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
- temperature between 40° F and 100° F
- mold spore
- nutrients (most surfaces)
- moisture (standing water, humidity, “damp”)
Spores
Outdoor and indoor air almost always contains spores. Most commonly used construction material and furnishing can provide nutrients, which are enriched by dirt.
Sanitation
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.
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
- Musty smell
- Moisture on windows and walls
- Mold on books, shoes and other items
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.
- Northeast states are cold and wet.
- Southwest states are hot and dry.
- Southern states are hot and wet.
- Western Mountain states are cold and dry.
Reduction
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:
- raise the temperature near surfaces by raising the thermostat or increasing air circulation (rearrange furniture, install ceiling fans), or
- decrease the heat loss from the surfaces by adding insulation (storm windows) or by closing cracks in the exterior walls (caulk windows, repoint bricks).
To reduce a vapor pressure-dominated mold and mildew:
- vent air from moisture-generating activities (showers, laundry, cooking) to the exterior.
- dehumidify the air (portable room units or forced-air furnace mounted units with self-cleaning drain pans)
- during heating periods, dilute moist warm indoor air with cool and lower-humidity outdoor air (open the window)
Recommendations
To deprive molds of the moisture they need to survive and thrive:
- When the cause of the water leakage has been traced, take immediate steps to remove it. Vacuum or mop up standing water, adjust the HVAC, and/or activate electric fans to speed up the circulation of air. Fix plumbing or roof leaks. If dehumidifiers are available, they should be employed with both HVAC and fans.
- Make sure the ground slopes down at least 6 inches within the first 10 feet from each exterior wall.
- Prevent seepage by correcting roof, gutter or drainage problems. Make certain that rain water drains away from the building quickly enough to prevent saturation of walls and floors that contact the earth.
- Use a properly sized air conditioner for the room or building space.
- Use an electrically powered dehumidifier or a natural gas desiccant dehumidifier to keep indoor relative humidity below 50 percent (as measured in the middle of rooms) and below 60 percent near the coolest surfaces.
- Remove excess humidity from the kitchen, laundry and bathroom by using an exhaust fan or opening a window.
- Cover pots while cooking.
- After taking a shower, wipe water droplets from the shower walls into the drain.
- Hang wet laundry outside or use a clothes dryer vented to the outside when indoor humidity is high.
- Insulate any cold water pipes that have a visibly damp exterior.
- Create a vapor barrier: Lay plastic over dirt in crawl space.
- If using a central humidification system, ensure that it is properly maintained and check frequently to avoid over humidification. Maintain indoor humidity levels between 40 and 60 percent.
- The widespread practice of shutting down ventilation systems during unoccupied hours should be stopped. Instead buildings should continually be slightly pressurized to prevent infiltration of moist air. Some dehumidifiers can help you control humidity and provide necessary ventilation at the same time.
- Do not block air vents or grills.
- Avoid storing papers, clothing, or other “mold food,” in contact with basement floors or outer walls where their moisture content could become high enough to initiate mold growth.
- Use care to prevent excess moisture when cleaning upholstery, carpeting or rugs. Dry quickly.
- Don’t install carpeting in areas where there is a perpetual moisture problem (drinking fountains, sinks or on concrete floors without proper vapor barrier and sub flooring.
Resources
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
