New Berlin, WI Accessory Structures: ADU Rules (2026)

Sec. 275-42 C governs accessory dwelling units in New Berlin's Zoning Code, and it draws a sharp line between commercial and residential districts. In the B-2, B-3 and B-5 business districts, subsection C(1) allows residential quarters in the same building as the business itself, provided the unit meets the minimum floor area requirements of the Rm-1 Zoning District, adequate off-street parking and roadway access are provided, and there is sufficient yard space for ordinary outdoor activity. Subsection C(2) separately permits caretaker or clergy residential quarters in the 1-1 Institutional District.

In agricultural and single-family residential districts, subsection C(3) instead authorizes what the code calls a family dwelling unit or 'in-law suite,' with detached accessory dwelling units expressly prohibited: the unit must be attached and architecturally integrated with the principal dwelling, requires its own zoning permit under Sec. 275-24, can be built with a new home or added later, and requires the owner to live on the property in either the principal or the family unit. Occupancy is restricted to relatives connected to the owner by blood, adoption, marriage or another legally recognized relationship, enforced by a recorded deed restriction, and capped at two occupants.

Size is limited to no more than 50% of the principal unit's living space, and while a separate entrance is allowed, it cannot face the front of the principal dwelling, and the unit needs at least one interior connection to the main house. Notably, Sec. 275-42 B(1)(a)[2][b][iii] separately bars placing an ADU or living quarters inside a detached accessory building in single-family and two-family districts, closing off using a garage or pole barn as a workaround.