Section R. 400.18653 - Interior finishRule 653.
(1) An interior finish shall be a class A or B finish, except that an interior finish in an individual room may be a class C finish for walls only.(2) A combustible finish material shall be applied to, or be furred out not more than 1 inch from, a noncombustible surface behind which the space is firestopped into an area that extends not more than 8 feet in any direction.(3) If a combustible interior finish comprises more than 10% of the aggregate wall and ceiling surface of any room or space, and if the finish material is more hazardous than permitted in the provisions of subrule (1) of this rule, then the combustible interior finish may be treated so as to comply with the provisions of subrule (1) of this rule, if the material is secured to the walls or ceilings as specified in subrule (2) of this rule.(4) If interior finish is more hazardous than class A, and if it is furred more than 1 inch from a noncombustible wall or ceiling surface, it shall be replaced with a noncombustible material or reinstalled to comply with the provisions of subrules (1), (2), and (3) of this rule.(5) Existing wood paneling or combustible acoustical interior finish in lobbies, waiting rooms, and office areas in existing buildings may remain if the rooms or areas are separated from the rest of the building by proper walls and fire doors.(6) In a completely sprinklered building where the basic material is class C and is installed to comply with the provisions of subrules (1), (2), (3), and (4) of this rule, further treatment is not required. However, where the basic material is more hazardous than class C and is installed to comply with the provisions of subrules (1), (2), (3), and (4) of this rule, it shall be surface treated on its exposed side whether or not the building is sprinklered.
(7) Class C interior finish in the form of wainscoting which extends not more than 5 feet above the floor and which is installed to comply with the provisions of subrules (1), (2), (3), and (5) of this rule, shall not be required to be surface treated.(8) Interior finish means the exposed interior surfaces of buildings including, but not limited to, fixed or moveable walls and partitions, columns, and ceilings. Doors, trim, the backing of shelving, cabinets, and wardrobes shall be included in the 10% permissible class C finish category.(9) The classification of interior finish materials as to their flame spread and smoke development shall be that of the basic material used without regard to subsequently applied paint or other covering, except where the paint or other covering is of such character or thickness or so applied as to materially affect the flame spread and smoke characteristics. Highly combustible material applications, such as lacquer or pyroxylin base materials, or unapproved wall coverings shall not be used.(10) Paints or coatings that contain plastics, polyesters, or epoxies may be used on noncombustible surfaces without proof of classification if they are not applied in excess of 8 mils total thickness.Mich. Admin. Code R. 400.18653