Can I build a backyard home in Auburn?
Since 2023, Washington law lets most city lots hold up to two more homes. Auburn 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 Auburn allows.
The headline standards. Tap any one for the full wording and the code section.
ADUs per lot2 per residential unitFull wording
2 per residential unit, attached, detached or any combination, on individually owned lots that meet the zone's minimum lot size (ACC 18.32.010(B)-(C)).
Max size1,000 sq ft maximumFull wording
1,000 sq ft maximum; 300 sq ft minimum; no more than 2 bedrooms. Garage space is not counted (ACC 18.32.010(D)).
Max height24 ft (the accessory-building cap in R-2 to R-4)Full wording
24 ft — the cap on accessory buildings and structures in R-2, R-3 and R-4 (ACC Table 18.07.030, row H); ACC 18.32.010 sets no separate ADU height.
Front setback10 ft in R-2 (same as the house)Full wording
Same as principal: 10 ft in R-2; a garage needs 20 ft from the street access (ACC Table 18.07.030, rows E1–E2).
Side setback5 ft interior side setback in R-2Full wording
5 ft interior side setback in R-2 (ACC Table 18.07.030, row E5).
Rear setback10 ft for a detached structure in R-2Full wording
10 ft for a detached structure in R-2 (15 ft for the residence) (ACC Table 18.07.030, rows E7–E8). Where the lot abuts a public alley that the city does not routinely plow, a detached ADU may sit in the rear setback, on the lot line (ACC 18.32.010(I); Table 18.07.030 note 8).
Lot coverage75% maximum impervious area in R-2Full wording
75% maximum impervious area in R-2 (ACC Table 18.07.030, row F); the table has no separate building-coverage cap.
Parking1 per ADU; none within ½ mile of major transitFull wording
1 space per ADU beyond 1/2 mile walking distance of a major transit stop; 0 spaces within it (ACC 18.32.010(F)).
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 — permitted outright in all residential zones that allow single-unit detached or middle housing; attached, detached or any combination (ACC 18.32.010(A), (C)).
Minimum lot size
None separate for an ADU; the lot must meet the zone's minimum lot size (ACC 18.32.010(B); ACC Table 18.07.030)
Do you have to live there?
No — ACC 18.32.010 (Ord. 6959) has no owner-occupancy requirement; it only requires a recorded notice to future owners (ACC 18.32.010(K)(2)).
Can it be sold on its own?
Yes — an ADU may be sold as a condominium unit or as separate property through a unit lot subdivision; separate water and sewer connections are then required (ACC 18.32.010(G)).
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 Auburn has already approved.
A pre-approved plan skips the design review: Auburn 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 Auburn 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 Auburn 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 Auburn allows, what could fit, and a planning cost range. Free, no obligation.