NGBS 2025: What Multifamily Builders Must Recalibrate Before the Next Permitting Cycle

The 2025 revision of ICC 700 reshapes how green certification interacts with energy code, durability, and indoor air quality.

The Problem: Where NGBS 2023 Left Builders Exposed

NAHB Research Center released the ICC 700-2025 National Green Building Standard in late 2024, and the deltas from the 2023 edition are concentrated in the categories that drive certification scoring for mid-rise multifamily: energy efficiency, indoor air quality, and building durability. Builders who locked their specifications around NGBS-2023 paths are finding that several previously accepted practices no longer carry the same points, and a few prescriptive paths have been tightened to align with ASHRAE 90.1-2022 baselines.

The issue is not that NGBS 2023 was wrong — it was simply calibrated to a different reference point. With the 2024 IECC now adopted in growing portions of the Midwest, and with ENERGY STAR Multifamily New Construction v3.2 establishing a stricter thermal envelope baseline, NGBS 2025 had to move in step. Projects that pursue NGBS Green Certified under the 2025 standard without verifying air leakage, duct leakage, and HVAC performance against the new performance paths will lose certification points they expected to bank.

The most common error HECS finds on multifamily projects is treating air sealing and duct leakage as a single trade activity. They are separate verification events under NGBS 2025, with distinct thresholds, and conflating them during pre-drywall inspection is the fastest way to fail a verifier walkthrough.

The Code: ICC 700-2025 and Its Companion Standards

ICC 700-2025 retains the four-tier certification structure — Bronze, Silver, Gold, and Emerald — but rebases the energy efficiency chapter against ASHRAE 90.1-2022 rather than the 2016 reference used in NGBS-2023. The practical effect is that builders running performance paths under ENERGY STAR MFNC v3.2 or the 2024 IECC are now closer to NGBS Gold compliance than they were two years ago, but the verification documentation is more demanding.

Key changes worth flagging:

• Chapter 7 (Energy Efficiency): New mandatory requirements for duct leakage testing in multifamily buildings, aligning with RESNET standards for total duct leakage and leakage to outside. Builders can no longer rely on visual inspection at rough-in.
• Chapter 9 (Indoor Environmental Quality): ASHRAE 62.2-2022 is now the explicit reference for whole-building ventilation rates in low-rise multifamily. The per-bedroom + per-square-foot calculation has not changed materially, but local exhaust runtime requirements have been clarified for kitchen and bath fans.
• Chapter 10 (Building Durability): Water management provisions tightened to require either a third-party verified water management plan or compliance with FORTIFIED Home 2025 durability elements for the highest tiers.
• Chapter 11 (Construction Practices): New requirements for material documentation chains — chain-of-custody for certified wood products and recycled content claims must now be retained for verifier audit.

The EPA radon map remains the reference for radon-resistant construction requirements under Chapter 9. Kentucky and Indiana sit in Zone 1 or Zone 2 depending on county, and HECS verifies passive radon systems where required by local jurisdiction overlay.

The HECS Approach: Verification Early, Not at Substantial Completion

HECS recommends that multifamily builders schedule NGBS verification as a three-event process rather than a single end-of-project inspection. The first event should occur at pre-drywall, when the building envelope and duct system are accessible. The second event covers insulation and air barrier continuity after drywall. The third is the final performance verification, including blower door testing, duct leakage testing, and HVAC functional testing.

This staged approach matters because NGBS 2025 verification requires a verifier signature at each milestone — the verifier cannot retroactively confirm work that was concealed before inspection. HECS has seen projects lose Emerald certification because a pre-drywall photo log was missing a single zone damper, or because duct leakage results were not transmitted to the verifier before drywall closed the chase.

The third-party verifier role is distinct from the rater or energy modeler. Under NGBS Green Certified Verifier protocols, the verifier confirms that design documents, material certifications, and field performance data together satisfy the standard. HECS provides this verification function with an NCI Certified air balancer on staff, which means the same technician who performs the blower door and duct leakage tests can also document the HVAC balance results in the format the NGBS reviewer expects.

What HECS Verifies: Deliverables That Hold Up at Audit

The HECS verification package for an NGBS 2025 multifamily project includes:

• Pre-drywall inspection report — photo-logged verification of air barrier continuity, insulation grade, window flashing, and duct sealing before concealment.
• Blower door test results — building envelope airtightness reported as ACH50 and CFM50, with building volume calculations.
• Duct leakage test results — total leakage and leakage to outside per RESNET standards, with the specific test method (pressure pan vs. duct pressurization) documented.
• HVAC balance report — per ASHRAE 111 tolerances, with supply, return, and exhaust CFM measured and compared to design intent.
• Ventilation rate calculations — per ASHRAE 62.2-2022, including runtime assumptions for local exhaust fans.
• Radon system verification — passive or active system confirmation where Zone 1 or Zone 2 applies.

Common Pitfall: Performance Path Documentation

The performance path under NGBS 2025 lets builders trade prescriptive measures against an energy model, but the documentation must show that the as-built performance matches the modeled performance. HECS has reviewed projects where the energy model showed a 7% margin against the target, but actual blower door and duct leakage results pushed as-built performance below the modeled number. The certification reviewer flags this as a documentation failure, not a design failure — but the effect is the same: points are not awarded.

The mitigation is straightforward. Test before drywall closes. Run a preliminary blower door at pre-drywall to confirm envelope airtightness is on track. If numbers are high, seal and retest. By the time drywall is up, remediation costs roughly five to eight times what pre-drywall sealing would have cost.

Frequently Asked Questions

Does NGBS 2025 require duct leakage testing for every multifamily unit? Yes. Chapter 7 now requires tested duct leakage per RESNET standards for in-unit HVAC systems, not just a visual inspection at rough-in. Builders can sample per the standard's testing protocol, but every sampled unit must meet the leakage-to-outside threshold.

Can a project pursue both NGBS 2025 Green Certification and FORTIFIED Home 2025? Yes, and there is overlap in the durability chapters that can reduce duplicate documentation. HECS coordinates the verifier functions so a single set of field photos can satisfy both programs where the standards align.

How does NGBS 2025 interact with ENERGY STAR MFNC v3.2? ENERGY STAR MFNC v3.2 remains an acceptable compliance path for NGBS Chapter 7 energy points, but the verifier must document the ENERGY STAR certificate and the supporting test results separately. HECS pulls both into a single verification packet.

How to Engage HECS

HECS provides NGBS Green Certified Verifier services across Kentucky, Indiana, Ohio, Tennessee, Illinois, and Missouri, with on-site scheduling typically within two to three weeks of contract. The relevant HECS services for multifamily NGBS 2025 projects include blower door testing, duct leakage testing, HVAC testing and balancing, and radon testing. To scope a project, call (859) 983-7382 or email [email protected]. Project intake and scheduling are handled through hecsusa.com/contact/, and the full service catalog is available at hecsusa.com/services/.