RESNET 2026 HERS Changes: 45L Documentation for Multifamily Builders
TL;DR
- The 2026 addenda cycle shifts how ERI is calculated and sampled — and builders claiming the §45L credit need airtight file packets before the June 30, 2026 deadline.
- Specifically, the HERS Index hasn't been "rewritten" in 2026 — it has been incrementally revised through addenda to ANSI/RESNET/ICC 301-2022, the standard HECS uses on every multifamily rating.
- For example, nCI-certified testing and certification across KY, NC, AL, GA, WV, KS, MO.
Key facts
4 CFM25
6 CFM25
8 CFM25
3.0 ACH50
2.5 ACH50
2 CFM25
45L
ASHRAE 62.2.
Common questions this post answers
- What about What the 2026 HERS Update Actually Changes?
- Why This Matters for §45L Before the June 30, 2026 Deadline?
- What about Code Anchors HECS Verifies Against?
- What about What HECS Verifies and Delivers?
The 2026 addenda cycle shifts how ERI is calculated and sampled — and builders claiming the §45L credit need airtight file packets before the June 30, 2026 deadline.
What the 2026 HERS Update Actually Changes
The HERS Index hasn't been "rewritten" in 2026 — it has been incrementally revised through addenda to ANSI/RESNET/ICC 301-2022, the standard HECS uses on every multifamily rating. Addenda through 2025 adjust how reference home components, mechanical ventilation, and sampling are weighted in the Energy Rating Index (ERI). Builders and developers tracking "RESNET 2026" should treat the current revision as 301-2022 with active addenda, not a brand-new standard.
Three areas carry real consequences for documentation:
- Reference home weighting for heat pumps. Addenda adjust the efficiency baseline for cold-climate and variable-speed heat pumps in the reference home. Projects that previously cleared the 45L prevailing-wage threshold by a slim margin can drift in either direction depending on which addendum the rater's software implements.
- Ventilation interaction with ASHRAE 62.2. Updated ERI calculations reference ASHRAE 62.2-2022 whole-building and local-exhaust rates. Raters must confirm the ASHRAE 62.2 equation inputs (combined supply + exhaust meeting Q_total = 0.03·A_floor + 7.5·(N_br+1) cfm) match the software version in the registered file.
- Multi-family sampling protocol. ANSI/RESNET/ICC 380 governs sample size by building height and unit count, and 301 addenda refine how infiltration, duct leakage, and ERI interact inside a sampled unit. Builders cannot average ERI across unsampled units — each registered unit either passes on its own data or is documented within an approved sample.
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Call (859) 983-7382 Get a QuoteWhy This Matters for §45L Before the June 30, 2026 Deadline
The §45L credit expired for homes acquired after June 30, 2026 under Public Law 119-21 (the One Big Beautiful Bill Act, signed July 4, 2025), which accelerated the prior 2032 sunset. The §45L credit page confirms the 2026-06-30 cutoff for acquisitions. Anything closing on or before that date must have a registered HERS rating and a qualifying ERI before the lender or title company wires the credit.
Documentation problems HECS encounters on §45L files typically fall into three buckets:
- Stale software versions. The rater's rating was generated before the latest addendum, but the builder files the credit under a software build that has since been updated. IRS reviewers can request the rater's registered software build; mismatches invite disallowance.
- Missing sampling documentation. For multi-family projects, the file must include the 380 sample selection rationale and per-unit test records for the chosen units. Without the per-unit envelope and duct leakage data, the credit fails on documentation, not on ERI.
- Duct leakage assumed instead of tested. 2024 IECC R403.3.5 requires verified leakage to outside at or below 4 CFM25 per 100 ft² of conditioned floor area. ENERGY STAR MFNC v1.3 (Rev05) National — current revision per the EPA program page — applies 6 CFM25 rough-in / 8 CFM25 post-construction thresholds. Raters who skip the test and substitute default assumptions sink the credit.
Working with HECS
HECS handles FORTIFIED Roof evaluation certification for multifamily projects across Kentucky, North Carolina, Alabama, Georgia, West Virginia, Kansas, and Missouri. Each file includes a registered HERS rating, verified blower-door and duct-leakage data, and the sampling rationale your tax preparer needs at closing. For a scope call: (859) 983-7382 or hecsusa.com/contact/.
Code Anchors HECS Verifies Against
For Kentucky and Indiana projects, HECS confirms the climate zone, envelope, and duct tightness thresholds against the 2024 IECC and the DOE Building America climate zone map. Louisville and most of Kentucky sit in CZ 4A, with northeastern counties in CZ 5A; Indiana follows the same pattern. That means the binding air-leakage limit per Table R402.4.1.1 is 3.0 ACH50 — not 5.0 — because the 2024 IECC applies 3.0 across CZ 3-8.
| Threshold | Code reference | HECS project experience |
|---|---|---|
| Air leakage (CZ 4A/5A) | 2024 IECC R402.4.1.1, 3.0 ACH50 | Most multifamily projects test 1.5-2.5 ACH50 after balancing |
| Duct leakage to outside | 2024 IECC R403.3.5, 4 CFM25/100 ft² | Trunk-and-branch designs with mastic hit ≤2 CFM25/100 ft² |
| Ventilation rate | ASHRAE 62.2-2022 §4.1 | Per the 62.2 equation above; local exhaust per §4.3 |
| Multi-family sampling | ANSI/RESNET/ICC 380 | Sample size keyed to building height and unit count |
NGBS-2023 projects add another layer: ICC 700-2023 §702.1.1 requires third-party verification at every tier. NGBS Chapter 7 references the same air-leakage and duct-leakage thresholds as the 2024 IECC, and Chapter 9 §903 ties indoor environmental quality to ASHRAE 62.2-2022. Builders stacking NGBS on top of §45L cannot skip the verifier credential requirement at the Gold or Emerald tiers.
What HECS Verifies and Delivers
HECS packages each §45L file to withstand IRS documentation requests. The standard deliverable includes:
- Registered HERS rating through an ANSI-accredited HERS Provider, with the software build version stamped on the certificate.
- Blower door test results at rough-in and final for each sampled unit, recorded per ASTM E779 or equivalent per R402.4.1.2. For multi-family, sampling follows Table R405.4.2(1).
- Duct leakage to outside at rough-in and post-construction per R403.3.5, using a RESNET-certified duct leakage tester.
- Sampling rationale documenting the 380 protocol used, the units selected, and the field data for each.
- Prevailing-wage attestation support when the builder is claiming the enhanced credit amount.
A common pitfall HECS flags early: builders who lock in a contract price assuming the prevailing-wage bonus only to discover at the §45L documentation stage that the certification pathway was never selected. The ERI threshold for the base credit and the enhanced credit differ, and the rating file must reflect the correct pathway before closing.
Frequently Asked Questions
Does the 2026 RESNET update require re-rating projects already submitted for §45L? No. The relevant standard is ANSI/RESNET/ICC 301-2022 with addenda through 2025, and ratings generated under an active addendum remain valid for the qualifying unit. Builders should confirm the rater's software version matches the addenda in effect when the rating was generated.
Can a multifamily project use sampling for both the HERS rating and the §45L certification? Yes, when the project meets the ANSI/RESNET/ICC 380 sampling protocol and each sampled unit has a complete envelope, duct, and ventilation test record. The §45L file must include the sampling rationale and per-unit data, not a project average.
How does HECS document compliance with ASHRAE 62.2 inside a HERS rating file? The file references ASHRAE 62.2-2022 §4.1 and the whole-building ventilation equation, with measured local-exhaust rates per §4.3 captured in the rater's checklist. The ERI calculation assumes compliance, but HECS still verifies the field-installed ventilation rates on a sample basis.
How to Engage HECS
For §45L certification and HERS ratings on multifamily projects, HECS serves Kentucky, North Carolina, Alabama, Georgia, West Virginia, Kansas