Can I build a duplex in Novi?

Only in the right district. Two-family dwellings are a by-right use in the RT Two-Family Residential district (Section 3.1.6.B), and they are conspicuously absent from the RA and R-1 through R-4 one-family district use lists, so an ordinary subdivision lot cannot take a duplex.

Beyond RT, two-family dwellings built to the RT standards are permitted in the RM-1 and RM-2 multiple-family districts and the MH district (Section 3.1.7.B; Section 3.1.8.B; Section 3.1.9.B), allowed in the TC and TC-1 Town Center districts as residential dwellings meeting RM-1 or cluster standards (Section 4.82), and available in the NCC district as a special land use (Section 3.1.20.C).

In RT, plan on 30 foot front and 35 foot rear setbacks, sides of 10 feet with 20 feet total, 35 feet or 2.5 stories of height, 750 square feet per unit, and density capped at 4.8 units per acre; the district page lists 7,500 square feet of lot area without stating whether that is per unit or per two-family building, and the density cap governs either way, so confirm the lot size for your specific parcel with the Community Development Department at 248-347-0415 (Section 3.1.6.D).