Measurement of heat, air and moisture (HAM) phenomena in building assemblies under both controlled conditions and field conditions are difficult to achieve with uniform accuracy and reliability. Care is needed in selecting the measurement sensors and instrumentation to achieve an acceptable degree of accuracy. When the experiments are planned to answer specific questions or to confirm expected responses, the degree of accuracy needed is pre-determined. Proper calibration coupled with appropriate selection of materials can improve the reliability of the measurements, enhance the accuracy achieved, and ensure that the installation has the durability to survive for as long as is needed by the experiment. The field and laboratory experience of the authors in undertaking HAM measurements, particularly those involving transient conditions arising from exposure to real weather, are the basis for the recommendations provided here. The limitations in both undertaking certain measurements and in the interpretation of some data are addressed. The complex of interactions related to the driving forces and changes in material properties prevents experimenters from attributing certain outcomes to particular theoretical assumptions. However, field studies are complementary to carefully executed laboratory studies. As the accuracy of theory increases, there will be an increased need for detailed and accurate field measurements.

The first part of this paper presented classification of Water Resistive Barrier (WRB) products.4 The main purpose of the research reported in this part is not to determine how different WRB products perform under exposure in real assemblies but to evaluate the effectiveness of the existing test methods to characterize moisture performance of WRB products. An additional purpose is to assess what properties should be determined to enable characterization of WRB for use in computer models for heat, air, and moisture (HAM) transport. The investigation determined that the existing test methods do not provide adequate information. Therefore, new methods are proposed with a view to providing a better basis for evaluating WRB performance in wall assemblies.