Michigan Compiled Laws, Chapter 125. Planning, Housing and Zoning § 125.1513d

(a) “Stairwell geometry” refers to the configuration of a stairwell of a building in which the maximum riser height is 8- 1/4 inches (210 mm), the minimum tread depth is 9 inches (229 mm), and a 1-inch (25 mm) nosing on stairwells with solid risers.

(b) “Use group R-2 structures” means all multiple-family dwellings having more than 2 dwelling units including, but not limited to, boarding houses and similar buildings arranged for shelter and sleeping accommodations in which the occupants are primarily not transient in nature and dormitory facilities that accommodate more than 5 persons over 2- 1/2 years of age.

(c) “Use group R-3 structures” means all buildings arranged for occupancy as 1-family or 2-family dwelling units including, but not limited to, not more than 5 lodgers or boarders per family; multiple single-family dwellings where each unit has an independent means of egress and is separated by a 2-hour fire separation assembly; and a child care facility that accommodates 5 or less children of any age.