Summarization of Final Report for ASHRAE Research Project 1365-RP “Thermal Performance of Building Envelope Details for Mid- and High-Rise Buildings”

Morrison Hershefield summarizes the Research project as follows:

(Building energy standards, such as ASHRAE 90.1, force recognition of the impact of thermal bridging)

Adding Batt Insulation

Often, fiberglass batt is added to fill the stud cavity in order to further increase the thermal resistance of an exterior insulated steel stud assembly. To evaluate the benefit of adding this insulation, we modeled the horizontal z-girt arrangement with and without an R-12 batt in the stud cavity. The results show that by adding the R-12 batt in the stud wall increases the assembly R-value by, on average, R-7.5.

These results will differ using other systems; but only slightly. In general, adding insulation in the stud cavity of an exterior insulated stud wall assembly will add approximately 60% of the rated nominal value of that insulation to the thermal resistance of the assembly.

This improvement may seem modest for the increased nominal R-value, but it may be important in meeting code.