AC-83-12-3 -- Calculated versus Measured Thermal Resistances of Simulated Building Walls Incorporating Airspaces PDF

Thermal resistances of simulated building walls with and without airspaces were measured in a large calibrated hot box facility, and the results were compared with design thermal resistances calculated from the component values listed in ASHRAE tables. Measured and calculated values for walls without airspaces were in good agreement, but measured values were significantly lower than calculated values for most walls incorporating airspaces. The data show that the thermal resistances of typical airspaces in construction are significantly lower than literature values for perfect airspaces, and direct use of such values in design calculations can lead to serious error.