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(1) As used in this subchapter, the following definitions apply:

(a) "Accessory structure" means a building or structure utilized for sheltering equipment or materials, or for other uninhabitable occupancy purposes.

(b) "Approved" means acceptable to the code official or authority having jurisdiction.

(d) "Fire-resistance-rated construction" means the use of methods, materials, and systems in the construction of a structure to provide against the spread of fire within a structure and to or from a structure to the outside environment.

(e) "Ignition-resistant building material" means a type of building material that resists ignition or sustained flaming combustion.

(f) "International Building Code" means the International Building Code (IBC), adopted by ARM 24.301.131.

(g) "International Residential Code" means the International Residential Code (IRC) adopted by ARM 24.301.154.

(h) "Noncombustible" means a material that is either a material of which no portion will ignite and burn when fire is applied to it, or a material that has a structural base of noncombustible material with surface materials not in excess of 1/8 inch in thickness, which has a flame spread index of 50 or less.

(i) Any material conforming to ASTM 136 shall be considered noncombustible.

(ii) "Flame spread index" refers to the index obtained from tests conducted in ASTM E 84 or UL 723.

(i) "Wildland-Urban Interface" (WUI), means the line, area, or zone where structures and other human development meet or intermingle with undeveloped wildland or vegetative fuels.

(1) For the purposes of this subchapter and pursuant to 50-60-901, MCA, the department provides the following construction techniques that may be used individually or in combination by a local government to mitigate identified fire hazards in areas designated by local government pursuant to 76-3-504, MCA.

(2) Rules adopted under this subchapter may not be construed as part of the state building code provided in 50-60-203, MCA, and may only be enforced as provided in Title 76, chapter 3, part 5.

(1) The address of the building shall be plainly visible and legible from the building's primary access road adjacent to the property.

(1) All habitable structures shall have smoke alarms installed that meet or exceed the provisions for smoke detection and notification found in either the latest adopted edition of the IRC or the IBC, whichever applies to the type of structure.

(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.

(1) An approved spark arrester constructed of a minimum 12-gauge welded-wire or woven-wire mesh, with openings not exceeding 1/2 inch shall be installed on every fireplace and wood stove chimney and flue.

(1) Gutters and downspouts shall be constructed of noncombustible materials and shall prevent the accumulation of leaves and debris by an approved method.

(2) If a structure is not located in a designated WUI, this rule does not apply.

(1) In structures where the window to exterior wall area exceeds 20 percent (i.e., more than 20 percent of all exterior wall areas is comprised of exterior windows or window walls), the exterior windows, window walls, glazed doors, glazing within exterior doors, and skylights shall be tempered glass, multilayered glazed panels, glass block, or have a fire protection rating of not less than 20 minutes.

(2) Exterior doors shall be of approved noncombustible construction and materials, solid core wood not less than 1 3/4 inches thick, or have a fire protection rating of not less than 20 minutes. Vehicle access doors shall be constructed of ignition-resistant building materials.

(3) Exterior walls of buildings or structures shall extend from the top of the foundation to the underside of the roof sheathing and shall be constructed with one of the following methods:

(a) materials approved for a minimum of one-hour fire-resistance-rated construction on the exterior side;

(b) noncombustible materials;

(d) wood that is labeled for exterior use and is fire-retardant-treated on the exterior side; or

(e) materials that are ignition-resistant on the exterior side.

(4) If a structure is not located in a designated WUI, this rule does not apply.

(1) Ventilation openings in vertical exterior walls, attics, foundations, or underfloor areas shall not exceed 144 square inches each. Attic ventilation openings shall not be located in soffits, eave overhangs, between rafters at eaves, or other overhang areas.

(a) Gable end and dormer vents shall be located at least ten feet from property lines.

(b) Underfloor ventilation openings shall be located as close to grade as practical.

(2) All such vents shall be covered with noncombustible corrosion-resistant mesh with openings not to exceed 1/4 inch or shall be designed and approved to prevent ember or flame penetration into the structure. Vents shall not be placed in walls that face heavy vegetative fuels.

(3) If a structure is not located in a designated WUI, this rule does not apply.

(1) All underfloor areas shall be enclosed to the ground in the same manner as required for exterior walls in ARM 24.321.308, unless such unenclosed areas are protected with either one-hour fire-resistance-rated construction or heavy timber construction or fire-retardant-treated wood to the underside of all exposed floors and all exposed structural columns, beams, and supporting walls.

(2) If a structure is not located in a designated WUI, this rule does not apply.

(1) An accessory structure without a complete exterior wall system enclosing the area under the roof or above the floor that is attached to buildings with habitable spaces and projections (e.g., decks), shall be a minimum of one-hour fire-resistance-rated construction, heavy timber construction, or constructed of one of the following:

(a) noncombustible materials;

(b) fire-retardant-treated wood labeled for exterior use; or

(2) When an attached accessory structure is located so that any portion of the structure projects over a descending slope surface greater than ten percent, the area below the structure shall have all underfloor areas enclosed to within six inches of the ground, with exterior wall construction in accordance with ARM 24.321.308.

(3) If a structure is not located in a designated WUI, this rule does not apply.

(1) Propane tanks and other flammable or combustible liquids storage shall be buried underground. If soil or subsoil conditions prohibit complete burial, then tanks shall be partially covered by at least one foot of earth, sand, or other noncombustible material.

(2) Other installation methods such as installation in vaults or other protective methods that comply with NFPA 30 and NFPA 58 standards may be used in lieu of burial.

(3) Structures not located in a designated WUI may have storage tanks installed above ground, so long as they conform to the NFPA 58 standard and be located at least 30 feet from any structure.