Building an ADU

[Aidan Birmingham]

I have found a duplex that has about 1250 sqft of an empty land next to it. The lot is zoned as RT4. My idea was to build a single family ADU since I researched that the you need 1200 sqft of land per unit and the lot is .1 acre (4356sqft) so the lot can only allow one more unit.
how much would it roughly cost to build a 2 or 3 bed adu?

[Marcus Auerbach]

About $250 to $300 per square foot, because it is small which drives the per sqft cost up absorbing kitchen, bathroom, plumbing, electrical, utilities, basement, roof and impact fees into a small footprint. Bedrooms are cheap.

We will likely see zoning law changes in 2025 for the city of Milwaukee that will lift restrictions on ADU's (google GrowingMKE).