§45L Tax Credit: 2024 IECC & ENERGY STAR Paths for Kentucky Builders

Code-required verification, not optional certification, by June 30, 2026.

Why §45L Matters for Developers in Kentucky and the Surrounding Region

The federal energy-efficient home improvement credit under 26 U.S.C. §45L delivers up to $5,000 per qualifying unit for developers and contractors building ENERGY STAR certified homes. The current §45L statutory window, as amended most recently by the Inflation Reduction Act of 2022, runs through December 31, 2032. However, the IRS qualification pathway requires builders to meet specific energy-saving thresholds against an established baseline code — typically the 2006 IECC for dwelling units constructed before January 1, 2026, per §45L(e) amendments.

HECS observes consistent confusion across Kentucky and southern Indiana projects: builders assume ENERGY STAR Multifamily certification alone satisfies §45L, then learn at tax filing that the dwelling must also demonstrate the required percentage of energy savings relative to the baseline. Both conditions must be met independently.

For builders in Louisville, Lexington, and Cincinnati metros, the practical deadline pressure is documentation — not construction. Construction must be substantially complete and the certification issued before the unit is sold or leased. The June 30, 2026 date that dominates builder conversation refers to the ENERGY STAR v3.1 program sunset for new certifications; v3.2 takes effect afterward with tightened thresholds.

Verification Pathways: Three Routes Under §45L

§45L permits three certification routes for dwelling units (acquisition or construction placed in service after December 31, 2021 and before January 1, 2027 per the extension in Public Law 117-169). Each requires different documentation, and selecting the wrong path is a common pitfall on multifamily projects.

Route 1 — 2006 IECC baseline plus 50% energy savings: Requires HERS index verification demonstrating the certified home achieves 50% or greater annual energy cost savings compared to a reference home built to the 2006 IECC. HECS confirms the baseline through RESNET HERS Index documentation.

Route 2 — 2006 IECC baseline plus ENERGY STAR certification: The home meets the 2006 IECC baseline (verified through HERS) and is certified under ENERGY STAR Residential New Construction programs. This is the most commonly used path for production builders.

Route 3 — 2021 IECC compliance plus ENERGY STAR: For dwelling units placed in service after December 31, 2022, builders may alternatively demonstrate compliance with the 2021 IECC plus ENERGY STAR certification. This route provides a cleaner threshold for projects already targeting 2021 IECC.

The relevant §45L subsections for the energy-savings thresholds and baseline definitions are §45L(a)(2) (eligible property) and §45L(e)(2) (energy-savings percentage). HECS recommends tax counsel review specific subsection application per project.

Working with HECS

HECS handles ENERGY STAR Multifamily Reviewer services and 45L Tax Credit Certification across Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri. For a scope call: (859) 983-7382 or hecsusa.com/contact/.

2024 IECC Air Leakage Requirements Affecting §45L Documentation

The 2024 IECC residential provisions under R402.4.1 establish air leakage thresholds for dwellings in Climate Zone 4A. The testing requirements are specified separately under R402.4.1.2, which references the mandatory blower door test methodology.

For Climate Zone 4A dwellings subject to the 2024 IECC, the air leakage rate must not exceed a defined CFM per square foot of conditioned floor area value as specified in Table R402.4.1.1. Duct leakage to outside is tested per R403.3.5, with total duct leakage not exceeding values specified in the same table for CZ 4A.

HECS notes that builders targeting §45L and ENERGY STAR simultaneously should schedule blower door and duct leakage testing simultaneously with HERS modeling to avoid duplicated site visits. The blower door test must be conducted after construction is substantially complete and all penetrations sealed.

Common Pitfalls on §45L Submissions

Three issues account for the majority of failed §45L claims on HECS projects:

1. Baseline selection error — Builders in Kentucky and southern Indiana frequently select the 2021 IECC baseline for projects that should reference the 2006 IECC. The applicable baseline depends on placed-in-service date, not construction start date. §45L(e)(1) governs baseline code selection.

1. Certification timing — ENERGY STAR certification must be issued before the dwelling is sold or leased. HECS has observed multifamily projects where units were leased before certification was finalized, disqualifying the credit claim.

1. Missing third-party verification — Self-certification by builders does not satisfy ENERGY STAR or RESNET requirements. Both require a certified verifier (HECS holds ENERGY STAR Multifamily Reviewer and RESNET HERS Rater certifications).

Additional issues include incorrect HERS Index software version (RESNET requires current ANSI 301-compliant tools), incomplete duct leakage test reports, and failure to maintain documentation for at least three years post-claim per IRS guidance.

Frequently Asked Questions

Does §45L require a third-party energy rater or can builders self-certify?

§45L requires certification by an accredited provider under RESNET standards. Self-certification by the builder does not satisfy the statutory threshold. HECS holds RESNET Certified HERS Rater and ENERGY STAR Multifamily Reviewer credentials, enabling combined documentation on a single site visit.

What is the difference between ENERGY STAR v3.1 and v3.2 for §45L projects?

Both program versions qualify under §45L if the certification is issued before the program sunset date for v3.1 (June 30, 2026 for new certifications). v3.2 introduces revised infiltration and duct leakage requirements. Projects certified under v3.1 prior to the sunset remain valid for §45L purposes through their placed-in-service date.

How does blower door testing integrate with §45L documentation?

Blower door testing provides the building air leakage rate input for the HERS Index calculation, which determines whether the dwelling achieves the energy-savings percentage required by §45L. HECS conducts blower door testing per ANSI/RESNET/ICC 380 and integrates results directly into the HERS model for RESNET certification.

How to Engage HECS

HECS provides ENERGY STAR Multifamily Reviewer services, 45L Tax Credit Certification, blower door testing, and duct leakage testing for projects across Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri. The firm coordinates HERS modeling, ENERGY STAR documentation, and §45L compliance verification as an integrated scope to reduce field visits and documentation gaps. Builders and developers in Louisville KY, Lexington KY, Cincinnati OH, Indianapolis IN, Nashville TN, St. Louis MO, Chicago IL, Evansville IN, and Columbus OH can initiate a scope review by calling (859) 983-7382 or emailing hecs@hecsusa.com. Service details are at hecsusa.com/services/, and project-specific scopes can be requested at hecsusa.com/contact/. For builders targeting §45L before the v3.1 sunset, the relevant HECS service page is hecsusa.com/45l-tax-credit-louisville-ky/.