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Vent attic to stop condensation

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Question: I have a problem concerning my year-old roof. There is no problem during even severe storms. But whenever we have a cold spell in the winter (anything below 10 degrees Fahrenheit), the nails used to put the roof on and the surrounding attic beams become coated with frost and eventually drip down onto the ceiling of the rooms below. This never happened with our old roof. Is there something we can do to prevent further damage to our ceiling? Is there some way this can be corrected without redoing the whole roof? - A.T., Palos Heights, Ill.

Answer: What you are seeing is the effect of condensation. The moisture levels in the air of the attic are so high that droplets form on the ends of the cold metal nails and on the underside of the wood.

When the attic is warm, the moist air remains above the dew point and no moisture collects.

If you're sure there are no roof leaks, then your problem is one of ventilation. It is more important to vent the attic in the winter than in the summer to keep the moisture from condensing inside the attic. You should have vents in the overhang and high up on the roof at the ridge (peak of the roof) or in the gables.

If you have an electric fan for ventilation, the fan needs a humidistat installed, in parallel with the thermostat, so that the fan works year-round.

If the overhang venting is blocked for any reason, air cannot enter and the attic becomes pressurized so that little or no air can move out of the upper vents.

Also, remember that venting needs to be balanced. For each square foot of free venting at the soffit or overhang, you need an equal amount of venting at the roof or gable ends.

Block off or remove additional sources of moisture. Bathroom and kitchen vent fans need to extend to the exterior. Clothes dryer vents need to be to the outside. If the home has a dirt crawl space at the foundation, cover the earth with a plastic vapor barrier to prevent evaporation and migration of the dampness. Concrete basement floors can be sealed.