REPORTED R-VALUE vs. MODELED PERFORMANCE
2x6-depth walls: the label value vs. modeled performance once framing losses are counted
2x6-depth walls: the label value versus modeled performance once framing losses are counted. 2x6 closed-cell spray foam R-34 to R-20 effective. ThermaTech 5.5 inch panel R-21 to R-43 star, Intertek modeled performance equivalent versus wood framing, with a dashed R-21 conduction only marker. 2x6 open-cell spray foam R-20 to R-16 effective. 2x6 R-19 fiberglass batt R-19 to R-15 effective.
R-VALUE (h·ft²·°F/Btu)
REPORTED / NOMINAL R
ACTUAL MODELED
PERFORMANCE
APPLY HEAT LOSS THROUGH FRAMING
(THERMAL BRIDGING) + AIR LEAKAGE
R-43*
INTERTEK MODELED
PERFORMANCE EQUIVALENT
vs. wood framing
R-21 conduction only³
R-20 effective²
R-16 effective²
R-15 effective¹
Sources and notes
* Intertek report T6399.01-304-17R0 (06/02/26), Table 3: "Thermatech Insulation Nominal R-value" R-43 (2x4 center studs) / R-42 (2x6 center studs) vs. wood frame (R-50 / R-49 vs. steel frame). MODELED, not tested. It combines THERM conduction (effective R-21) with an ASSUMED 50% cut in infiltration heat loss (1.5 ACH vs. "typical" 6 ACH); panel air leakage "is assumed" and "has not been tested" (ASTM E2178/E2357). Intertek's combined "Total Effective R" is R-23.3, and the report doesn't show how it gets from R-23.3 to R-43. No air-leakage credit is applied to the spray-foam walls, which also air-seal.
¹ Same report, Table 3: ASHRAE 90.1-2022 App. A 2x6 wood-frame R-19 wall = effective R-15 (U-0.067). This is Intertek's baseline and gets no air-leakage adjustment.
² Conduction only (framing, no air leakage). Nominal: 5.5" x R-3.6/in open-cell = R-19.8; 5.5" x R-6.1/in closed-cell = R-33.6 (U.S. DOE Building America spray foam guide). Effective: ASHRAE parallel-path at a 25% framing factor (2x6 @ 16" o.c.), stud R-1.25/in, same layers as Intertek's wall. The same math gives R-15.7 for the batt wall (Intertek: R-15). Cross-check, Building Science Corp. RR-0903 THERM whole-wall: R-16.5 (open-cell, 5.5" R-21) and R-19.1 (closed-cell, 5" R-28/29). BSC notes THERM does not credit spray foam's air sealing.
³ Intertek Table 1: effective R-21.07, U-0.047 (2x4 center studs); meets ASHRAE 90.1-2022 U-0.051. Left-side R-21 is this effective value; Intertek lists the EPS core's nominal insulation as R-24 (R-23.93). Intertek's EPS input assumes R-4.35/in at 1.0 pcf. Use of the Intertek name in advertising requires Intertek's written approval. Full sources: sources.md.
