Thermal resistance measurements of an insulated concrete block wall were conducted using a calibrated hot box at four different mean temperatures. The hollow concrete block wall was insulated by installing partial-size inserts composed of expanded polystyrene insulation with reflective air spaces into the cores of the blocks, The thermal resistance measurements were compared with the ASHRAE isotherrnal plane and parallel path methods, The isothermal plane method underpredicted the thermal resistance by 3.5%, whereas the parallel path method overpredicted the thermal resistance by 25.2%.

The isothermal plane method was subsequently used to calculate the therrnal resistance of uninsulated concrete block, concrete block with full-size insulation inserts, and concrete block with partial-size insulation inserts. Both ways of insulating the concrete block increased the thermal resistance of the uninsulated block by more than a factor of three. The use of a full-size insulation insert provided a 10% larger thermal resistance than a partial-size insulation insert with reflective air spaces.