spread and more severe and thus increase the urgency with which prevention and interventions must be pursued.

INDOOR DAMPNESS

Almost all buildings experience excessive moisture, leaks, or flooding at some point. Research regarding the sources and causes of indoor dampness was addressed in detail in a previous IOM report (2004), which described how and where buildings become wet; reviewed the signs of dampness, how dampness is measured, and what is known about its prevalence and characteristics, such as severity, location, and duration; discussed the risk factors for moisture problems; reviewed how dampness influences indoor microbial growth and chemical emissions; cataloged the various agents that may be present in damp environments; and addressed the influence of building materials on microbial growth and emissions. That effort’s findings are briefly summarized below.

Dampness—a term used to describe a variety of moisture problems, including high relative humidity, condensation, water ponding, and other signs of excess moisture or microbial growth—is prevalent in residential housing. The prevalence and significance of dampness are less well understood in nonresidential structures, such as office buildings and schools, than in residential buildings.

There is no single cause of excessive indoor dampness, and the primary risk factors for it differ among climates, geographic areas, and building types. The prevalence of dampness problems appears to increase as buildings age and deteriorate, but some modern construction techniques and materials and the presence of air-conditioning can increase the risk of dampness problems. The prevalence and nature of these problems suggest that what is known about their causes and prevention is not consistently applied in building design, construction, maintenance, and use.

DAMPNESS AND HEALTH

Efforts to quantify the effects of indoor environmental factors on human health often rely on markers of dampness indoors to characterize risk. This approach reflects recognition that indoor moisture is associated with adverse health outcomes and that exposures to emissions from mold, bacteria, and damaged materials increase when indoor environments are chronically wet or damp.

There have been three large-scale reviews of the relationship between indoor dampness and human health in the past decade. In 2004, IOM issued Damp Indoor Spaces and Health. The World Health Organization (WHO) released WHO Guidelines for Indoor Air Quality: Dampness and



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