Normal household activities, such as doing laundry, running dishwashers, and taking showers, generate warm, moist air. This air rises from the living space into the attic. When the warm, moist air reaches the cooler attic, it condenses, wetting the framing members and insulation. Continuous wetting can damage the roofing and attic materials, causing mold growth. This can lead to respiratory problems for homeowners and eventual structural problems with the roof. If the attic insulation gets wet, its R-value decreases, putting additional strain on the HVAC system and increasing energy bills.

Heat build-up in the attic can also damage roofing materials. In the winter, warm attic air can cause uneven snowmelt on the roof and lead to ice damming. Ice damming occurs when melted snow runs down the roof to the eaves and then re-freezes as icicles. The ice expands and backs up under the shingles, exposing the roofing paper and sheathing to water. This can delaminate the roof sheathing and promote mold growth.

A properly ventilated attic can prevent these problems. The recommended amount of attic ventilation is 1 square foot per 300 square feet of attic area. A system of vents that includes soffit vents, baffles, and ridge vents is the best way to meet this recommendation. These vents work together to facilitate continuous air flow—in through the soffits, up the rafters, and out through the ridges—introducing fresh air into the attic and exhausting warm, moist air to the exterior. Even with no wind, the natural convection action of rising warm air maintains a continuous air flow along the underside of the roof. This vent system works in all climates and seasons, and it doesn’t require any moving parts or energy consumption. Soffit vents, baffles, and ridge vents work together to ventilate the attic:

• Soffit vents. Soffit vents are perforated soffits that are installed the same way as solid soffits. Soffit vents provide better airflow in the summer and protection against moisture and ice buildup in the winter.
• Baffles. Baffles are installed at the eaves. They allow fresh air to flow into the attic from the soffit vents without interference from the surrounding insulation.
• Ridge vents. Ridge vents are installed along the roof ridge to provide uniform ventilation throughout the attic, unlike turbines, louvers, or gable vents. They can be fit to a range of roof pitches.

Excessive heat and moisture in the attic can threaten a home's health. A properly ventilated attic can protect the home from deterioration and mold growth and ensure a more durable, energy-efficient home.

For more Best Practices® in ventilation, sign your team up for Mechanicals: HVAC, an online training course from BuildIQ University, or read this related article called "Keeping Your Attic Cool and Dry."