Mich. Comp. Laws § 125.1524

Sec. 24. Until 6 months after promulgation of the code, construction regulations heretofore or hereafter adopted by a governmental subdivision continue in effect unless repealed by local law or ordinance. Six months after the promulgation of the code and thereafter, construction regulations adopted by a governmental subdivision shall be considered repealed and invalid, except as provided in section 8. A building permit validly issued under local construction regulations within 6 months before promulgation of the code is valid, and the construction of a building or structure may be completed pursuant to that building permit. The construction of a building or structure started before promulgation of the code in an area of the state that did not as of the date of beginning of construction require a building permit may be completed without a building permit. Except as provided in section 28, construction regulations incorporated in any act of this state in effect or validly promulgated by any board, department, commission, or agency continue in effect until promulgation of the code at which time they shall be considered to be superseded.