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Resources / Combat Mold with Moisture Control

The key to mold control is managing moisture.

What is mold?

"Molds are microscopic organisms that are present virtually everywhere in our environment. Molds break down dead organic materials, such as wood and leaves, and recycle nutrients back into the environment. All that is necessary for mold growth to start on these materials is moisture."

Source: "Precautions during construction will save headaches later" by David Chawes, Prezant Associates; Seattle Daily Journal of Commerce"

Preventing Mold

Source: University of Florida

Mold needs four factors to grow: spores, temperature, moisture, and food source.

Mold spores are always present in both indoor and outdoor air, and they can flourish in any ambient temperature from 40F to 100F (4C to 38C). You may not be able to avoid the presence of mold spores, but you can take steps to control the moisture and food sources mold needs.

As part of your overall mold-resistance strategy, follow good moisture management practices. Then choose moisture- and mold-resistant construction materials such as non-paper-faced, fiberglass mat interior drywall products.

For added resistance, choose building components that will retain as little moisture as possible. Moisture-resistant materials will cut down on retained moisture.

Mold Growth In Heating Season

In a heated climate, mold grows on interior surfaces. Typically, the interior surfaces of exterior walls are cool (due to heat loss), while moisture levels within the conditioned space are high. Mold growth can be controlled in two ways:

  • by preventing the interior surfaces of exterior walls and other building assemblies from becoming too cold, and
  • by limiting interior moisture levels. Adding insulation to a wall or ceiling raises the temperature of the inner surface. Controlled ventilation and control of moisture sources limit interior levels.

Source: Home Energy Magazine online, November/December 1995

Mold Growth In Cooling Climate

If exterior humid air comes in contact with the cavity side of cooled interior gypsum board, its relative humidity can rise above 70% and mold growth can occur in the cavity. Impermeable wall coverings such as vinyl wallpaper can make the problem worse by trapping moisture between the interior finish and the gypsum board.

Source: Home Energy Magazine online, November/December 1995

Proper Storage and Handling of Building Products Helps Prevent Mold

  • Keep stocks of lumber, plywood, oriented-strand board (OSB), drywall, and other porous materials in a dry, covered storage area.
  • If the stockpiles are out in the open, and it looks like it might rain, cover the materials with a good tarp, anchored down so that the wind does not blow it off. When the materials are needed, remove them from beneath the cover without allowing the remainder to get wet or damp.
  • Before installing the materials, inspect carefully for water damage, staining, warping, or initial signs of mold growth. Such signs might be visible patches of mold, or simply the musty odor we associate with mold or mildew. Discard any such materials immediately.
  • Install a roof or cover the new construction as soon as practical.

Source: "Precautions during construction will save headaches later" by David Chawes, Prezant Associates; Seattle Daily Journal of Commerce"

Ten Things You Should Know About Mold

  • Potential health effects and symptoms associated with mold exposure include allergic reactions and other respiratory complaints.
  • There is no practical way to eliminate all mold and mold spores in the indoor environment. The way to control indoor mold growth is to control moisture.
  • If mold is a problem in your home or school, you must clean up the mold and eliminate sources of moisture.
  • Fix the source of the water problem or leak to prevent mold growth.
  • Reduce indoor humidity to 30-60%. Decrease mold growth by venting bathrooms, dryers, and other moisture-generating sources to the outside; using air conditioners and de-humidifiers; increasing ventilation; and using exhaust fans whenever cooking, dishwashing and cleaning.
  • Clean and dry any damp or wet building materials and furnishings within 24-48 hours to prevent mold growth.
  • Clean mold off hard surfaces with water and detergent, and dry completely. Absorbent materials such as ceiling tiles that are moldy may need to be replaced.
  • Prevent condensation. Reduce the potential for condensation on cold surfaces (i.e., windows, piping, exterior walls, roof or floors) by adding insulation.
  • In areas where there is a perpetual moisture problem, do not install carpeting (i.e., near drinking fountains, classroom sinks or on concrete floors with leaks or frequent condensation).
  • Molds can be found almost anywhere; it can grow on virtually any substance providing moisture is present. There are molds that can grow on wood, paper, carpet and foods.

Source: National Multi-Housing Council

Other Resources

APA - The Engineered Wood Association

The US Centers for Disease Control (CDC)

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