Published: Jan 2009
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UNCONTROLLED MOISTURE IS THE MOST PREvalent cause of decay in historic buildings. Over a long period of time, the presence of moisture in all of its forms can erode, rot, corrode, and otherwise deteriorate aging building materials if it is not controlled. Historic buildings are vulnerable to moisture damage for several reasons: building materials are fragile, exterior envelopes are not tight, construction joints have weakened over time, modern aggressive methods used to control moisture often further damage historic materials, and modern insulation and HVAC systems used for energy efficiency often create additional moisture problems. And so we see with historic buildings that moisture management is often more complicated than with newer structures. This chapter briefly discusses, in laymen's terms, moisture sources and preservation philosophies and identifies in checklist form the typical patterns of decay for historic buildings and outlines generally acceptable remedial treatments to manage unwanted moisture . Historic buildings, by their very nature, are irreplaceable and dedicated owners see themselves as stewards of their architectural resources. With a renewed emphasis on sustainable design, historic buildings, well-maintained or rehabilitated for continued use, play an important role in conserving our cultural and architectural heritage. If buildings are not maintained, or if moisture is improperly diagnosed and treated, buildings may decay beyond the point that makes economic sense to repair them. ASTM standards are an important component of good repair or replacement specifications. Specific ASTM standards, for example, concerning the use of stainless steel anchors or lime-based mortar mixes, are not listed in this chapter, as each building presents unique circumstances and must be evaluated accordingly. A treatment or ASTM standard for one building may be completely inappropriate for another. While a number of remedial treatments may be listed under the various components of a building, the reader should be aware that careful evaluation must be made by qualified professionals and complex moisture issues generally require a team of specialists knowledgeable about historic construction. This team may include any or all of the following: historical architects, architectural historians, soil and geo-physical engineers, structural engineers, preservation consultants and contractors with proven experience with historic buildings and sites.
Park, Sharon C.
Associate DirectorChief, Smithsonian InstitutionNational Park Service, Washington, DC,