ASTM C1155 [14]/C1046 [15] and ISO 9869 [16] standards are generally followed in the in situ measurement of the thermal resistance (R-value) and the thermal transmittance (U-value) of building envelope components. The thermal transmittance (Uvalue) is based on the simultaneous measurement of the time averaged heat flux and the differential air temperature, while the thermal resistance is based on the simultaneous measurement of the time averaged heat flux and differential wall surface temperature. The recommendations of ASTM C1060 [17] were followed for the placement of the heat flux sensors and Fig. 4 shows the thermal images of the inside surfaces of the two exterior walls of the test room using an infrared thermographic camera.