Published: Jan 2009
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WATER, WHICH IS ABUNDANT ON OUR PLANET, naturally undergoes various physico-chemical processes and interacts with all living and nonliving entities. As much as water is essential for all life forms, it can also cause the degradation of many natural and manmade materials. This may be due to chemical, biological, or mechanical processes undergone by the material as a result of its interaction with water. Corrosion of metals is an example for chemical deterioration, decay of wood and wood-based material for biological, and cracking and spalling of masonry material for mechanical. Buildings that are constructed to last many decades include a number of materials that are susceptible to deterioration due to their interaction with moisture. Hence, building researchers, designers, and practitioners have always been interested in the role of moisture in the built environment. The scientific and technical knowledge that is necessary to understand and interpret the consequences of the interaction between moisture and building materials was originally based on the work done by soil scientists [1–3]. In such an approach, building materials are regarded as porous bodies, like soil. The analogy is useful, but inadequate for building applications. Materials in the built environment simultaneously experience three inter-related transport processes: • Heat transport • Moisture transport • Air transport The last is often not an issue in soil science. During the past three decades or so, the approach from soil science was extended to understand the combined heat, air, and moisture (HAM) transport in building materials and components through major international collaborations [4–6] and through the efforts of researchers at major building research organizations. The knowledge that is available today can reasonably well answer questions such as: 1. How can the transport of heat, air, and moisture through building materials and components be predicted? 2. How can the harmful accumulation of moisture in building materials and components be prevented? 3. How do air and moisture transports affect the energy efficiency of buildings? More recently completed international collaborations  are expected to apply the knowledge to improve HAM analyses at the whole-building level. Over the past three decades significant advances have been made in the experimental and analytical methods to determine the hygrothermal behavior of building materials and components as influenced by HAM interactions [8–14]. Later chapters in this handbook deal with various aspects of hygrothermal behavior of building materials, components, and systems individually. This chapter is intended to summarize our present knowledge of moisture storage and transport in building materials. This knowledge is fundamental to understand the complex interaction of heat, air, and moisture transport in the built environment.
Kumaran, Mavinkal K.
Principal Research Officer, National Research Council Canada, Ottawa,