Fort Collins Adopts Stricter 2024 Energy Code
The 2024 IECC is now in effect in Fort Collins, and local amendments push requirements further than the base code in nearly every category.
Published June 5, 2026
Effective December 26, 2025, the City of Fort Collins replaced the 2021 International Energy Conservation Code with the 2024 IECC, but with local amendments that go further than the base code in nearly every area. Builders, designers, and mechanical contractors working in Fort Collins should understand that this is not a routine code update. The ordinance introduces new mandatory requirements with no equivalent in the base 2024 IECC but are in alignment with the Colorado Model Low Energy and Carbon Code, including electric-readiness infrastructure for every combustion appliance, demand-responsive controls for heating, cooling, and water-heating systems, and a stepped trajectory toward zero-carbon construction that spans the 2030 code cycle.
Tighter Envelope and Air Sealing Standards.
The Fort Collins amendments tighten the thermal envelope beyond base code minimums for Climate Zone 5. Various trade off paths still exist in the amendments but with tighter restrictions such as a compactness ratio factor for hot water distribution. Commercial whole-building air leakage is limited to 0.25 cfm/ft² at 75 Pa, a 30% reduction from the base code's 0.35 limit, and third-party blower door testing is mandatory for all new construction. Residential testing follows a Fort Collins-specific protocol, and multifamily buildings face unit-by-unit sampling requirements with correction-and-retest requirements for failures. All insulation, in both residential and commercial projects, is now clearly specified to be installed to Grade 1 standards per ANSI/RESNET/ICC 301; a clarification of the standard in the base code.
Electric Ready, Solar Ready, and the Path to Zero Carbon.
Among the most consequential local additions are the Electric Ready provisions in Sections R409 and C410. Every new building with combustion equipment, including gas furnaces, boilers, water heaters, and cooking appliances, must be wired at the time of construction with a dedicated circuit, adjacent junction box or receptacle, reserved panel space, and physical space for future all-electric replacements. Space-heating circuits must be sized using a conversion factor tied to Fort Collins's 6°F design temperature. Solar-ready zones are mandatory for new residential and commercial buildings, with specific area, orientation, obstruction, and conduit-pathway requirements. Looking further ahead, both Appendix RZ (residential) and Appendix CZ (commercial) establish code-cycle targets running through 2030: residential buildings must achieve an Energy Rating Index of 50 or lower and a CO2e Index of 50 or lower today, stepping to zero CO2e by the 2030 code. Commercial buildings face gross site EUI targets by building type and annual emission rates for the Rocky Mountain region. Fort Collins has effectively used this code adoption to set a clear direction: each code cycle upgrade will result in buildings operating at zero carbon by 2030.
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