This Design Guide discusses thermal bridging as it pertains to the thermal performance of fenestration systems and their interface with the surrounding conditions, which are now typically part of the glazing subcontractor's scope of work (as determine/assigned by general contractors). Beyond the U-factor of the window or curtain wall itself, how the fenestration system is installed and interfaces with the surrounding wall or roof assemblies can affect the overall thermal performance of the building envelope. 

NOTE: This paper covers thermal bridging at their interface of the fenestration systems with the surrounding perimeter construction/conditions. It does not address thermal performance of the fenestration system itself, as the thermal performance of framing designs and thermal barriers is already accounted for in the overall fenestration U-factor as determined in accordance with NFRC 100 or AAMA 1503. This is the original version of this document. It was approved and published in January 2022.