Are ADUs or in-law suites allowed in Rochester Hills?

No, as far as the ordinance states. Chapter 138 has no accessory dwelling unit provisions. The term appears nowhere in the use table, the accessory structure article, or the definitions (§ 138-4.300, § 138-13.101). The residential use table lists one-family, two-family, attached, and boarding or rooming dwellings, plus dwellings in mixed-use buildings. A second dwelling unit on a one-family lot is not among them (§ 138-4.300). Reading that silence, treat a detached ADU, garage apartment, or granny flat as not permitted. That is an inference from the ordinance's silence, not an express ban.

An in-law suite that stays part of the house is different. Bedroom or kitchen facilities that are part of the principal dwelling and do not constitute a separate dwelling unit are permitted (§ 138-10.301).

The paths to a true second unit are rezoning or a use variance, which requires a showing of unnecessary hardship and a two-thirds ZBA vote after a final rezoning denial (§ 138-2.408).