This paper discusses the types of instrumentation that can be used for the in-situ measurement of the thermal resistance of building components. Four types of instrumentation are described: noncontact spot radiometers, contact heat flow transducers, portable calorimeters, and a type of portable guarded hot plate device developed by Lawrence Berkeley Laboratories, called an envelope thermal testing unit. A brief description of each device is given along with a description of how the device is used to measure in-situ thermal properties of building components. A theoretical justification of the use of long-term averaging of the heat flow and temperature data for estimating the thermal resistance is also presented. The accuracy of each in-situ measurement method is accessed.

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