Mich. Comp. Laws § § 125.489

Sec. 89.

Rooms, lighting and ventilation of. No room except water-closet compartments in a dwelling erected prior to the passage of this act shall hereafter be occupied unless it shall have a window or windows of an area equal to not less than 1/10 of the floor area opening directly upon the street, or upon a rear yard not less than 10 feet deep, or above the roof of an adjoining building, or upon a court located on the same lot with the dwelling or on an adjoining lot and having an area not less than 50 square feet and a minimum dimension not less than 3 feet and being open and unobstructed from the window sill to the sky, or upon a side yard located on the same lot with the dwelling or on an adjoining lot and having a minimum width not less than 2 feet, except that a room located on the top floor may be lighted by means of a skylight if the skylight has an area equal to not less than 1/10 of the floor area and is ventilated directly to the outer air by an opening or openings having an area equal to not less than 1 per cent of the floor area. A room which cannot be made to comply with the above provisions may be occupied if provided with a window having an area not less than 1/8 of the floor area of such room, 40 per cent of the area of which window shall be capable of being opened, opening into an adjoining room in the same apartment or group or suite of rooms which latter room has a window or windows of area equal to not less than 1/6 of the area of the larger of the 2 rooms involved, 40 per cent of the area of which windows shall be capable of being opened, opening directly on a street or on a rear yard of the above dimensions. In so far as possible the windows between the 2 rooms shall be in line with windows in the outer room so as to afford a maximum of light and ventilation.