 18.08.002, 18.08.918, 18.12.030, 18.16.010, 18.16.020, 18.20.020–.040)
- www.townofsteilacoom.org/DocumentCenter/View/605 (Ordinances Table)
- www.townofsteilacoom.org/DocumentCenter/View/621 (Title 15)
- www.townofsteilacoom.org/311/Middle-Housing
- RCW 36.70A.681 — the state floor for accessory dwelling units
Find out what your property could become.
Type your address. Within a few hours: what Steilacoom allows, what could fit, and a planning cost range. Free, no obligation.