Addenda-level changes to ANSI/RESNET/ICC 301, and what to capture in your 45L file before June 30, 2026.
The 45L credit collapses for homes acquired after June 30, 2026. Public Law 119-21 (the One Big Beautiful Bill, signed July 4, 2025) accelerated the §45L sunset from 2032 to mid-2026 — a fact that is still not on every developer's calendar. The HERS Index pathway under ANSI/RESNET/ICC 301-2022 is the most flexible way to qualify on the energy side, but the 2025 addenda have tightened the documentation that RESNET-accredited Providers will accept on a 45L file. Builders who relied on 2022-era sampling tables or older ERI reference home assumptions are finding their rater's registry submission kicked back. The result: lost weeks, missed closing windows, and an avoidable gap between "certified" and "fundable."
The deeper issue is that three code families now have to agree on the same set of numbers — the 2024 IECC blower door table, the ANSI 301 ERI reference, and the ENERGY STAR MFNC v1.3 (Rev05) thermal envelope checklist. When those documents disagree on a threshold, the rater has to default to the most conservative reading. HECS sees that friction most often on projects where the developer thinks they qualified under one program but the 45L file shows a different ACH50 or duct leakage number.
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Call (859) 983-7382 Get a QuoteANSI/RESNET/ICC 301-2022 with addenda through 2025 is the current revision. The 2026 cycle is not a full re-issue — it is addenda layered on the 2022 base, which is the most common source of confusion. Concrete shifts that affect 45L files:
For envelope targets, the 2024 IECC Table R402.4.1.1 mapping is the binding reference for any 45L project: Climate Zones 0-2 cap at 5.0 ACH50, Zones 3-8 cap at 3.0 ACH50. HECS projects in Kentucky and Indiana are exclusively CZ 4A or CZ 5A, so the 3.0 ACH50 limit is the working number — not 5.0. Louisville (Jefferson Co.) sits in 4A.
HECS runs the rating side as a parallel track to the certification side, not a sequential one. The rater and the HERS Provider registry entries are drafted at rough-in, not at certificate of occupancy. That sequencing lets the team catch a duct leakage failure (2024 IECC R402.4.2 / R403.3.5 — verified total leakage to outside ≤ 4 CFM25 per 100 ft² conditioned floor area) before drywall closes the system.
HECS handles 45L Tax Credit Certification for multifamily projects across Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri. For a scope call on a 45L file with a 2026-06-30 closing deadline: (859) 983-7382 or hecsusa.com/contact/. Our full 45L scope is outlined at hecsusa.com/45l-tax-credit-louisville-ky/.
The 45L package is a stack of three documents, and HECS treats each as a separate reviewable artifact rather than a single form. The blow-by-blow:
A common pitfall: relying on the ENERGY STAR MFNC thermal envelope checklist as the 45L evidence. The two programs share a HERS math basis but have different required test artifacts. HECS cross-checks the MFNC checklist against the 45L file before submittal to avoid the classic "passed MFNC, failed 45L" outcome.
Does the 45L credit require ENERGY STAR certification, or is HERS-only sufficient?
HERS-only is sufficient under §45L when the ERI target is met on the ASHRAE 90.1-2019 reference home and the rater is RESNET-certified and registered with an ANSI-accredited HERS Provider. ENERGY STAR MFNC v1.3 (Rev05) is a separate certification track that satisfies 45L via the certified-home pathway, but it is not required if the HERS-only path is documented cleanly.
What blower door threshold applies to a Louisville or Lexington multifamily project?
Both are CZ 4A under the 2024 IECC climate zone map, so the binding limit is 3.0 ACH50 per Table R402.4.1.1. Sampling is permitted per Table R405.4.2(1) for multi-family buildings. Projects in northeastern Kentucky counties (Boyd, Carter, Greenup, Lawrence, Elliott, Morgan, Rowan, Bath, Menifee, Montgomery, Robertson) are CZ 5A — same 3.0 ACH50 limit, but the heating-degree-day math on the ERI target shifts.
Can HECS handle both the HERS rating and the 45L certification submittal?
HECS handles the 45L certification documentation, the blower door test, the duct leakage test, and the cross-check against the ENERGY STAR MFNC v1.3 (Rev05) or NGBS-2023 envelope. The HERS Index calculation and Provider registry entry are performed by a RESNET Certified HERS Rater; HECS coordinates that workflow and assembles the 45L file so the rating, the test results, and the certification evidence line up cleanly before the 2026-06-30 closing date.
HECS supports 45L Tax Credit Certification, ENERGY STAR MFNC, NGBS Green, and EarthCraft documentation, along with the supporting blower door, duct leakage, and thermal imaging tests that anchor a 45L file. Geographic reach covers Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri, with active work in Louisville KY, Lexington KY, Cincinnati OH, Indianapolis IN, Nashville TN, and St. Louis MO. Start with a scope call at (859) 983-7382 or hecs@hecsusa.com, and review the full 45L scope at hecsusa.com/services/ and hecsusa.com/contact/. Locking the rating workflow before rough-in is the single highest-use move a developer can make on a 2026-closing 45L project.
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