moisture + mold



What to Know

A water leak or high humidity can lead to mold, mildew, or other biological growth in our homes. Depending on the severity, these conditions can lead to rot, structural damage, premature paint failure, and a variety of health problems. Water can seep into your house from the outside through a leak in your roof, foundation, or small gaps around windows or doors. Water problems can also come from inside your house from a leaking water pipe, toilet, shower or bathtub. High indoor humidity caused by normal activities of everyday living such as showering, cooking, and drying clothes can also be a source of mold, mildew or musty odors.

What to Do

Where does the problem occur? Attic? Basement? Below a bathroom? Ceiling? The “where” can help you identify what is causing the problem. If the problem is localized (a spot on the ceiling, wall or corner) it is possibly caused by a water leak. If the problem is in a large area (a whole wall, room or basement) then it might be caused by high humidity.

Water Leaks

• If a leak is the source of your problem, have it fixed as soon as possible to minimize mold growth.

• If the leak is in your roof, hire a roofing contractor to repair the leak.

• If the leak is from a water pipe, toilet, bathtub or shower, hire a plumber to repair the leak.

• If the leak has caused substantial water damage or mold, you will want to hire a contractor who specializes in mold remediation and water damage repairs.

• After repairing the water leak, dry out the area completely.

• If you have water in the basement or crawlspace, the first place to go to solve it is around the foundation of your home.  Clean rain gutters and redirect downspout runoff away from the foundation.

• Make sure the ground around the house slopes down away from the foundation. If necessary, re-grade so the ground does slopes away.

• If you have a sump pump, make sure it is working properly.
Make sure you cover the sump pump to reduce humidity in the space.  You can make one from a rubber door mat.

• If you have water stains on the ceiling or wall under or near a bathroom it could be a leak from a water pipe, toilet, bathtub or shower. Hire a plumber to repair the leak.


Indoor Humidity

• Do you have a crawlspace under your house? A dirt floor in a crawlspace should be covered with thick plastic (vapor barrier) that is taped at the seams to prevent moisture from the soil increasing humidity levels in your home. If there is standing water or the soil very wet, investigate and resolve how the water is getting in before laying the plastic.

• Use ventilation fans in kitchens and baths to control moisture. Check to make sure ventilation fans exhaust directly outside. In some cases, the vent fan will exhaust into the attic or become disconnected or blocked.

• Your clothes dryer should be vented directly to the outside. Inspect the vent duct. Make sure it is attached securely to the dryer. Check that it is clear of obstructions (i.e. lint). Check for holes that leak air. If the vent duct is damaged and/or made of vinyl, replace it with a metal duct. The vent duct should be cleaned at least once a year.

• Keep air conditioning drip pans clean and the drain lines unobstructed and flowing properly.

• Ask a heating and cooling contractor to check your HVAC system to make sure it is sized and operating properly to remove humidity. If your system is too big or the airflow incorrect, your air conditioner will not remove humidity like it should. Also, ask the contractor to check your duct system for air leaks, and proper size and air flow to each room.

During hot humid months, use a dehumidifier in the basement to reduce condensation on the walls. This may work better after you’ve sealed air leaks to reduce the amount of humid outdoor air that is entering from outside.

Indoor humidity levels between 30% and 50% are ideal.


Additional Resources:


“Because of the LEAP program, we got fans and vents in our bathroom and kitchen and new windows. These measures greatly reduced condensation and mold in our home — a big plus, especially since our daughter has asthma and we are always trying to reduce her symptoms.”
Happy LEAP Homeowner

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