What You Should Know
About Mold

Molds produce tiny spores, and these spores waft through the indoor and outdoor air continually. When mold spores find a damp spot indoors, they usually start digesting whatever they land on in order to survive. There are molds that can grow on wood, paper, carpet, and foods. When excessive moisture or water accumulates indoors, mold growth will often occur, particularly if the moisture problem remains undiscovered or unaddressed.

We hope you find the following helpful. You will find additional on the websites and booklets cited at the bottom of this page.

Controlling Mold

Although it is virtually impossible to eliminate all mold spores in the indoor environment, you can control mold growth by controlling moisture. 

• It is important to thoroughly dry furnishing and structual materials within 24-48 hours to prevent mold growth.
• If mold has developed, clean it up and get rid of the excess water or moisture. Fix leaky plumbing or other sources of the moisture, wash the mold off hard surfaces with detergent and water, and dry completely. Absorbent materials, such as ceiling tiles and carpet, that contain mold should be replaced.
• Reduce indoor humidity to 30-60% and discourage mold growth by venting bathrooms, dryers, and other moisture-generating sources to the outside. Use air conditioners and dehumidifiers, increase ventilation, and use exhaust fans whenever cooking, washing dishes, and cleaning.
• Prevent condensation on cold surfaces, such as windows, piping, exterior walls, roofing, and floors, by adding insulation.
• Do not install carpeting in areas where there is a perpetual source of moisture such as drinking fountains, classroom sinks, or on concrete floors with potential leaks or frequent condensation.

Moisture control is the key to mold control. One third to one half of all structures have damp conditions that may encourage development of pollutants such as molds and bacteria. These bacteria and molds can spread infectious diseases and cause allergic reactions such as asthma. Excess moisture can come into your home in a variety of ways--a leak, a seeping basement floor, the shower, the dishwasher, and even cooking. The amount of moisture that the air in your home can hold depends on the temperature of the air. As the temperature goes down, the air is able to hold less moisture. This is why moisture condenses on cold surfaces, such as windows, in cold weather. This excess moisture inside your home can encourage biological pollutants to grow.

The following is an excerpt from Biological Pollutants in Your Home prepared by the American Lung Association and the U.S. Consumer Product Safety Commission, EPA Document Reference Number 402-F-90-102, January 1990. This document explains indoor biological pollution, health effects of biological pollutants, and how to control their growth and buildup.

Consider these suggestions to control moisture in your home:

• Fix leaks and seepage immediately.
• If water is entering your house from the outside, your options range from simple landscaping to extensive excavation and waterproofing. Make sure that the ground slopes away from the house.
• Water in the basement can result from the lack of gutters or a water flow toward the house.
• Water leaks in pipes or around tubs and sinks can provide a place for biological pollutants to grow.
• Put a plastic cover over dirt in crawlspaces to prevent moisture from coming in from the ground. Be sure crawlspaces are well ventilated.
• Use exhaust fans in bathrooms and kitchens to remove moisture to the outside (not into the attic). Vent your clothes dryer to the outside.
• Turn off appliances such as humidifiers or kerosene heaters if you notice moisture on windows and other surfaces.
• Use dehumidifiers and air conditioners, especially in hot, humid  climates, to reduce moisture in the air. Be sure that the appliances themselves are not sources of biological pollutants.
• Raise the temperature of cold surfaces where moisture condenses. Use insulation or storm windows. Keep in mind that a storm window installed on the inside is more effective than one installed on the outside.
• Open doors between rooms, especially doors to closets which may be colder than the rooms. This increases circulation which carries heat to the cold surfaces. Further increase circulation by using fans and by moving furniture away wall and corners.
• Be sure that your house has a source of fresh air and can expel excessive moisture from the home.
• Pay special attention to carpet on concrete floors. Carpet can absorb moisture and become a breeding ground for biological pollutants. Use area rugs--check them frequently and wash them often. In certain climates, if carpet is to be installed over a concrete floor, it may be necessary to use a vapor barrier (plastic sheeting) over the concrete and cover that with sub-flooring (insulation covered with plywood) to prevent a moisture problem.

Moisture problems and their solutions differ from one climate to another. The Northeast is cold and wet while the Southwest is hot and dry. The South is hot and wet, and the Western Mountain states are cold and dry. All of these regions can have moisture problems. For example, evaporative coolers used in the Southwest can encourage the growth of biological pollutants. In other hot regions, the use of air conditioners which cool the air too quickly may prevent the air conditioners from running long enough to remove excess moisture from the air. The types of construction and weatherization for the different climates can lead to different problems and solutions.

Moisture On Windows

Excess humidity inside your home for a prolonged period of time can damage walls, especially when outdoor air termperatures are very cold. Your humidistat is set too high if excessive moisture collects on windows and other cold surfaces. 

Other sources of excess moisture besides overuse of a humidifier may be long showers, running hot water for long periods of time,  boiling or steaming foods, certain plants, and drying clothes indoors.

A tight, energy efficient house holds more moisture so you may  need to run a kitchen or bath ventilating fan at times or open a window briefly. Storm windows and caulking around windows keep the interior glass warmer and reduce condensation of moisture there.

Humidifiers are not recommended for use in buildings without proper vapor barriers because of potential damage from moisture buildup. Consult a building contractor to determine the adequacy of the vapor barrier in your house. Use a humidity indicator to measure the relative humidity in your house. The American Society of Heating and Air Conditioning Engineers (ASHRAE) recommends these maximum indoor humidity levels.

Outdoor Recommended Indoor Temperature Relative Humidity:

+20 F. 35%
+10 F. 30%
0 F. 25%
-10 F. 20%
-20 F. 15%

Anne Field, Extension Specialist, Emeritus, with reference from the Association for Home Appliance Manufacturers (www.aham.org/).

Should You Have the Air Ducts in Your Home Cleaned?

You should consider having the air ducts in your home cleaned if there is substantial visible mold growth inside hard surface ducts (e.g., sheet metal) or on other components of your heating and cooling system. There are several important points to understand concerning mold detection in heating and cooling systems:

• Many sections of your heating and cooling system may not be accessible for a visible inspection so ask the service provider to show you any mold they find.
• Although a substance may look like mold, a positive determination can be made only by an expert and may require laboratory analysis for final confirmation. For about $50, some microbiology laboratories can tell you whether a sample sent to them on a clear strip of sticky household tape is mold or simply a substance that resembles it.
• If you have insulated air ducts and the insulation gets wet or moldy, it cannot be effectively cleaned and should be removed and replaced.
• If the conditions causing the mold growth in the first place are not corrected, mold growth will recur.