“Standard 90.1 requires that U-factors (and air leakage) for doors be determined in accordance with the NFRC rating procedures. All NFRC ratings are based on the whole product, including the frame.”
Consequently, for compliance with Standard 90.1, door U-factors must be:
- either determined in accordance with NFRC 100 or
- assigned the default values in Section A7.1.
Both the NFRC 100 and the Section A7.1 values are for the overall door area, including the door slab and the door frame.
In the same way that some window manufacturers only refer to the center of glass performance (and to ignore the thermal bridging through the window frame), door manufacturers have preferred to talk about the door slab only (and to ignore the thermal bridging in the frame). However, Standard 90.1 requires whole product ratings in accordance with NFRC 100.
The bottom line from a strict 90.1 and IECC perspective is that if the U-factor is not developed using NFRC 100, the default values in Standard 90.1 must be used. These defaults are available in COMcheck and can be used. They represent very poorly performing doors, which can be an issue for some buildings if the door area is a significant fraction of the wall area.