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Dampness and Mold Growth in Buildings: A National Academy Study

Figure 1. Mold in lab cultures (Photo courtesy of Mike McNickle)

Figure 1. Mold in lab cultures (Photo courtesy of Mike McNickle)

Mold growth in buildings and its possible effects on human health have been in the news for several years while claims against insurance companies for mold and moisture-related problems in buildings have been on the rise, as has mold-related litigation. A recent report by the National Academy of Sciences Institute of Medicine has concluded that strong scientific evidence links mold and damp conditions in buildings to some health effects.

Damp Indoor Spaces and Health, authored by a committee of the same name, was released at the end of May. William Fisk, Senior Staff Scientist and Head of the Indoor Environment Department (IED) in the Environmental Energy Technologies Division (EETD) at Lawrence Berkeley National Laboratory (Berkeley Lab), was a member of the committee. Along with eight other committee members, including Committee Chair and Dean of the University of Michigan School of Public Health Noreen Clark, Fisk participated in an extensive review of the available scientific literature on the subject.

"The committee concluded that there is robust scientific evidence of an association of increases in selected respiratory health effects with building dampness or visible mold," says Fisk. "These health effects are asthma exacerbation in sensitized individuals, and cough, wheeze, and upper-respiratory symptoms in otherwise healthy individuals. The committee also said that building dampness is an important public-health problem because dampness and mold problems are present in a significant fraction of buildings and linked to substantial increases in these health effects.

"However, the committee believes that the existing evidence is insufficient to conclude that there is a causal relationship between dampness or mold and increases in these health effects. For example, moisture itself is not directly causing the adverse health effects, and it is not certain whether exposures to molds or to some other pollutants found in damp buildings actually cause the observed increases in adverse health effects."

Why is Dampness a Concern?

Dampness in buildings is a concern because it often leads to growth of molds and bacteria and to increased emissions of chemicals from building materials. In addition, dampness causes structural degradation of buildings. Dampness in buildings has a number of causes. The report argues that the way to reduce both dampness problems and the risk of associated health effects is to improve the design, construction, operation, and maintenance of buildings.

"There is considerable existing knowledge about how to make these improvements that is underutilized," says Fisk. "For example, many dampness problems are caused by simple water leaks in roofs, walls, and plumbing systems that can be prevented or rapidly corrected through building maintenance."

Mold growing on the wall behind cabinets. (Photo courtesy of Mike McNickle)

Figure 2. Some mold is hidden from view, such as the mold shown in this image, which was discovered when cabinets were removed from a wall (Photo courtesy of Mike McNickle)

A living room in a San Francisco apartment in which the tenant never opened the windows.

Figure 3. A living room in a San Francisco apartment in which the tenant never opened the windows (for security reasons) (Photo courtesy of San Francisco Department of Public Health)

"Toxic molds" in buildings are a specific concern that is not well understood. These molds can, under certain conditions, produce agents called mycotoxins. "Cellular and animal studies have shown that mycotoxins can be highly toxic," says Fisk. "However, we do not know what levels of exposure are necessary to cause health effects in humans, nor the amount to which people are exposed in mold-contaminated buildings."

Research Needs

The National Academy committee identified a long list of research needs related to damp buildings and mold. One need is for a better method to measure people's exposures to dampness-related pollutants. "We also need a better fundamental understanding of how people are actually exposed to microbial agents," says Fisk. "For example, does resuspension of mold spores from floors (as people walk over them) contribute substantially to exposures? The effect of dampness on several types of health problems needs much further research. The health benefits of mold remediation also need to be better understood."

Despite some uncertainties about molds, dampness, and their health effects, the committee concluded that dampness is an important public-health problem and suggested that education, training, and incentives for reducing dampness should be elements of a public-health response.

Berkeley Lab's Contributions

In general, most dampness and mold research has been performed in homes. However, Mark Mendell, an IED epidemiologist, is analyzing data from office buildings to assess whether dampness in those buildings increases the risk of adverse health effects. A recent analysis performed in collaboration with the California Department of Health Services found that increases in lower-respiratory and mucous-membrane symptoms were linked to particularly high airborne concentrations of molds and bacteria that grow on damp building materials.

IED has investigated the relationship between air-conditioning systems and health effects. On average, occupants of air-conditioned buildings have higher rates of a variety of respiratory and other health symptoms. The explanation for this correlation is not clear; one hypothesis is some air-conditioning systems become contaminated with microbial agents transported into the building's occupied spaces. In analyses of data from 80 office buildings where occupants complained of respiratory and related problems, evidence of wet, dirty air-conditioning systems was associated with increased lower-respiratory symptoms such as wheeze and shortness in breath.

In addition to contributing to research on health effects, the IED investigates how pollutants are transported within buildings, the mechanisms and amounts of pollutant exposure in buildings, and the effectiveness of technologies and practices for reducing pollutant exposure in buildings. IED researchers are particularly interested in technologies or practices that can simultaneously improve indoor environmental quality and save energy.

Advice to Homeowners

Fisk offers some suggestions on how to prevent mold from becoming a problem in homes. "The key to prevention," he says, "is to design, construct, operate, and maintain homes in a way that prevents building components and furnishings from becoming unusually damp. Some causes of dampness problems are complex and must be identified and addressed by building experts," he adds. "If you see evidence of significant dampness, such as water stains or water-damaged building materials, you should rapidly take actions to correct the cause of the problem. Often these require the assistance of a building professional, for example, a roofing company for a roof leak."

Some causes and solutions are obvious. When a plumbing fitting under the sink starts leaking, the homeowner can tighten or replace it. Dehumidifiers as well as bathroom and kitchen fans that exhaust air to outdoors can help prevent dampness problems in some situations, but these are not the solution to problems such as leaky pipes, roofs, or windows.

When building materials become wet from a sudden leak or spill, they should be dried as quickly as possible, within hours or a couple of days-not weeks-to reduce the risk of mold growth, Fisk advises. Outside experts will normally be required to dry buildings after large leaks or floods.

"When visible mold is present," says Fisk, "it should be removed by cleaning. When cleaning is not possible, the mold-contaminated materials should be removed. Homeowners can use normal cleaning practices to remove small amounts of mold, such as the moldy spots in the shower, but widespread mold contamination should be addressed by professionals. The most important message to remember," he concludes, "is that controlling building dampness is the key to preventing mold contamination."

— Allan Chen

For more information, contact:

  • William Fisk
  • (510) 486-5910; Fax (510) 486-6658

For the National Academy report, see:Damp Indoor Spaces and Health

There are numerous sources of information on mold control for homeowners. For example, see the U.S. EPA site.

This work was funded by the National Academy of Sciences.

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