The New Colorado Model Low Energy and Carbon Code (MLECC) establishes rigorous performance benchmarks for building envelopes, focusing on high-performance insulation and enhanced air sealing to move homes toward net-zero energy readiness.

Insulation Standards

Insulation requirements vary by jurisdiction, with several major areas adopting the most stringent standards:

• Denver, Centennial, and Unincorporated Arapahoe County: These jurisdictions mandate R-49 attic insulation and R-20 wall insulation. To meet the R-20 wall requirement and minimize thermal bridging, these codes typically require the use of continuous insulation, such as polyiso.
• Colorado Springs: Currently maintains slightly lower thresholds, requiring R-38 attic insulation and R-19 wall insulation.

Air Sealing and Building Envelope Requirements

The MLECC introduces several measures to guarantee airtightness and thermal efficiency:

• Enhanced Air Sealing: The code requires advanced air sealing techniques designed to dramatically reduce thermal transfer.
• Duct Leakage Testing: Compliance involves mandatory testing of ductwork to ensure minimal energy loss through the HVAC system.
• High-Performance Windows: To support the building envelope, windows must meet strict thresholds by July 2026. In most jurisdictions (except Colorado Springs), this includes a U-value of 0.30 or lower and a Solar Heat Gain Coefficient (SHGC) of 0.25 or lower.
• Electric-Ready Provisions: New standards include requirements to make homes “electric-ready” to facilitate future electrification and carbon reduction goals.

• Model Low Energy and Carbon Code Mlecc Colorado: Essential Guide