Administrative Rules of Montana
Department 24 - LABOR AND INDUSTRY
Chapter 24.321 - WILDLAND URBAN INTERFACE FIRE MITIGATION
Subchapter 24.321.3 - Wildland Urban Interface Fire Mitigation
Rule 24.321.305 - ROOF AREAS

(1) Roof coverings shall have at least a Class B roof assembly or an approved noncombustible roof covering. If the profile of the covering is such that a space is present between the covering and the roof decking, the space at the eave ends shall be fire-stopped to prevent the entry of flames or embers; or have one layer of 72-pound mineral-surfaced, nonperforated cap sheet, complying with ASTM D 3909, and installed over the combustible decking.

(2) When roof valleys are present, valley flashing shall consist of not less than 0.019-inch (26-gauge galvanized sheet) corrosion-resistant metal installed over a minimum three-foot wide underlayment of one layer of 72-pound mineral-surfaced, nonperforated cap sheet, complying with ASTM D 3909, and installed over the entire running length of the valley.

(3) Eaves, soffits, and fascias that are combustible shall be enclosed with solid materials with a minimum thickness of 3/4 inch. Rafter tails shall not be left exposed, unless constructed of heavy timber materials.

(4) If a structure is not located in a designated WUI, the roof assemblies listed in this rule shall comply with the IRC.