Is there a minimum house size in Troy, Michigan?

Yes. Troy sets a minimum floor area for single-family homes by district (Section 4.06.C):

• R-1A and R-1B: 1,400 sq ft.
• R-1C: 1,200 sq ft.
• R-1D and R-1E: 1,000 sq ft.

So a new house in the larger-lot districts must be at least 1,400 sq ft, while the smaller-lot districts allow homes down to 1,000 sq ft.

Multiple-family units have their own per-unit minimums in the MF district: 600 sq ft for an efficiency or one-bedroom, 800 sq ft for two bedrooms, 1,000 sq ft for three, and 1,200 sq ft for four (Section 4.08).

If a planned home falls short of the minimum, the path is a dimensional variance from the Zoning Board of Appeals under the practical difficulties standard (Section 15.04.E). Confirm your district with the Planning Department at 248-524-3364.