Builder-side documentation, sampling protocols, and the numbers code officials enforce.

The Gap Between Permitted Plans and What the Inspector Accepts

Most failures we encounter on Kentucky multifamily projects are not design failures. They are evidence failures. The mechanical designer hit 2024 IECC R402.4.1.2 on paper, the framer sealed the top plates, and the HVAC sub sealed the boots. Yet the verifier shows up with a blower door and the building fails. Three things drive this outcome on our projects: incorrect ACH50 mapping, missing third-party verification, and duct leakage tested outside the code-allowed protocol.

Kentucky sits in climate zones 4A and 5A, never 3 or warmer. Per the 2024 IECC Climate Zone Map (DOE Building America), the binding blower-door limit for any Kentucky county is the Table R402.4.1.1 cap for CZ 3-8 — not the looser cap for CZ 0-2. In our experience the reverse is still being installed on plan sets. The 2018 mapping (5 ACH50 in CZ 4, 3 in CZ 5) is wrong under the 2024 code cycle, and it keeps showing up in stale compliance notes.

A second failure mode is documentation. Code officials in Kentucky will accept sampling under Table R405.4.2(1) for multifamily, but only when the sample size, unit selection, and failure protocol match the table. Builders who show up with a single blower-door test from the model unit — and call that the building result — get rejected.

Where code officials consistently push back

• Blower door results not run per ASTM E779 or equivalent.
• Duct leakage tested at rough-in only, with no post-construction confirmation.
• Visible air-barrier inspection missing from the project record.
• ACH50 target pulled from a 2018 IECC cheat sheet instead of the 2024 cycle.
• No third-party verification when the program requires one.

What the 2024 IECC and ENERGY STAR MFNC v1.3 (Rev05) Actually Require

The relevant residential air-sealing and duct-tightness provisions live in a handful of sections, and they each have a specific test method behind them:

ENERGY STAR MFNC v1.3 (Rev05) is the current national revision (January 2025). The HVAC Functional Testing Checklist is required for participating units, and the duct leakage thresholds are looser than IECC — which means a building can fail IECC while passing MFNC, or vice versa. Builders chasing both programs cannot average the numbers; they have to hit the tighter one.

If the project is also pursuing NGBS-2023 certification, every tier — Bronze through Emerald — requires third-party verification under §702.1.1, and the air-leakage and duct-leakage requirements in Chapter 7 layer on top of IECC. Verifier credentials are tier-dependent and pathway-dependent; specific compliance pathways may require RESNET HERS credentials even when an NGBS verifier is on the project.

Working with HECS

HECS handles blower door testing, duct leakage testing, and ENERGY STAR / NGBS verification for multifamily projects across Kentucky, North Carolina, Alabama, Georgia, West Virginia, Kansas, and Missouri. Our NCI-certified testers run residential airflow measurements against the code-required tolerances and produce the third-party documentation code officials accept. For a scope call: (859) 983-7382 or [email protected].

The Sampling Question: One Test, Five Tests, or Twenty

Multifamily builders consistently underestimate the sampling problem. Under ANSI/RESNET/ICC 301-2022, multi-family projects may use sampling protocols per RESNET/ICC 380, with sample sizes tied to building height and unit count. IECC Table R405.4.2(1) governs the simulated-performance path; the prescriptive path through R402.4.1.2 is unit-by-unit.

Three practical rules from our project work:

• If you are running the ERI path under R405, sample size follows RESNET/ICC 380, not a code official's preference.
• If any unit in the sample fails the ACH50 or duct leakage cap, the failure protocol determines whether additional units are tested — not whether the building passes.
• A passing model unit does not certify the building. Code officials who see one model-unit result and no sampling protocol will reject the file.

The builder-side documentation that holds up under audit lists every tested unit by address, the test result, the equipment used (calibrated blower door, gauge model, last calibration date), the technician's certification, and a photo of the manometer at the time of test. HECS delivers that package as standard — it is what gets a project to CO without a re-test callback.

What Shows Up on a HECS Multifamily Verification Report

The deliverable is a single binder that closes out the air-sealing, duct-tightness, and ventilation sections of the code file. Contents vary by program mix, but the standard package includes:

• Project header with address, code cycle, climate zone, and program targets.
• Blower door results per tested unit, ACH50 value, equipment serial numbers, and calibration date.
• Duct leakage results in tonality per ASTM E1554 or RESNET/ICC Std. 380, rough-in and post-construction.
• Sampling protocol reference and per-unit selection rationale under Table R405.4.2(1) when applicable.
• Visible air-barrier inspection sign-off under R402.4.1.1.
• For ENERGY STAR projects, the HVAC Functional Testing Checklist per MFNC v1.3 (Rev05).
• For NGBS projects, verifier credentials under NGBS-2023 §702.1.1.

Where this typically fails in our experience: the report is run late, after drywall is closed and the electrician has changed the panel. HECS schedules the rough-in duct test before insulation, the post-construction duct test after trim-out, and the blower door before the final code inspection. Reverse that order and the failed unit cannot be re-sealed without demo.

Frequently Asked Questions

Does a passing model unit satisfy 2024 IECC blower-door requirements for a Kentucky multifamily building? No. Under R402.4.1.2, the building must be tested. Multifamily projects on the simulated-performance path may use sampling per R405 and Table R405.4.2(1); the prescriptive path requires unit-by-unit testing. HECS runs the sampling protocol and delivers per-unit results code officials accept.

What is the binding ACH50 cap for a Louisville or Lexington project? Three ACH50, per the 2024 IECC Climate Zone Map and Table R402.4.1.1. Kentucky sits in CZ 4A and 5A, both inside the CZ 3-8 grouping. The older 5.0 cap does not apply. HECS verifies the climate-zone designation as part of every blower door report.

Can a project meet ENERGY STAR MFNC and still fail 2024 IECC duct leakage? Yes. [MFNC v1.3 (Rev05)](