Submittal Label Does Not Match the Assembled Storefront
A design-build team is replacing the storefront system on a four-story office building in Climate Zone 5. The specification requires NFRC-certified U-factor ≤0.34, SHGC ≤0.40, and a product labeled to the NAFS edition referenced by the adopted code. The submittal includes a label for a Series 450 fixed unit with U-factor 0.38, SHGC 0.36, and a certificate listing a 1-inch insulating glass unit with low-e coating on surface 2 and argon. The project actually proposes a 1-3/8-inch triple-glazed unit to improve acoustics. The contractor argues the label is close enough, notes SHGC passes, and proposes a COMcheck envelope trade-off. The owner’s representative must decide whether to approve the submittal, reject it, or request more information before glass is ordered.
1. Can the submitted NFRC label be used to demonstrate compliance with the specified U-factor? Explain.
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No. An NFRC label is not a generic certificate for a product family; it rates a defined frame, glazing make-up, spacer, gas fill, and operator configuration. The label covers a 1-inch IGU, while the proposed assembly is 1-3/8-inch triple glazing. The U-factor of 0.38 therefore cannot be transferred to the proposed unit. Even if the label matched, 0.38 is worse than the specified maximum of 0.34, so the prescriptive path fails on U-factor. The SHGC of 0.36 satisfies the 0.40 limit, but it does not cure the U-factor failure. The NAFS edition on the label must also be checked against the edition referenced by the adopted code; a label to an older edition may or may not be accepted by the code official.
2. What compliance paths remain if the exact assembly cannot meet the prescriptive U-factor?
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Three paths are worth evaluating. First, require a different product or glazing make-up with an NFRC-certified U-factor of 0.34 or better for the exact assembly. Second, use the code’s envelope trade-off or performance path, but only with a complete model that uses the actual U-factor and accounts for all envelope changes; a verbal “COMcheck trade-off” is not a compliance finding. Third, request a code official interpretation or variance only if the adopted code allows one. The team should not assume that improved SHGC or better acoustics can offset a U-factor miss outside an approved trade-off methodology.
3. What product-specific information should be verified before approving any alternate?
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Verify that the NFRC Certified Product Directory or CMA listing describes the exact frame, glazing make-up, spacer, gas, and operator being supplied. Confirm the certified U-factor, SHGC, visible transmittance, and condensation resistance ratings. Check the NAFS performance grade and design pressure, plus air, water, and structural ratings for the project’s wind load. Confirm the certification body, label validity, and whether the code official accepts the NAFS edition shown. Finally, compare the submittal’s thermal values with the specification and require a new label or listing whenever the assembly changes.