Frequently Asked Question

Where does the moisture in my attic come from?
Last Updated 10 years ago

Houses are built much "tighter" today than they were 20 or 30 years ago. Windows are more efficient, house wraps are now commonly used, and the R value of insulation has increased. Overall, our homes are more weather-tight. In doing this, we trap moisture in the home. Indoor moisture is generated by many things. The normal perspiration and breathing of a family of four adds about ½ pint of water to the air every hour. Cooking three meals a day adds four or five pints of water to the air. Each shower contributes ½ pint. In fact, every activity that uses water, (like dishwashing, mopping floors, doing laundry) adds moisture to the air. Experts say that the daily living activities of a family of four can add more than 18 gallons of water a week into the air of a home. Air moisture will flow toward drier air to equalize itself. This equalization process actually forces the indoor moisture through the ceiling and insulation into the attic area.

In attics which are not properly vented, moisture is also created by simple condensation. The air inside an improperly vented attic will be warmer than the air outside. When this warmer, moist air comes in contact with the colder roof sheathing, condensation will occur.  In effect, it can actually "rain" in your attic

Remember when installing kitchen and bathroom fans- DO NOT vent them into the attic space.  These heat and moisture sources must be ventilated to the outside to avoid moisture problems in the attic. 

A properly vented attic will keep your attic free of moisture related problems.

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