Illinois Building Energy Codes

Code Level

Base Code

Authority

Authorized by – Statute. 2009's Energy Efficient Building Act modified the previous Energy Efficient Commercial Building Act to require the latest version of the IECC as the building energy code for both commercial and residential buildings. The statute is found at 20 ILCS 3125. Administrative rules for the Illinois Energy Conservation Code are found at 71 IAC 600.

Oversight – The building codes, including the base and stretch energy code, are overseen by the Capital Development Board (CDB), and more specifically by the CDB's Division of Building Codes & Regulations. The Illinois Energy Code Advisory Council meets regularly to evaluate energy code issues and provide advice to the board.

Code Change Process – Regulatory and Legislative.  The Illinois Energy Code Advisory Council (ILECAC) begins the process of reviewing the most recent code version and accepting public comments. Once approved by the ILECAC, code language is sent to the CDB for further review and public comment, If changes are proposed during the CDB review, the code language can be sent back to the ILECAC for their review and edits. Finally, once finalized, the CDB sends the code to the Illinois General Assembly's Joint Committee on Administrative Rules (JCAR) for final review and approval.

Code Change Cycle - Every 3 years, concurrent with updates to the model energy code.

Compliance

Enforcement - The Capital Development Board, along with the Department of Commerce and Economic Opportunity are responsible for defining compliance procedures. Code enforcement is the duty of the local jurisdiction, who must meet minimum compliance documentation requirements.

Implementation/Compliance Studies – The Illinois Department of Commerce and Economic Opportunity conducted a residential and commercial building energy code baseline compliance study in 2014. Click here for a full report.

As of 1/1/2025, authorized by Public Act 103-0510, Illinois municipalities must report their adopted building codes to the Capital Development Board. This information is made public through the Illinois Municipal Code Directory.

Stretch Code

A stretch code is an alternative energy code that goes above the minimum base energy code requirements. Once formally adopted by a municipality, the stretch code takes the place of the state base energy code and establishes the minimum energy efficiency requirements for new construction, additions and major renovations.

Authority

Authorized by - Statute. The Energy Efficient Building Act mandates the creation of an Illinois stretch energy code, to be updated every three years to meet established targets. This requirement was passed in the 2021 Climate and Equitable Jobs Act (CEJA), directing the Illinois Capital Development Board (CDB) to create a residential and commercial stretch energy code that can be adopted by individual municipalities. According to this legislation, the stretch code must meet a set of specific site energy index performance targets that become increasingly stringent over time, with a new target approximately every three years.

State funded facilities are required to comply with the Illinois Commercial Stretch Energy Code.

Commercial Building Requirements

DeadlineSite Energy Index Maximum* Efficiency as compared to the 2006 IECC
6/30/240.60At least 40% more efficient
12/31/260.50 At least 50% more efficient
12/31/290.44 At least 56% more efficient
12/31/320.39 At least 61% more efficient

Residential Building Requirements

DeadlineSite Energy Index Maximum* Efficiency as compared to the 2006 IECC
6/30/240.50 At least 50% more efficient
12/31/260.40 At least 60% more efficient
12/31/290.33 At least 67% more efficient
12/31/320.25 At least 75% more efficient

* Site Energy Index Maximum denotes the required efficiency level of the stretch code as compared to the 2006 IECC. For example, a site energy index maximum of .25 means the new code must be at least 75% more efficient than the 2006 IECC. Efficiency is based on conservation measures alone and does not include credits for on or off-site energy production.

Oversight – The building codes, including the base and stretch energy code, are overseen by the Capital Development Board (CDB), and more specifically by the CDB's Division of Building Codes & Regulations. The Illinois Energy Code Advisory Council (ILECAC) meets regularly to evaluate energy code issues and provide advice to the board.

Code Change Process – Regulatory and Legislative. The Illinois Energy Code Advisory Council begins the process of developing the standards of the stretch code to meet CEJA site energy index targets. At this point in the process, public comments are accepted and considered. Once approved by the ILECAC, code language is sent to the CDB for further review and public comment. If changes are proposed during the review by the CDB, the code language can be sent back to the ILECAC for their review and edits. Finally, once finalized, the CDB sends the code to the General Assembly’s Joint Committee on Administrative Rules (JCAR) for final review and approval.

Code Change Cycle - Every 3 years, in line with Energy Efficient Building Act requirements. In 2025, HB3510 amended the previous code change cycle to alternate the year of development for the base and stretch codes. Deadlines listed on this page reflect the updated timeline.

Primary Contacts