Milwaukee’s accessory-dwelling-unit guidance separates internal, attached, and detached ADUs because their size and site rules differ. It describes where an ADU may be considered, a general limit of one per property, and other conditions tied to the principal residence. Use the City’s current zoning map and code to confirm that the property and proposed form qualify; the summary table is not a parcel determination.

Compare the published floor-area limits

The City’s guide lists a 300 sq ft minimum for all three forms. Internal and attached ADUs generally have a 1,000 sq ft ceiling and cannot exceed the largest dwelling’s area. Internal units also have one-level and first-floor-area conditions, with an exception described for certain structures that existed on August 2, 2025. Read those conditions in the City’s current guidance before using the headline number.

For a detached ADU, the guide allows the greater of 1,300 sq ft of habitable and parking area across all levels or 16% of lot area, subject to a cap of 1,600 sq ft or the floor area of the largest dwelling, whichever is lower. The guide also says a detached ADU may not be taller than the principal building. These calculations depend on the City’s definitions and the exact building configuration.

Check setbacks and building spacing

The published detached-ADU table lists a side setback of 3 ft. Its rear setback is 4 ft where a garage overhead door faces the alley and 3 ft otherwise; the front setback cannot be less than the principal building’s. Minimum building separation is 10 ft front-to-back or 5 ft side-to-side. ADUs in rear or side yards also need the stated paved walkway or access drive to street frontage.

Milwaukee’s page is planning guidance, not the complete zoning code. District, lot coverage, overlays, historic-preservation review, existing conditions, and any variance process can change the result. Confirm the current ordinance, site measurements, and design-specific conditions with the City. Zoning spacing does not establish fire separation, accessibility, structural safety, utility service, or permit approval.