Can I build a backyard home on my lot in Washington?
Since 2023, Washington law has set a floor for accessory dwelling units inside urban growth areas: at least two per lot, at least 1,000 square feet, no owner-occupancy rule, condominium sale allowed. Your city writes its own rules on top — and if it isn’t on our list yet, the floor is what the report starts from.
What Washington allows.
The floor every city must meet. A city may be more generous, never stricter (RCW 36.70A.681).
ADUs per lotAt least 2 per lotFull wording
At least 2 (1 attached + 1 detached, 2 attached, or 2 detached)
Max sizeAt least 1,000 sq ft must be allowedFull wording
May not cap below 1,000 sq ft
Max heightAt least 24 ft must be allowed (unless the main house is capped lower)Full wording
May not cap below 24 ft, unless the principal-unit limit is lower
Front setbackNo stricter than for the main houseFull wording
May not be more restrictive than for principal units
Side setbackNo stricter than for the main houseFull wording
May not be more restrictive than for principal units
Rear setbackNo stricter than for the main house; 0 ft at an alleyFull wording
May not be more restrictive than for principal units; DADUs allowed at alley lot lines unless the alley is routinely plowed
Lot coverageNo stricter than for the main houseFull wording
Yard coverage limits may not be more restrictive than for principal units
ParkingNone within ½ mile of a major transit stop; at most 1–2 spaces elsewhereFull wording
0 within 1/2 mile of a major transit stop; max 1 space/unit on lots under 6,000 sq ft; max 2 on lots over 6,000 sq ft
Does not apply outside urban growth areas, or to lots with critical areas or their buffers.
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 — must be allowed in zones that allow single-family homes, inside urban growth areas
Minimum lot size
Must allow an ADU on any lot meeting the minimum lot size for the principal unit
Do you have to live there?
Prohibited as a requirement
Can it be sold on its own?
May not prohibit sale of a condominium unit solely because it was built as an ADU
Pre-approved plans
State has no plan program; SHB 1353 (2025) lets cities create optional architect self-certification for detached ADUs
How long the city takes
n/a — see each jurisdiction
Impact fees
ADU impact fees capped at 50% of the principal-unit fee; public street improvements may not be required
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 Washington 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 Revised Code of Washington 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 your city.
Find out what your property could become.
Type your address. Within a few hours: what Washington allows, what could fit, and a planning cost range. Free, no obligation.