Montana first adopted a statewide building code in 1972 with the adoption of the ICBO Uniform Codes. The state's first energy code was the 1983 Model Energy Code (MEC). Montana adopted the appendix of Chapter 53 (Energy) referenced in the 1985 Uniform Building Code, which referenced the 1983 MEC.
Montana adopted several of the MEC editions and supplements in the late 1980s and early 1990s, including the 1991 MEC with reference the first Standard 90.1 edition, ASHRAE 90.1-1989.
The state adopted the 2003 IECC with minimal changes as the statewide energy code on September 3, 2004. Effective January 26, 2007, Montana has adopted the 2006 version of all the other I-Codes (including the IBC and IRC), but not the IECC.
In spring 2010, Montana adopted the 2009 IECC with state amendments. Following a public hearing in November 2009, the Montana Department of Labor and Industry (DLI) filed the final adoption notice to amend ARM 24.301.161 with the Secretary of State on March 15 with an effective date of March 26, 2010. The state's 46 local certified jurisdictions will have an additional 90 days to adopt the same code and edition for their jurisdictions. All other areas are under the jurisdiction of the State Building Codes Bureau.