Can I build a duplex in Rochester Hills?

Not in the standard one-family districts. Two-family dwellings are not permitted in RE, R-1, R-2, R-3, or R-4 (§ 138-4.300, Table 4).

Where duplexes are allowed:

• RM-1, the multiple-family district. Two-family dwellings are permitted by right. A duplex needs at least 6,000 square feet of lot area per unit and 50 feet of lot width per unit (§ 138-6.100, § 138-6.101).
• R-5. Two-family dwellings are permitted, with 25 feet of lot width per unit, 50 feet per structure, and 6,000 square feet of lot area per unit (§ 138-6.700).

Putting a duplex on land zoned RE through R-4 would require rezoning or a use variance. A use variance needs a two-thirds ZBA vote under the unnecessary hardship standard, and it requires a final City Council denial of a rezoning first (§ 138-2.408).