A Moisture Index to Characterize Climates for Building Envelope Design

Premature failures of building envelopes in the 1990s, notably in coastal areas of North America, point to problems with Moisture management by Exterior Wall Systems (MEWS)1. The MEWS Consortium sought to combine field experience with lab testing and hygrothermal modeling to understand and deal with these problems. The method proposed in this paper was used in MEWS to (1) characterize climate with respect to the risk of related building envelope problems, (2) select locations of interest for a detailed hygrothermal parametric study, and (3) to select moisture reference years for the parametric study (not covered in this paper). This paper describes a method proposed for mapping North American climatic regions according to moisture loading on one hand, and the potential for drying on the other. The composite Moisture Index can be used either with hourly records or summary data and shows promise for application to specific problems, such as decay or corrosion, depending on the nature and mechanisms of the problem being investigated.

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