ANSI/RESNET/ICC 301 addenda through 2025 and the June 30, 2026 §45L deadline converge on multifamily rating documentation.
Multifamily builders chasing IRC §45L credits before the 2026-06-30 acquisition deadline are running into a documentation problem the old playbook did not anticipate. The HERS Index threshold has not moved, but the supporting evidence required by ANSI/RESNET/ICC 301-2022 plus addenda through 2025 has tightened on three fronts: sampling rules, registry discipline, and reference-home assumptions. HECS is seeing credit claims delayed or denied because the rating file does not reconcile with the IECC certificate on the same unit.
The structural issue is simple. A HERS rater files under one set of rules; the code official inspects under another; the tax credit package is assembled by a third party who never sees either file. By 2026, the gap between those three artifacts is the most common reason a §45L claim gets audited. For projects in Kentucky, Indiana, and Ohio — most of which sit in CZ 4A with northeastern counties in CZ 5A per the DOE Building America climate map — the binding air-leakage limit under 2024 IECC Table R402.4.1.1 is 3.0 ACH50, not 5.0. That number flows directly into the HERS reference home.
Working with HECS. HECS assembles the HERS rating, code compliance testing, and §45L documentation package from a single set of field data for projects in Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri. For a scope call: (859) 983-7382 or hecsusa.com/contact/.
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Call (859) 983-7382 Get a QuoteThe current revision is ANSI/RESNET/ICC 301-2022 plus addenda through 2025. Most changes are addenda, not full revisions. HECS reads the addenda as three operational shifts on multifamily projects.
First, sampling under ANSI/RESNET/ICC 380 (the sampling protocol referenced by 2024 IECC R405 and Table R405.4.2(1)) is no longer treated as a builder's option. Sample sizes are dictated by building height and unit count, and a failed sample triggers re-testing on adjacent units, not on the failed unit alone. Second, every rating must be registered with an ANSI-accredited HERS Provider, and the registry submission now has to reconcile with the ENERGY STAR or NGBS submission on the same property — HECS has rejected project files where the HERS Provider registry date post-dated the certificate of occupancy. Third, the reference-home assumptions now align more strictly with ASHRAE 90.1 versions specified by the program under which the building is being certified, rather than letting the rater pick the most favorable baseline.
For ENERGY STAR MFNC v1.3 (Rev05) national projects, common areas must meet ASHRAE 90.1-2019 and the ERI target is keyed to that reference home. The HVAC Functional Testing Checklist is required for participating units. For NGBS-2023 certifications, third-party verification is required at every tier, and verifier credentials are tier-dependent and pathway-dependent — a statement that "NGBS requires a HERS Rater for blower door" is overstated unless the chosen compliance pathway actually invokes RESNET.
A §45L package is only as strong as the field data behind it. HECS builds the file around five verified artifacts, each of which appears as its own deliverable. For a Louisville or Lexington garden-style project, the package typically includes: a registered HERS rating from the ANSI-accredited provider, a blower door test report tied to 2024 IECC R402.4.1.2 and ASTM E779, a duct leakage to outside test per 2024 IECC R403.3.5, a ventilation rate calculation per ASHRAE 62.2-2022 §4.1 with local exhaust documented per §4.3, and a combustion safety check on any gas appliances per NCI Combustion Performance & Carbon Monoxide Safety.
| Field Test | Code Anchor | HECS Threshold Practice |
|---|---|---|
| Blower door (ACH50) | 2024 IECC R402.4.1.2 | ≤ 3.0 ACH50 in CZ 3-8, including all KY/IN projects |
| Duct leakage to outside | 2024 IECC R403.3.5 | ≤ 4 CFM25 per 100 ft² conditioned area |
| Duct leakage (ENERGY STAR MFNC) | MFNC v1.3 Rev05 | ≤ 6 CFM25 rough-in / ≤ 8 CFM25 post-construction |
| Whole-building ventilation | ASHRAE 62.2-2022 §4.1 | Q_total = 0.03·A_floor + 7.5·(N_br+1) cfm |
| Local exhaust | ASHRAE 62.2-2022 §4.3 | Kitchen ≥100 cfm intermittent; bath ≥50 cfm intermittent |
Two pitfalls HECS flags routinely. First, a unit that meets 3.0 ACH50 at rough-in can drift to 4-5 ACH50 at final if the air barrier is not inspected — 2024 IECC R402.4.1.1 requires visible air-barrier inspection, and many jurisdictions will not accept the final test without it. Second, the duct tightness sample on a multifamily building under ANSI/RESNET/ICC 380 has to be drawn from units whose duct runs are representative of the worst case — typically top-floor units with the longest trunk runs — not the easiest-to-pass units.
The §45L credit value sits at $2,500 base plus a $1,000 prevailing-wage bonus under the post-OBBB formula, with homes acquired after 2026-06-30 ineligible. Acquisition is sale closing, not certificate of occupancy — HECS builders who push CO into July routinely lose the credit on units that would have qualified.
Does RESNET 301-2022 require a full new HERS rating for projects permitted before 2025 addenda were published? No. Addenda apply prospectively based on the rating's registration date with the ANSI-accredited HERS Provider. HECS confirms the applicable addendum set in the project file before the rater is dispatched.
Can a multifamily builder use sampling to claim §45L on every unit in the building? Sampling under ANSI/RESNET/ICC 380 and 2024 IECC Table R405.4.2(1) covers the energy rating, but the §45L acquisition file still requires per-unit documentation of sale closing date and certification status. HECS produces a per-unit acquisition schedule alongside the sampled rating file.
What is the most common documentation gap that costs a §45L claim? Reconciliation between the HERS Provider registry date and the certificate of occupancy date on the same unit. HECS ties both dates into a single audit trail before the §45L package is signed, because IRS review under §45L routinely asks for that reconciliation first.
HECS handles 45L tax credit documentation, HERS ratings, blower door testing, duct leakage testing, HVAC testing and balancing, and ENERGY STAR MFNC verification for projects in Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri. The relevant HECS service page for this topic is hecsusa.com/services/, and intake runs through hecsusa.com/contact/ or (859) 983-7382 / [email protected]. HECS also serves Louisville KY, Lexington KY, Cincinnati OH, and Indianapolis IN directly, with Nashville TN, Evansville IN, Columbus OH, and St. Louis MO covered on a scheduled route. Engage HECS early — at design development if possible — so the rater, code tester, and §45L package are sequenced against the same acquisition calendar.
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