Different Roof Types for Ventilation

Peaked Roofs

• Ventilation systems in peaked roofs with pronounced slopes take advantage of the fact that warm air rises. Vents in the soffits allow air to enter under the eaves of the roof; as the outside air is warmed by the air in the attic, it flows upward through the bays between the rafters, which should be left free of insulation. At the peak of the roof, the rising air is vented through an open ridge vent that runs along the peak.

Hip Roofs

• Hip roofs slope inward on all sides rather than on just two sides as is the case with a gable roof. The additional slopes reduce the size of the ridge at the peak of the roof and thus reduce the area available for a ridge vent. Options for providing adequate ventilation in a hip roof include installing ridge vents along the ridges of the sloping hips, using louvers that allow air to vent on the roof's hip ends or installing an electric attic fan to move more air out of the attic.

Flat Roofs

• Flat roofs and those with shallow slopes are difficult to ventilate. Water moves off of them more slowly, making them prone to leaking, so vents must be carefully installed to avoid providing a point of entry for water. Water also more easily flows upward on a low-sloped roof, so wind-blown rain tends to enter through traditional ridge vents. As a result of these challenges, low-sloped and flat roofs are often unventilated, and adequate insulation is crucial to prevent ice dams and water damage.

Slate Roofs

• Peaked slate roofs can be ventilated in the same manner as peaked asphalt-shingle roofs, with soffit and ridge vents. Slate shingles, however, are porous and air-permeable, unlike asphalt shingles, which create an air-tight roof surface. Because of this, slate roofs are able to breathe and are less susceptible to long-term moisture damage to the roof decking.