Indoor Humidity, Condensation and Mold

• The EPA advises keeping indoor relative humidity below 60%, ideally between 30% and 50%.
• Wet or damp materials should be dried within 24 to 48 hours to help prevent mold growth.
• Condensation forms when warm, moist air touches a surface colder than its dew point, such as winter windows or cold water pipes.
• Cleaning mold without fixing the moisture source means it will come back.

Use exhaust fans in bathrooms and kitchens, vent clothes dryers outside, fix leaks promptly and use a dehumidifier or air conditioning in humid seasons. Insulating cold surfaces reduces condensation.

The EPA's guidance says an area of mold smaller than about 10 square feet (roughly 3 ft by 3 ft) can usually be handled by the homeowner; larger areas, or mold caused by sewage or contaminated water, call for professional help. Hard surfaces can be scrubbed with detergent and water and dried completely.