1. Air transport, and

  2. Vapor diffusion.

Bulk transport, or leakage of rain, melting snow, and groundwater through the building envelope, is orders of magnitude more destructive than any other force. Capillary movement of water from the outside of the building into the building through porous surfaces and the movement of air-transported water vapor are second and third in the rank order of transport mechanisms. Both represent a significant threat and require dedicated attention during design and construction. Vapor diffusion is a relatively weak force but also requires careful detailing and execution of building assemblies. Excellent resources for proper moisture control design include The Moisture Control Handbook, Principles and Practices for Residential and Small Commercial Buildings by Joseph Lstiburek and John Carmody (1994) and The Building Foundation Design Handbook (ORNL, 1988).

EXCESSIVE MOISTURE AND HEALTH

Recently there has been concern that indoor moisture “dampness” and mold growth can lead to a variety of health problems in adults and children. The most consistent and convincing associations relate to respiratory disease, especially asthma. Asthma is a disorder of airflow obstruction. People with asthma are subject to episodic wheezing, coughing, and shortness of breath. Although these symptoms are common clinical features of asthma, they are common symptoms of other respiratory illnesses as well. Finding a widely accepted definition of this disease has proved problematic, and the following has been offered as the most acceptable:

Asthma is understood to be a chronic disease of the airways characterized by an inflammatory response involving many cell types. Both genetic and environmental factors appear to play important roles in the initiation and continuation of the inflammation. Although the inflammatory response may vary from one patient to another, the symptoms are often episodic and usually include wheezing, breathlessness, chest tightness, and coughing. Symptoms may occur at any time of the day, but are more commonly seen at night. These symptoms are associated with widespread airflow obstruction that is at least partially reversible with pharmacologic agent or time. Many persons with asthma also have varying degrees of bronchial hyperresponsiveness. Research has shown that after long periods of time this inflammation may cause a gradual alteration or remodeling of the architecture of the lungs that cannot be reversed with therapy. (IOM, 2000, pp. 23-24)

Asthma affects 8 percent to 10 percent of the population and even larger proportions of children in certain cities or poor urban populations. It is a common reason that children are absent from school and one of the most common causes of work absences as well; 14 million days of school loss were recorded in 1994-1996, 3.4 days per child with asthma (Cox-Ganser et al., 2005).

Indoor environments are an important factor in chronic asthma symptoms and morbidity, whether these environments are in the home or in the school. The Institute of



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