Proper Attic Ventilation

Listen to the article

Proper ventilation of the attic is important to prevent moisture condensation problems in the attic as well as in other parts of your home. In the winter, adequate ventilation stops moisture from accumulating and damaging insulation, wood framing and sheathing. In the summer, adequate ventilation can reduce your air conditioning load and costs as well as keep your home more comfortable. Inadequate ventilation in a home can result in mold and mildew, growth that may appear on walls, in closets, on furniture, clothing, other linens and elsewhere.

The most efficient system for attic ventilation is non-mechanical and includes intake at the soffit level and at the ridge level. However, in cases where the slope of the roof is three in 12 or less, mechanical systems may be necessary.

How much ventilation is adequate? If your home has a vapor barrier follow the guideline of one square foot of roof or gable ventilation to 300 square feet of attic floor space. If the house does not have a vapor barrier, is unshaded or has a dark roof, more ventilation may be needed.

Marsha Alexander, AlexanderM@missouri.edu
Regional Specialist, Housing and Environmental Design
Jackson County, Missouri
University of Missouri Extension