What's Required in Milwaukee
- Only one accessory dwelling unit is allowed per parcel.
- At least one owner must occupy the existing house as a primary residence when the permit application is submitted.
- Internal and attached ADUs require a single-family house; detached ADUs may accompany a single- or two-family house.
- Every ADU needs at least 300 sq ft; internal and attached units may not exceed 1,000 sq ft.
- Detached ADUs may not exceed 1,300 sq ft or 16% of the lot (whichever is greater), capped at 1,600 sq ft and the size of the largest unit.
- Detached ADUs need 3-foot side and rear setbacks and 10-foot front-to-back separation from the house.
- Plans must meet the Wisconsin Uniform Dwelling Code and Milwaukee's building and zoning codes; detached units need site utility plans.
- Electrical permits must be pulled by a licensed electrician; plumbing by the homeowner or a licensed plumber.
Can you build an ADU in Milwaukee?
Yes. Milwaukee's zoning code lists the accessory dwelling unit as a limited use in every residential district, and the current standards (table 295-505-2.5, in effect since August 2, 2025) allow three types: an internal unit inside the house, an attached unit in an addition, and a detached unit in its own building. The conditions in MCO 295-505-5-f are short:
- Only one ADU per parcel.
- Internal and attached ADUs need a single-family house on the parcel; a detached ADU may go with a single-family or two-family house.
- Owner occupancy: when you apply for the building permit, at least one owner must live in the existing house as a primary residence, shown by 2 documents such as a driver's license, voter registration, tax return or utility bill. The rule does not apply when the ADU and a new house are built at the same time. Miss any of these and the ADU is a prohibited use.
How big can a Milwaukee ADU be?
Every ADU must have at least 300 sq ft. Internal and attached units are capped at 1,000 sq ft and must be smaller than the largest dwelling unit; an internal unit must also sit on one level. A detached unit may have 1,300 sq ft of habitable and parking area, or 16% of the lot area if that is greater, but never more than 1,600 sq ft or the size of the largest dwelling unit. It may be no taller than the house, needs 3-foot side setbacks, a 3-foot rear setback (4 feet from an alley if it has an alley-facing garage door), and must sit 10 feet front-to-back and 5 feet side-to-side from the house, with a paved walk to the street. DNS's ADU sheet still prints a flat 1,300 sq ft cap for detached units; the code allows more on large lots.
How much are ADU permits in Milwaukee?
A detached ADU is billed as new one- or two-family construction: $0.55 per sq ft building permit ($200 minimum), $0.25 per sq ft plan review ($175 minimum), the $65 energy code fee, and erosion control ($250 per lot plus $175 plan review). An internal conversion is an alteration: 1.6% of construction cost plus $0.25 per sq ft review. DNS adds 1.6% to those fees, each permit has a $20 to $25 processing fee, and the city assessor's MCO 81-6 service charge is $450 per new dwelling unit or $250 for an alteration. Electrical, plumbing and HVAC permits are separate.
- 600 sq ft basement ADU, $45,000 of construction: building side $1,153.92; electrical $192.64; plumbing $106.36; ductwork $75.80. Total $1,528.72.
- 800 sq ft detached ADU: building, review, energy and erosion fees $1,188.08 with surcharge and processing, plus $450 assessor; electrical $375.52; plumbing $223.20; HVAC $192.64. Total $2,429.44.
| What you are doing | City filing | Rule |
|---|---|---|
| Internal ADU (basement or attic) | Alteration permit, 1.6% of cost + review | Single-family house; owner lives on site |
| Attached ADU in an addition | Addition permit, $0.55/sq ft + review | Up to 1,000 sq ft; single-family house |
| Detached ADU | New construction permit + erosion control | 1,300 sq ft or 16% of lot, max 1,600 |
| Second ADU on the same parcel | Not allowed | MCO 295-505-5-f-1 |
| ADU when no owner lives on site | Prohibited use | Unless built together with a new house |
| Wiring the ADU | Electrical permit by a licensed electrician | MCO 222; DNS ADU sheet |
| Plumbing and site utilities | Plumbing permit; site utility plans for detached | Homeowner or licensed plumber |
The building permit may be taken out by the homeowner or by a contractor licensed by the State of Wisconsin and the City. Bring three copies of plans; detached units also need separate site utility plans.
How to Get a ADU Permit in Milwaukee
Confirm eligibility
Check that the parcel has the right house type, no existing ADU, and that an owner lives in the house and can document it.
Size and site the unit
Fit the unit within the floor area caps, height limit, setbacks and separation distances in table 295-505-2.5.
Prepare plans
Have plans drawn to the Uniform Dwelling Code with energy calculations; detached units also need site utility and erosion control plans.
Submit for plan review
Submit three copies at the Permit and Development Center, 809 N. Broadway, or through the Land Management System, and pay plan review fees first.
Pull trade permits and build
Pay the building permit, have licensed trades pull electrical, plumbing and HVAC permits, start within 180 days and pass final inspections.