Montana Residential Code Compliance Evaluation

The Northwest Energy Efficiency Alliance (NEEA) contracted with Industrial Economics, Incorporated (IEc) to conduct a residential code compliance evaluation in Montana that examined new construction single family homes built under the International Energy Conservation Code (IECC) 2018 and 2021 with Montana amendments. The main study objective was to assess statewide compliance with the 2018 and 2021 IECC with Montana amendments. Additional objectives were to provide statewide findings regarding the proportion of homes with gas versus electric primary space heating, the proportion of homes with gas versus electric water heating, and the proportion of homes with above-code elements. Lastly, the report identified opportunities to increase compliance with the code.

From May 2024 to March 2025, IEc conducted on-site audits at 143 homes. Energy modeling analysis conducted by subcontractor Resource Refocus indicates that 86.1% of homes built under IECC 2018 with Montana amendments and 84.7% of homes built under IECC 2021 with Montana amendments comply with the code. The study also found that 86.5% of homes built under IECC 2021 with Montana amendments have gas primary space heating, while 40.2% of homes have gas water heating. The evaluation found that duct leakage, external wall insulation, and ceiling insulation have the lowest rate of compliance and the highest potential for energy savings if non-compliant homes were brought to code-minimum levels.