Illinois closed out 2025 with significant strides in energy efficiency. By simultaneously updating statewide regulations and breaking ground on innovative residential projects, the state is demonstrating how policy and construction practices work together to create a more efficient community.
New Energy Code, Who This?
As of November 30, 2025, Illinois has officially adopted the 2024 International Energy Conservation Code (IECC). This adoption establishes a new floor for energy efficiency in buildings across all new construction and major renovations in the state.
Analysis shows that the new code produces meaningful life-cycle savings for homeowners, with a $3,790 and $2,496 savings per home for both of Illinois' climate zones, 4 and 5, respectively. In addition, the simple payback period for these efficiency improvements is immediate compared to the 2021 IECC. Beyond cost savings, the code includes updated definitions and flexible compliance paths designed to make implementation easier for builders.
Looking Ahead: The 2026 Stretch Code
For communities looking to go beyond the base code, you are in luck. The Capital Development Board (CDB) is currently finalizing the 2026 Illinois Stretch Energy Code and has now published the draft to its website.
Mandated by the Climate and Equitable Jobs Act (CEJA), this voluntary code allows municipalities to adopt more aggressive performance targets. The stretch code is designed to accelerate market transformation by emphasizing envelope upgrades and system efficiency, providing a consistent "off-the-shelf" option for municipalities that want to lead on sustainability without drafting their own unique ordinances.
The 2023 Stretch Energy Code is currently available to municipalities to adopt with Evanston becoming the first municipality in the state to adopt the improved energy code in 2025. The updated 2026 Stretch Energy Code improves on the 2023 version by increasing energy efficiency credits and requirements while ensuring it meets the required efficiency measures established in the Climate and Equitable Jobs Act (CEJA).
The 2026 Stretch Energy Code is currently in its final stages of development and is slated for a tentative adoptable date of the third quarter of 2026.
A Promising 2026
The timing between the new 2024 IECC and the 2026 Stretch Code highlights a continued push forward for the Midwest's energy landscape. Whether through the mandatory state code or voluntary stretch codes, the goal remains consistent: to deliver practical, measurable, and affordable energy solutions to Illinois residents. With the 2024 IECC now automatically in effect statewide and an updated Illinois Stretch Energy Code becoming available to adopt mid- to late- 2026, Illinois is building a clear path toward a resilient, healthier future.