Proper Venting for an Attic
Attic ventilation is necessary to prevent the problems associated with excess moisture. However, what is necessary for proper attic ventilation is not necessarily the same as what is necessary for proper ventilation in other parts of the home, such as crawl spaces and basements. Moreover, while proper ventilation helps prevent problems associated with excess moisture, other measures may be necessary as well. Does this Spark an idea?
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Moisture Problems
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Without proper ventilation, attics will develop moisture problems. As warm air rises in your house, it becomes trapped in the attic because roofing materials are designed to prevent moisture from escaping. Excess moisture in the attic may lead to wood rot, peeling or blistering paint, condensation, mold and mildew growth, musty odors and insect infestation.
Vent Types
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Attic vents can be divided into three groups: power vents, turbines and gravity vents. Power vents and turbines are not desirable for attics in northern climates. Among gravity vents, four types are commonly used in attics: eave, also known as soffit; gable; roof, and continuous ridge.
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Vent Placement
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The most effective and efficient ventilation involves the use of inlet vents near the eaves and outlet vents near the ridge. The vents should be uniformly distributed along the roof and divided between high and low. This will allow warm air to rise and escape through the ridge vents while cool air enters at the eaves. Proper attic ventilation requires 1 square foot of unobstructed ventilation area for every 150 square feet of attic.
Additional Considerations
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Ventilation is only one part of controlling moisture in an attic. For example, an exhaust fan may be necessary to help force ventilation. The capacity of an exhaust fan is determined by the number of cubic feet of air it will move per minute (CFM). To determine the proper CFM for your attic, multiply the cubic feet of the attic by 7 and divide by 60. Other humidity control measures include reducing moisture generating activities -- such as long showers and cooking without lids -- installing insulation and repairing external water problems, such as roof leaks.
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References
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