How close to my side lot line can I build an addition in Sterling Heights?

It depends on your district. In R-80, R-70, and R-60, the least side yard is 5 feet with 15 feet total across both sides. In R-90 it is 8 feet and 20 total, and in R-100 it is 10 feet (8 with a side-entry garage) and 25 total (Section 3.04.A.6.b). In R-2 it is 10 feet and 20 total (Section 4.04.A.4.b). Where a side-entry garage faces the side lot line, its door must sit at least 22 feet from that line (Section 3.04.A.6.b).

An attached addition or garage must meet the same setbacks as the house (Section 28.00.A). Small projections get relief: eaves, gutters, and chimneys may project 2 feet into a required side yard, but Section 28.10.A expressly excepts bay windows from the side yard projection. An as-built structure matching its approved plot plan may encroach up to 6 inches without a variance (Section 28.10.D).

Rear setbacks are 35 feet in most districts, 40 in R-100, with decks allowed to project 15 feet into the rear yard under conditions (Section 3.04.A.6.c; Section 28.10.C). If the math does not work, a non-use variance from the Zoning Board of Appeals is the path (Section 30.02.C.6.a).