Section 116.425 - Deck coverings(a) Except as provided in this section, deck coverings used for leveling or finishing purposes in control spaces, stairway enclosures, passageways, accommodation spaces and service spaces must be noncombustible.(1) Materials approved under § 164.006 in subchapter Q of this chapter may be used in thicknesses not to exceed the approved thickness.(2) Combustible deck leveling and finishing materials which are not approved under § 164.006 in subchapter Q of this chapter may be used in a thickness not to exceed 9.5 millimeters (.375 inches).