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Condensation Problem on Walls & Ceiling

Q. We have condensation forming on the ceiling and lower wall in a bedroom in the back our house. There are droplets of water on spots of the ceiling towards the back corner where the ceiling meets the wall. Along with the water, we are experiencing much mold growth in the same room along the ceiling and lower wall. The mold growth is worse along the lower wall in the corner of the room. In addition, the mold growth is now forming along the windows of our home and there is an unusual amount of condensation and water along the windowsills.

Now here's the perplexing part. This condensation only forms in the cold months when the heater is on (We have radiant heat throughout the house). It does not get better or worse when it rains. It does not occur in the spring or summer, even when it rains.

We have had 2 roofing companies inspect the roof, and both found the roof to be in decent repair. We replaced the flashing around 2 skylights and it made no difference. which has not made a difference. We had a carpenter look at the interior and he thinks there may be a pipe releasing steam in the wall, even though it's a perimeter wall with no bathrooms, kitchen, or laundry room connected. Another roofing company is bidding the replacement of our attic installation and a turbine cutout, although they aren't certain this will fix the problem.

Mr. Mosby, we tried your call-in program on KMOX but were unable to get through. Please sir, if you have had dealings with these types of problems, or know of a specialist that has, maybe you could steer us in the right direction.

A. I hear the answer in your question. It is condensation that you describe and by definition, it is moisture "condensing" out of the air into water droplets when the moist air inside your house "touches" the cold exterior walls. This is the same thing as water on the inside glass of windows in the winter. There is likely no leak, no pipes, no error. This is just the law of physics manifesting itself on your cold walls.

This is very common in St. Louis masonry structures. The water droplets form from the moist air in your house. Check your house interior with a moisture meter (just a simple one from a hardware store)for relative humidity in your house. Your relative humidity in your house should be between 30% and 55%. Higher than that indicates too much moisture in the air. If too high, then check for a source for the excessive moisture.

Likely your moisture is below 55%. Radiators heat things but don't actively circulate air. The solution is to circulate the air in the house or rooms with a fan or fans. Wash the walls to remove the mold and mildew and bleach the affected surface. Then make sure the air moves across these surfaces on a continual basis so the moist air does not stagnate and sit against the cold walls and condense the moisture back into water droplets.

This is a serious problem with a simple solution. Don't tear out any plaster or walls until you check the inside air for relative humidity and try my suggestion!

P.S. This is one of the most commonly asked e-mail questions I answer. Simple issue with lots of fear mixed in.

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