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ABSTRACT
As moisture-related problems increase in homes, the need for sensors to accurately measure the moisture level in the building envelope grows. Sensors are needed to assist in model verification, to indicate the effectiveness of moisture abatement steps, and to warn of potential moisture intrusion. The most popular sensors currently used by building scientists are those based on electrical resistance, but a great deal of dissatisfaction exists with this technique. Installation of these sensors is difficult, drift in the response causes transient changes in the measurements, and calibration has proven to be a challenge. Numerous techniques promise better accuracy and easier use than the electric resistance probes, but work is needed to produce a sensor small enough to fit unobtrusively in a wall cavity. This work has identified many existing techniques for measuring moisture and presents advantages and disadvantages of each.
INTRODUCTION
Building practitioners have a significant need for in situ moisture content sensors to help alleviate the problems associated with excess moisture accumulation in buildings. Such problems can lead to mold and mildew growth, structural decay, loss of thermal integrity, and pest infestation. Numerous theoretical models have been proposed to predict the transfer of moisture in buildings, and accurate sensors are needed as a research tool to verify the results of these models, especially when new types of construction or materials are proposed. Sensors are also necessary as a field tool to judge the effectiveness of moisture abatement steps taken in structures. The ultimate use for moisture sensors would be as a predictive tool in a "smart" home that would indicate moisture anomalies so that adjustments could be made to the heating and ventilation systems or repairs could be made to prevent any further problems.
The term "moisture content" refers to the amount of water present in a solid material. The amount of water present in air, on the other hand, is indicated by such quantities as the relative humidity, humidity ratio, or partial pressure of water vapor. The standard test method for measuring the moisture content of wood is documented in ASTM D 4442 (ASTM 1992) and ISO 12570 (ISO 2000) and is representative of a typical method for all building materials. In this method, the weight of the specimen at the...