Dampness and Mold

Much research has been conducted on building dampness. Topics investigated include the causes of excess building dampness, the influence of dampness on indoor biological and organic chemical contaminants, and the effects of dampness and of dampness-related indoor contaminants on people's health. There is also extensive literature on how to prevent building dampness. This document reviews the current scientific knowledge on these topics. The main findings are as follows:

Nature and Causes of Building Dampness

When the materials in a building become sufficiently damp to cause material damage or visible mold growth we often say that the building has a dampness problem or we characterize the building as a damp building. The dampness and mold growth may occur on visible interior surfaces in the building, including within basements or crawl spaces, or be hidden inside walls and air conditioning systems. Building dampness problems arise from a range of sources including, but not limited to, water leakage through roofs and walls, plumbing system leaks, groundwater entry, damp construction materials, high indoor rates of moisture generation, entry of humid outdoor air coupled with insufficient dehumidification, water vapor condensation on cold surfaces of windows and walls, and floods.

Prevalence of Building Dampness

Based on surveys, approximately half of U.S. homes have visible evidence of a dampness problem or mold contamination. The results of other surveys also suggest that dampness and mold are common in schools and office buildings. In a survey of 100 representative U.S. office buildings, 45% had current water leaks. A survey of U.S. schools by the General Accounting Office reported that 30% of schools had plumbing problems and 27% had roof problems; however, the nature of the problems were not described so the prevalence of associated dampness and mold cannot be determined.

Impacts of Building Dampness on Indoor Air Quality

When building materials or furnishings are damp for a sufficient time period, mold and bacteria will often colonize the materials. The molds and bacteria can produce microscopic airborne particles, some containing allergens or chemicals with the potential to induce inflammation in the respiratory system. Molds and bacteria are also sources of odorous volatile organic compounds in the indoor air. High indoor relative humidity in damp buildings also can increase the number of house dust mites present indoors and these mites are an important source of indoor allergens. Many building materials also emit chemicals into indoor air and increased dampness in these building materials may also lead to increases in emission rates of gaseous non-microbial chemicals, for example formaldehyde.

Dampness-Related Health Risks

Indoor dampness or mold in homes, determined visually or via mold odor, is associated with increases in asthma exacerbation, cough, wheeze, upper respiratory symptoms, asthma development, shortness of breath, ever diagnosed asthma, respiratory infections, bronchitis, allergic rhinitis, and eczema. Meta-analyses of published literature often indicate 30% to 70% increases in the prevalence rates of these adverse health effects in homes with dampness and mold. High indoor humidity in homes increases the number of house dust mites present and the allergen from these mites is associated with increases in asthma and respiratory health effects. Dampness and mold in work places and schools are also associated with increased respiratory health effects. The specific agents, e.g., molds, bacteria, or organic chemicals, causing the health effects of dampness and mold are uncertain.

Implication for Good Building Practices

Given the extensive evidence that the risks of asthma-related and respiratory health effects area substantially increased in damp or moldy buildings, an Institute of Medicine Committee that reviewed the risks of damp and moldy buildings came to the following conclusions:

"Homes and other buildings should be designed, operated, and maintained to prevent water intrusion and excessive moisture accumulation when possible. When water intrusion or moisture accumulation is discovered, the source should be identified and eliminated as soon as practicable to reduce the possibility of problematic microbial growth and building material degradation. The most effective way to manage microbial contaminants, such as mold, that are the result of damp indoor environments is to eliminate or limit the conditions that foster its establishment and growth."

The committee also concluded:

"When microbial contamination is found, it should be eliminated by means that not only limit the possibility of recurrence but also limit exposure of occupants and persons conducting the remediation."

This document provides references to key sources of information on practices for prevention and remediation of dampness problems in buildings.