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
Conditions for mold growth
- temperature between 40º F and 100º F
- mold spore
- nutrients (most surfaces)
- moisture (standing water, humidity, ?damp?)
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
- 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 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.
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.
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
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
To reduce a vapor pressure-dominated mold and mildew:
- vent air from moisture-generating activities (showers, laundry, cooking) to
- 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)
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
- 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.
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