The 2026 update is largely addenda-driven, and the 45L paperwork follows.
The One Big Beautiful Bill accelerated the §45L New Energy Efficient Home Credit sunset to June 30, 2026. Multifamily builders who waited until Q4 to assemble documentation are discovering that the underlying rating standard, ANSI/RESNET/ICC 301, has accumulated addenda through 2025 that change how HERS Index values are calculated and registered. A rating that was valid in 2023 may not satisfy an IRS reviewer looking for current-version compliance documentation.
HECS sees three recurring failure modes on multifamily 45L packages:
The binding code for envelope tightness in our service area is 2024 IECC R402.4.1.2 and Table R402.4.1.1: for climate zones 3 through 8 the verified blower door rate cannot exceed 3.0 ACH50. Kentucky and Indiana sit in CZ 4A and CZ 5A, so HECS treats 3.0 ACH50 as the working limit on every project, not 5.0.
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Call (859) 983-7382 Get a QuoteHECS registers and documents multifamily HERS ratings for 45L claims across Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri. Our rater coordinates with your HERS Provider, captures the sampling protocol, and packages the envelope and duct results in the format IRS reviewers expect. For a scope call: (859) 983-7382 or hecsusa.com/contact/.
ANSI/RESNET/ICC 301-2022 is the current published version; the 2025 addenda refine, rather than replace, the calculation methodology. The practical effect for multifamily builders is in three areas.
Reference home updates. The 2006 IECC reference home assumptions for HVAC distribution, hot water, and lighting have been adjusted. Projects rated before the addendum may show a HERS Index that no longer maps cleanly to the current ERI target used by ENERGY STAR MFNC v1.3 (Rev05). HECS flags any rating older than 12 months for re-check before submission.
Sampling. ANSI/RESNET/ICC 380 governs multi-family sampling for blower door, duct leakage, and ventilation ratings. Sample sizes scale with building height and unit count. 45L documentation must identify which units were tested, which were sampled, and what the per-unit index is. A single building-level ACH50 number, without the sampled-unit breakdown, is not enough.
Registry requirements. All HERS ratings must be registered with an ANSI-accredited HERS Provider. The Provider's registry record is what the IRS examiner pulls, not the rater's internal file. HECS confirms the registry ID, the rating date, and the software version (REM/Rate, Ekotrope, or approved equivalent) before the package leaves our office.
| Document | What IRS reviewer expects | HECS deliverable |
|---|---|---|
| HERS Index per unit | Current ERI target comparison, registry ID | Registered rating with Provider stamp |
| Blower door | Sampled units, ACH50 per R402.4.1.2 | Field log + sampling map |
| Duct leakage to outside | Total CFM25 per 100 ft² per R403.3.5 | Per-unit test report |
| Prevailing wage (bonus tier) | Payroll attestation | Coordination with GC |
On-site verification starts before insulation. HECS confirms penetration counts at the air barrier, then runs a blower door per ASTM E779 at the rough-in stage when possible, and again at final. For projects electing the Total UA alternative under 2024 IECC R402.1.2, HECS pulls the UA calculation from the design team and cross-checks the airtightness number against the alternative path.
Duct tightness verification follows 2024 IECC R403.3.5: verified total leakage to outside at or below 4 CFM25 per 100 ft² of conditioned floor area, tested per ASTM E1554 or ANSI/RESNET/ICC 380. For projects also pursuing NGBS-2023 certification, HECS aligns the duct test with §704.1 so the same report serves both programs.
Ventilation is documented against ASHRAE 62.2-2022 §4.1, with the whole-building ventilation rate meeting the equation Q_total = 0.03·A_floor + 7.5·(N_br+1) cfm. Local exhaust is verified per §4.3, kitchen ≥100 cfm intermittent or ≥25 cfm continuous, bathrooms ≥50 cfm intermittent. For projects in NFPA 54 jurisdictions, combustion safety is verified with calibrated analyzers at design firing rate.
The final deliverable is a 45L documentation binder that includes the registered HERS Index, sampling map, blower door and duct leakage logs, ventilation calculation, and prevailing-wage coordination notes. It is the same package HECS submits to an HERS Provider for NGBS or ENERGY STAR Multifamily when those programs are stacked on the same building.
Prevailing-wage bonus is the highest-value failure. The bonus tier requires certified payroll for every contractor and subcontractor on the qualifying unit. Builders who assume a HERS Index alone unlocks the full credit find out at audit that the bonus requires payroll attestation. HECS confirms with the GC which trades are in scope before the rating is finalized.
Rating currency is the second. A HERS Index registered against an older addendum version may not map to the 2025 ERI target that the IRS reviewer is comparing against. HECS re-issues ratings older than 12 months unless the addendum transition has been documented by the Provider.
Climate zone miscoding quietly pushes projects out of compliance. Most of Kentucky and Indiana sit in CZ 4A; northeastern counties of both states fall in CZ 5A. Both are bound by the 3.0 ACH50 limit under Table R402.4.1.1, there is no 5.0 ACH50 path for our geography. HECS verifies the climate zone from the county record before the first blower door test.
Does a HERS rating older than 12 months still qualify for §45L?
A registered HERS Index does not expire by date alone, but IRS reviewers expect the rating to reflect the current ANSI/RESNET/ICC 301 addenda. HECS flags any rating older than 12 months for re-check with the HERS Provider before submission.
Can multifamily builders use sampling for blower door and duct leakage on 45L projects?
Yes. ANSI/RESNET/ICC 380 governs sampling protocols for multi-family ratings; sample size scales with building height and unit count. HECS documents the sampled units and the per-unit index in the 45L binder.
What envelope tightness number does 45L actually require for Kentucky and Indiana?
§45L ties the credit to an ERI target, but the underlying airtightness is documented against the building code adopted at permit. In our service area that is 2024 IECC, so the binding blower door limit is 3.0 ACH50 under Table R402.4.1.1 for climate zones 4A and 5A.
HECS provides 45L documentation, HERS rating coordination, blower door and duct leakage testing, and NCI-certified air balancing for multifamily projects. We serve Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri, with active work in Louisville KY, Lexington KY, Cincinnati OH, Indianapolis IN, Nashville TN, and Evansville IN. Call (859) 983-7382 or email [email protected] to schedule a pre-construction scope review. Service details are at hecsusa.com/services/ and project intake is at hecsusa.com/contact/.
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