Fact Sheet

Water Leakage and Mold

Mold and mildew are not only unsightly, but they can trigger allergic reactions and other health problems. The only way to prevent mold is by altering conditions conducive to its growth. For example, paper collections should not be stored in a basement with a low temperature, high humidity, little light and very low air circulation?ideal conditions for the growth of mold. Even if remedial treatment is undertaken, the material will quickly deteriorate again if returned to the environment in which the mold first developed. The following is summarized from the Environmental Protection Agency's advice.

Conditions for mold growth


Outdoor and indoor air almost always contains spores. Most commonly used construction material and furnishing can provide nutrients, which are enriched by dirt.


Cleaning and disinfecting surfaces with nonpolluting cleaners and antimicrobial solutions protects against mold growth, but is it impossible to eliminate all nutrients. Thus, the way to keep mold from thriving and surviving is to control moisture.


Visibly wet surfaces and puddles are obvious sources of moisture that would enhance mold growth. However, high relative humidity and porous materials that absorb and retain moisture are just as supportive. Mold and mildew can be problems in cooling climates as well as heating climates. Either surfaces are too cold or moisture levels are too high, or both. Low-maintenance interior finishes (vinyl wallpaper and other impermeable coverings) can trap moisture between the interior finish and plaster board.

Signs of Elevated Humidity

Liquid and Gas

Water can enter a building as a liquid, a vapor or a gas. Bathrooms, kitchens, laundries, leaks and spills cause the liquid to enter buildings. Water vapor enters the building when water evaporates from the former mentioned causes, and in air exhaled by building occupants, and through the HVAC (heating, ventilation, and air conditioning) system.

Regional Differences

Moisture problems and their solutions differ from climate to climate.


How to treat the problem depends on whether surface temperature or vapor pressure is the dominant cause. Dust adheres to cold spots and can indicate surface temperature domination. Condensation on windows is a sign of vapor pressure domination.

To reduce surface temperature-dominated mold and mildew:

To reduce a vapor pressure-dominated mold and mildew:


To deprive molds of the moisture they need to survive and thrive:


Appendix C Moisture, Mold and Mildew, Environmental Protection Agency

Building Air Quality: A Guide for Building Owners and Facility Managers, Environmental Protection Agency

Mold Resources, Environmental Protection Agency

Mold Growth and Prevention, Health and Energy Company, Omaha NE

Health and safety information with a workplace orientation, National Institute for Occupational Safety and Health (NIOSH)

Water Leakage and Mold Checklist