Can I build a backyard home in Seattle?
Since 2023, Washington law lets most city lots hold up to two more homes. Seattle 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 Seattle allows.
The headline standards. Open any card for the full wording and the code section.
ADUs per lot2 per lot, any combination, including two DADUsFull wording
2 per lot, any combination, including two DADUs
Max size1,000 sq ft (1–2 bedrooms); 1,200 sq ft (3+)Full wording
1,000 sq ft (1-2 BR); 1,200 sq ft (3+ BR); up to 1,500 sq ft in LR zones with frequent transit
Max height32 ft in NR/RSL zones (+5 ft with a pitched roof)Full wording
32 ft in NR/RSL zones; pitched roof 4:12 or steeper may add 5 ft (SMC 23.44.012.B)
Front setbackNo more restrictive than for the principal unitFull wording
No more restrictive than for the principal unit
Side setback5 ft from lot lines not abutting an alleyFull wording
5 ft from lot lines not abutting an alley (SMC 23.42.022.E.2.a)
Rear setback5 ft; 0 ft at an alleyFull wording
5 ft; 0 ft at an alley
Lot coverage50% in NR zonesFull wording
50% in NR (60% for stacked flats / cottage housing). ADU floor area is exempt from FAR in NR zones (23.42.022.C.3).
ParkingNone requiredFull wording
None required
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
Minimum lot size
No ADU-specific minimum in the amended Ch. 23.44; zone minimums NR1 9,600 / NR2 7,200 / NR3 5,000 sq ft. Old 23.44.041 (3,200 sq ft / 25 ft wide / 70 ft deep) was repealed effective June 30, 2025.
Do you have to live there?
No — removed in the 2019 reforms; SDCI issues a Release of Owner Occupancy Covenant
Can it be sold on its own?
Yes — condominium ownership allowed in all situations (SMC 23.42.022.J)
Pre-approved plans
Yes — ADUniverse pre-approved DADU gallery. 10 plans, 197 permits issued, permitting 39% faster (PSRC, May 2025). Plan licensing up to $1,000 paid to the designer. A 2026 refresh gallery (750-1,500 sq ft) was due November 2026.
How long the city takes
Pre-approved plan 2-6 weeks; simple new single-family about 2 weeks to initial review, complex about 8 weeks; traditional DADU permits historically 4-8 months
Impact fees
Exempt from impact fees and from MHA contributions; street improvements not required. Illustrative 2025 fees on a $250,000 DADU about $11,779; 2025 median actual DADU fees $10,840. SPU introduced new wastewater and drainage system development charges effective Jan 1, 2026; ADU treatment not confirmed.
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 Seattle 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 Seattle municipal code and the city’s own pages on September 15, 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 Seattle allows, what could fit, and a planning cost range. Free, no obligation.