A hygroscopic material has the ability to adsorb and store moisture from the surrounding air. When the RH changes, a difference in the vapour partial pressure results in the material absorbing or desorbing moisture in order to reach equilibrium. Most materials have a hygroscopic potential which is too low to have any impact on indoor humidity, however this ability can vary to a great extent in building materials and is related to the available surface area/porosity and the nature of the material. A small number of studies have demonstrated that interior moisture buffering by the building fabric can beneficially affect energy consumption, component durability, thermal comfort and air quality (Janssen, H and Roels, S., 2009). Padfield (1998) demonstrated the enhanced moisture buffering potential of clay based materials compared to many other conventional materials. However, there is still a need for wider recognition of these effects, scientific characterisation of materials and development of a rigorous design model or tool to support implementation by industry.
About Helen CornwellHelen Cornwell is the Project Manager for the EU funded project ISOBIO (Development and Demonstration of Highly Insulating, Construction Materials from Bio-derived Aggregates) and Networking Coordinator for the ECO-SEE project (ECO-innovative, Safe and Energy Efficient wall panels and materials for a healthier indoor environment).
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