Cities · Pierce and King counties

Can I build a backyard home in Milton?

Since 2023, Washington law lets most city lots hold up to two more homes. Milton 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.

The short version

What Milton allows.

The headline standards. Tap any one for the full wording and the code section.

ADUs per lot2Full wording

2 — 'Two ADUs shall be allowed per legal building lot as an accessory use to a detached single-family dwelling or one ADU to a duplex' (MMC 17.44.160(E)(1)). NR1/NR2 maximum 3 dwelling units per lot, reached with 'single-family residential with two ADUs or two-family dwellings with one ADU' (MMC 17.15A.010 note 1)

Max size1,000 sq ft gross floor areaFull wording

1,000 sq ft gross floor area — 'An ADU shall not exceed 1,000 square feet in gross floor area'; the director may allow more for an ADU on a single floor of an existing multi-story building. Minimum 300 sq ft of habitable floor area; maximum two bedrooms (MMC 17.44.160(F)(1)–(3))

Max height24 ftFull wording

24 ft — 'A detached ADU shall have a maximum building height of 24 feet; except that an ADU may be created as a second story over a detached garage if the structure does not exceed the height of the principal dwelling unit' (MMC 17.44.160(F)(4)). NR1/NR2 zone maximum 35 ft (MMC 17.15B.010)

Front setback20 ft in NR1 and NR2 (same as the house)Full wording

Same as principal: 20 ft minimum setback from right-of-way in NR1 and NR2 (MMC 17.15B.010). 'Setback requirements for an accessory dwelling unit shall be the same as the principal use' (MMC 17.20.040(C))

Side setback7.5 ft in NR1 and NR2 (same as the house)Full wording

Same as principal: 7.5 ft in NR1 and NR2 (MMC 17.15B.010; 17.20.040(C))

Rear setback25 ft in NR1Full wording

25 ft in NR1; 10 ft in NR2 — the table's 'Minimum Rear Setback: ADU' row, not the 7.5 ft accessory-structure rear setback (MMC 17.15B.010). No alley rule found in the MMC; RCW 36.70A.681 allows a DADU at an alley lot line unless the alley is routinely plowed

Lot coverage40% total structure coverage and 50% impervious surface in NR1Full wording

40% total structure coverage and 50% impervious surface in NR1; 50% and 60% in NR2 (MMC 17.15B.010). Accessory structures built before Jan. 1, 2025 may convert to an ADU even if over coverage or in setbacks (MMC 17.44.160(F)(5))

Parking1 per ADU bedroom; none near frequent transitFull wording

1 space per ADU bedroom — 'One additional off-street parking space is required for each ADU bedroom' (MMC 17.44.160(F)(8)). None within 1/2 mile of a stop with fixed-route service every 15 minutes for 5 peak hours on weekdays; lots under 6,000 sq ft have 'a minimum requirement of one parking spot per unit' (MMC 17.48.040 table, notes 2–3)

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 — 'Dwelling Unit, Accessory' is authorized (A) in NR1 and NR2, and in NC subject to MMC 17.29.040 (MMC 17.14.010 Table of Uses). ADU types are attached, internal and detached, meaning 'a stand-alone accessory structure' (MMC 17.44.160(B), Ord. 2105, 2025)

Minimum lot size

None for an ADU; zone minimum applies to new lots — 8,000 sq ft in NR1, 4,000 sq ft in NR2 (MMC 17.15A.010)

Do you have to live there?

No — MMC 17.44.160 has no owner-occupancy rule. The owner must record an affidavit or agreement as a deed restriction that notes the ADU and agrees to keep it to this section's standards (MMC 17.44.160(C)–(D))

Can it be sold on its own?

Not addressed; RCW 36.70A.681 floor applies

Pre-approved plans

None found

How long the city takes

Not published — the city FAQ says plan reviews are 'first in – first out' and depend on completeness and workload. ADUs are a Process Type I administrative decision (MMC 17.44.160(D))

Impact fees

'For the purpose of calculating school, traffic and park impact fees, an accessory dwelling unit shall be charged at 50 percent of the single-family rate per the adopted fee schedule' (MMC 17.44.160(I)); the city's ADU Handout repeats the 50% rate

Pre-approved plans

Plans Milton has already approved.

All Milton plans →

A pre-approved plan skips the design review: Milton 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.

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 Milton 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.

Check my property, free →

Sources

Where this page comes from.

Read from the Milton municipal code and the city’s own pages on November 6, 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.

9 sources, read November 6, 2026

Nearby

Other places in Pierce and King counties.

Bonney Lake 1,200 sq ft gross for a detached ADU, minimum 450 sq ft Buckley 1,250 sq ft Edgewood 1,000 sq ft, or 80% of the house if more, up to 1,600 Fife 1,000 sq ft Fircrest 1,000 sq ft Gig Harbor 1,200 sq ft All cities →

Find out what your property could become.

Type your address. Within a few hours: what Milton allows, what could fit, and a planning cost range. Free, no obligation.

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