Can I build a backyard home in Mukilteo?
Since 2023, Washington law lets most city lots hold up to two more homes. Mukilteo 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 Mukilteo allows.
The headline standards. Open any card for the full wording and the code section.
ADUs per lotMaximum 2 per single-family lotFull wording
Maximum 2 per single-family lot; none in cottage housing developments
Max size1,000 sq ft habitableFull wording
1,000 sq ft habitable
Max height24 ft (the zone height over a garage)Full wording
24 ft; units over a garage may use the zone height
Front setbackThe zone’s setbacksFull wording
Zone setbacks
Side setbackThe zone’s setbacksFull wording
Zone setbacks
Rear setbackThe zone’s setbacks; 0 ft at an alleyFull wording
Zone setbacks; 0 ft at an alley
Lot coverageThe zone’s standardsFull wording
Zone standards
ParkingPer MMC Ch. 17.56Full wording
Per MMC Ch. 17.56
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
Zone minimum applies
Do you have to live there?
Not addressed in MMC 17.30; prohibited as a requirement by state law inside the UGA
Can it be sold on its own?
Not addressed in MMC 17.30; permitted by state law
Pre-approved plans
None found
How long the city takes
not published yet — ask the city
Impact fees
not published yet — ask the city
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 Mukilteo 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 Mukilteo 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 Mukilteo allows, what could fit, and a planning cost range. Free, no obligation.