Indoor Air Quality (IAQ)
Control of Moisture and Mold
Fact Sheet
This fact sheet will provide ideas for control of moisture and mold and references for additional
information. If you can control the moisture, then you can control mold. However, keep in mind that
your home is a system. If you change something in one area, there can be unintended results in another
area. As you make changes, be alert to new and different problems. Your eyes, ears, and nose are the
primary instruments that you will need to monitor for mold. However, there are a couple of meters that
can make helpful measurements.
There are many considerations for controlling moisture for good indoor air quality. A good building
design will help reduce moisture problems. Even with an adequate building design, good operation and
maintenance of the building is essential. If your existing home or building has mold or other air quality
problems, additional devices can be installed or new procedures implemented to help address these
Humidity is the amount of moisture or water vapor in the air. People produce moisture when they
breathe or perspire. People add water vapor to indoor air through routine household activities such as
cooking, showering, bathing, doing laundry, and dishwashing. People need humidity for our comfort
and health, but too much or too little humidity can produce a host of difficulties.
Measuring Humidity. You can use a hygrometer to measure relative humidity. A hygrometer is an
inexpensive, easy-to-use instrument, sometimes called a humidity sensor or relative humidity indicator.
You want to keep your humidity between 30 to 50 percent. When it is cold outside, you may need to
reduce your inside humidity in order to avoid problems with moisture and mold.
Condensation occurs when warm, moist air comes into contact with a cold surface. As the temperature
of the colder object gets colder, it takes less humidity in the air to produce condensation. This is why
you may need to reduce your indoor humidity during the winter. You want to watch for condensation
on windows or walls.
Measuring Condensation and Moisture. Walls can have excess moisture that is not easy to see or feel.
A moisture meter might be helpful for identification of moisture.
Ventilation will help control moisture and it will reduce other air pollutants that can build up in the
Exhaust-Only Ventilation: An exhaust fan can be installed near sources of moisture and air pollution.
Bath Vent and Exhaust Fans clear the air in your bathrooms Kitchen Range Hoods vent steam and
cooking odors from the range and stovetop area of your kitchen. Make sure the range hood is ducted to
the outside. Many times range hoods are designed to just circulate the inside air.
Heat-Recovery Ventilation: With the exhaust only ventilators you lose heat along with the air pollution
and moisture. A Heat Recovery Ventilator uses internal fans to pull fresh air in and move stale air out of
a home. The Heat Recovery Ventilator core heats the incoming fresh air, recapturing 60 to 80 percent of
the conditioned temperatures that would otherwise be lost.
Ceiling Fan: A ceiling fan can be used to move warm air dry air into cooler parts of the room. If the
ceiling fan is run in “reverse”, it will move the air from under the fan towards the walls of the room.
Since the fan is blowing up, there will be no draft to room occupants.
Caution: When using exhaust-only fans, combustion appliances (wood burning stoves, diesel
stoves) may be impacted. If there are not enough fresh air intake sources, pollutants could be
pulled into the home through the combustion appliance (called a back-draft).
If humidity cannot be controlled with ventilation alone, perhaps you will want to consider a
dehumidifier. A dehumidifier does not remove air pollutants, but it can remove excess moisture.
Using a dehumidifier in a cool, damp area can help treat humidity-related problems. The dehumidifier
uses a fan to pull room air over two sets of refrigerant-filled coils, one cool and the other warm,
wringing out moisture along the way. The water that condenses out of the air typically drips into a
bucket inside the dehumidifier.
Molds can gradually destroy the things they grow on. You can prevent damage to your home and
furnishings, save money, and avoid potential health problems by eliminating mold growth. Controlling
moisture is the best way to avoid mold growth. However, if you already have mold growth, you may
need to remediate the mold.
If there is mold growth in your home, you must clean up the mold and fix the water problem. If you
clean up the mold, but don't fix the water problem, then, most likely, the mold problem will come back.
The US EPA website has additional information on mold remediation.
Actions to Control Moisture
- Clean, disinfect, and dry surfaces.
- Check for water leaks; if found, repair and clean
any moisture damage caused by the leak.
- Reduce moisture in the home by using ventilation
at the source of any moisture.
- Use an exhaust fan or open window when
showering or washing dishes.
- Vent clothes dryers, stoves and other appliances
that produce moisture to the outside.
- Increase air movement and ventilation.
- Keep appliance drip pans clean.
- Move furniture away from cold outside walls to
allow more air circulation.
- Consider sealing windows with another layer of
plastic or glass.
- Add insulation to reduce cold spots in the building.
Procedures to Clean Small Mold Problems
- “Small areas” of mold can be cleaned with a
detergent solution.
- Wear a mask, safety goggles and rubber gloves.
- Clean “moderate areas” of mold, but wear
proper protective equipment and follow
- Seek professional help if there is a lot of mold
or if mold comes back after cleaning.
Bleach is NOT recommended. The most
compelling reason for advising against bleach is
that fumes are air pollutants, but in addition,
overuse of bleach will result in increased releases
of chlorinated effluents which can be harmful to
the environment.
The URLs that include products or instruments are provided as examples only. An Internet
search engine can help you investigate options, if you plan to make a purchase. We do not
recommend or endorse specific brands or products. We do recommend that you consult with your
Village Environmental Coordinator to see what products and instruments have been used
effectively in your village.