Cities · Snohomish County

Can I build a backyard home in Snohomish County (unincorporated)?

Since 2023, Washington law lets most city lots hold up to two more homes. Snohomish County (unincorporated) 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.

Read from the Snohomish County (unincorporated) code on October 8, 2026 · confidence high · a summary, not legal advice. Rules change; the report re-reads them for your parcel.

The short version

What Snohomish County (unincorporated) allows.

The headline standards. Open any card for the full wording and the code section.

ADUs per lot2 per urban single-family lot; 1 ruralFull wording

Urban: 2 per single-family dwelling (1 attached + 1 detached, 2 attached, or 2 detached). Single-family attached: 1. Duplex: 2. Rural and resource: 1.

Max size1,200 sq ft of floor area, excluding garages, porches, unheated storage and unfinished basementsFull wording

1,200 sq ft of floor area, excluding garages, porches, unheated storage and unfinished basements

Max heightThe zone height: 30 ft in R-9,600 / R-8,400, 35 ft in R-7,200Full wording

No ADU-specific height in SCC 30.28.010; the zone height applies — urban residential (Table 30.23.032): R-9,600 30 ft, R-8,400 30 ft, R-7,200 35 ft, LDMR 45 ft; rural R-5 45 ft (Table 30.23.030); +5 ft for a daylight basement (30.23.040 note 16)

Front setback10 ftFull wording

10 ft (R-9,600 / R-8,400 bulk matrix)

Side setback5 ftFull wording

5 ft (R-9,600 / R-8,400 bulk matrix)

Rear setback5 ftFull wording

5 ft (R-9,600 / R-8,400 bulk matrix). 5 ft from private roads; 5 ft from public roads 60 ft or wider or in recorded subdivisions; otherwise the lesser of 35 ft from centerline or the averaged setback.

Lot coverage55% on an urban lot with an ADUFull wording

55% on an urban lot with an ADU (base 35% in R-9,600 / R-8,400 / R-7,200; 50% in LDMR / MR)

ParkingNone in urban zones; 1 space in rural zonesFull wording

None in urban residential zones; 1 space per ADU in rural and resource zones

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.

The rest

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

Urban: must meet the minimum lot size for the principal unit. Rural: no DADU on a lot below the zone minimum; R-5 lots under 5 acres and RC lots under 100,000 sq ft cannot have a DADU. Split-zoned parcels per Director's Rule 24-07, effective June 11, 2025.

Do you have to live there?

No — not required

Can it be sold on its own?

Yes — permitted; the 'under the same ownership' language was removed

Pre-approved plans

In development as of July 2026. No county catalog is published yet.

How long the city takes

SCC 30.70.110: 65 calendar days without notice of application, 100 days for Type 1 with notice, 170 days for Type 2 — measured from a complete application and excluding correction periods. The county states no liability for missing these.

Impact fees

School impact fees: ADUs exempt — 'Permits for attached or detached accessory dwelling units' (SCC 30.66C.010(2)(b)). Traffic (SCC 30.66B.330): a per-new-daily-trip fee by transportation service area (inside UGA $185–$736 per trip), no dwelling-type line — the ADU trip rate comes from the transportation needs report; parks (SCC 30.66A.040, Ord. 25-068, Dec. 2025): single-family $685.22 (2 bedrooms or fewer) / $831.94 (3+) in most park service areas, multifamily $339.04 / $660.01, no ADU category. No county 50% ADU rule found; the RCW 36.70A.681 cap applies

Your lot

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.

Free, within a few hours, no obligation.
What Snohomish County (unincorporated) 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.

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Sources

Where this page comes from.

Read from the Snohomish County (unincorporated) municipal code and the city’s own pages on October 8, 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 county.

Nearby

Other places in Snohomish County.

Edmonds 1,200 sq ft Everett Under 1,000 sq ft by definition Lake Stevens 1,000 sq ft gross floor area Lynnwood 1,000 sq ft Marysville 1,000 sq ft or 50% of the residence, whichever is greater, capped at 1,400 sq ft Mill Creek 1,000 sq ft All cities →

Find out what your property could become.

Type your address. Within a few hours: what Snohomish County (unincorporated) allows, what could fit, and a planning cost range. Free, no obligation.

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