Administrative Rules of Montana
Department 24 - LABOR AND INDUSTRY
Chapter 24.301 - BUILDING CODES
Subchapter 24.301.1 - Adoption and Incorporation by Reference of Uniform and Model Codes Having General Applicability
Rule 24.301.154 - INCORPORATION BY REFERENCE OF INTERNATIONAL RESIDENTIAL CODE

(1) The International Residential Code (IRC) is a nationally recognized model code setting forth minimum standards and requirements for detached one- or two-family dwellings and multiple single-family dwellings (townhouses) not more than three stories above grade in height, and their accessory structures. The IRC also provides a framework for program administration.

(2) The department adopts and incorporates by reference the International Residential Code, 2021 edition, referred to as the International Residential Code or IRC, together with:

(3) Chapters 11 through 14, inclusive, are deleted in their entirety and chapters 16 through 43, inclusive, are deleted in their entirety. Chapter 15, Exhaust Systems, is adopted as an alternative to the International Mechanical Code for exhaust systems only. All other requirements for mechanical systems in detached one- or two-family dwellings and multiple single-family dwellings (townhouses) not more than three stories above grade in height, and their accessory structures, shall be found in the latest adopted edition of the International Mechanical Code.

(4) Subsection R102.7, Existing Structures, is deleted and replaced with the following: "The legal occupancy of any structure existing on the date of this code shall be permitted to continue without change, except as is specifically covered in this code or the legally adopted fire code as administered by the fire authority having jurisdiction."

(5) Subsection R301.6, Roof Load, is deleted and replaced with the following: "Snow loads shall be determined by the building official. In areas of the state outside of certified city, county, or town jurisdictions, the design snow load shall be based on the ground snow loads calculated using the 2022 edition of the American Society of Civil Engineer's "Minimum Design Loads and Associated Criteria for Buildings and Other Structures, ASCE/SEI 7-22." The information is available online using the "ASCE 7 Hazard Tool" at https://asce7hazardtool.online/. The minimum design roof snow load after allowed reductions shall be 30 psf unless justified by a Montana licensed design professional to the satisfaction of the building official. Coefficients and factors other than those specified in the building code may be used when justified by a Montana licensed design professional to the satisfaction of the building official."

(6) Subsection R302.2.2, Common walls, delete "Chapters 34 through 43" and replace with "the adopted electrical code in ARM Title 24, chapter 301, subchapter 4."

(7) Subsection R302.2.6, Structural Independence, delete exception number five and replace with the following: "Townhouses separated by a common two-hour fire-resistance-rated wall as provided in Section R302.2."

(8) Subsection R302.13, Fire Protection of Floors, is deleted in its entirety.

(9) Subsection R309.5, Fire Sprinklers, is deleted in its entirety.

(10) Subsection R311.7.5.1, Risers, is amended to allow a maximum riser height of 8 1/4 inches.

(11) Subsection R311.7.5.2, Treads, is amended to allow a minimum tread depth of nine inches.

(12) Subsection R312.1.1, Where Required, delete the first sentence and replace with the following: "Guards shall be located along open-sided walking surfaces, including stairs, ramps, and landings, that are located more than 30 inches measured vertically to the floor or grade below."

(13) Section R313, Automatic Fire Sprinkler Systems, is deleted in its entirety.

(14) Subsection R403.1.1, Minimum size, is modified to add the following: "Exception: The building official may allow footings to be designed in accordance with Section R403 of the 2012 IRC or may allow footings engineered by a design professional."

(15) Subsection R403.1.6, Foundation Anchorage, is deleted in its entirety and replaced with the following: "Where wood sill and sole plates are supported directly on continuous foundation walls or monolithic slabs with integral footings required by the provisions of this code, they shall be anchored to the foundation in accordance with this section. Cold-formed steel floor and wall framing shall be anchored to the foundation in accordance with Section R505.3.1 or R603.3.1. Wood sole plates at all exterior walls, wood sole plates of braced wall lines at building interiors on monolithic slabs with integral footings and all wood sill plates shall be anchored to the foundation with minimum one-half inch diameter anchor bolts spaced a maximum of six feet on center or approved anchors or anchor straps spaced as required to provide equivalent anchorage to the one-half inch diameter anchor bolts. Bolts shall extend a minimum of seven inches into concrete or grouted cells of concrete masonry units. A nut and washer shall be tightened on each anchor bolt. There shall be a minimum of two bolts per plate section with one bolt located not more than 12 inches or less than seven bolt diameters from each end of the plate section. Interior bearing wall sole plates on monolithic slab foundations with integral footings that are not part of a braced wall line shall be positively anchored with approved fasteners. Sill plates and sole plates shall be protected against decay and termites where required by sections R317 and R318.

Exceptions:

(16) Subsection R405.1 is amended by adding the following: "A drainage system is not required when continuous rain gutters are installed incorporating drain extensions which divert storm water a minimum of six feet (1.83 m) away from the foundation and grading is done in accordance with R401.3. A drainage system may be required where high water tables are known to exist or geological conditions which require a soils engineering report, performed in accordance with R401.4, specify the need for foundation drainage."

(17) Subsection R602.10, Wall Bracing, delete the first sentence and replace with the following: "Building shall be braced in accordance with this section or, when applicable, Section R602.12, or the most current version of APA System Report SR-102 as an alternate method.

(18) Subsection R602.10.10, Cripple Wall Bracing, add the following sentence: "The distance between adjacent edges of braced wall panels shall be 20 feet."

(19) Subsection R703.4, Flashing, delete the first paragraph in its entirety and replace with the following: "Flashing shall be provided in accordance with this section to prevent entry of water into the wall cavity or penetration of water to the building structural framing components. Flashing shall extend to the surface of the exterior wall finish or to the water-resistive barrier for drainage and shall be installed at all of the following locations:"

Further, delete Number "1", number "1.1", number "1.2", and number "1.3" in their entirety and replace with the following: "1. Exterior window and door openings."

Number "2" through "7" remain unchanged in Subsection R703.4.

(20) Replace subsection R703.4.1 as follows: "R703.4.1, Flashing Materials. Approved flashing materials shall be corrosion-resistant. Self-adhered membranes used as flashing shall comply with AAMA 711. Pan Flashing shall comply with Subsection R703.4.2. Installation of flashing materials shall be in accordance with Subsection R703.4.3.

(21) Add new subsection as follows: "R703.4.2, Pan Flashing. Pan Flashing installed at the sill of exterior window and door openings shall comply with this section. Pan Flashing shall be corrosion-resistant and shall be permitted to be pre-manufactured, fabricated, formed, or applied at the job site. Self-adhered membranes complying with AAMA 711 shall be permitted to be used as Pan Flashing. Pan Flashing shall be sealed or sloped in such a manner as to direct water to the surface of the exterior wall finish or to the water-resistive barrier for subsequent drainage."

(22) Add new subsection as follows: "R703.4.3, Flashing Installation. Installation of flashing materials shall be in accordance with one or more of the following methods:

(23) Subsection R905.1.2 is amended by deletion of the language "areas where there has been a history of ice forming along the eaves causing a backup of water as designated in Table R301.2" and insert "the State of Montana."

(24) Appendices do not apply to a certified city, county, or town building code jurisdiction unless specifically authorized or adopted by the department and adopted by the certified city, county, or town building code jurisdiction.

(25) A copy of the International Residential Code may be obtained from the International Code Council at www.ICCsafe.org.