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 all cause 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:


Building Air Quality: A Guide for Building Owners and Facility Managers, Environmental Protection Agency, EPA/NIOSH, 1991

Building Air Quality, A Guide for Building Owners and Facility Managers, Appendix C: Moisture, Mold and Mildew, EPA/NIOSH, 1991

Canadian Centre for Occupational Health and Safety, OSH Answers: Indoor Air Quality—Moulds and Fungi

Indoor Air Pressure: Controlling Indoor Air Pressure and Ventilation Rate, Health and Energy Company, Omaha, NE

Institute of Inspection Cleaning and Restoration Certification

Mold Resources, Environmental Protection Agency

Mold and Mildew, Health and Energy Company, Omaha NE

NIOSH Alert: Preventing Asthma in Animal Handlers, 1998

NIOSH Safety and Health Topic: Indoor Environmental Health Quality

NIOSH Safety and Health Topic: Occupational Respiratory Disease Surveillance, State-Based Surveillance

Office Air Pollution: Office Illness, Health and Energy Company, Omaha, NE

OSHA Fact Sheet: Fungi

Quraishi, Arif A. and Neil G. Carlson, “Managing Water Infiltration into Buildings, Public Risk, May/June 1999, Public Risk Management Association

Water Leakage and Mold Checklist