Off-ridge vents are placed below the ridge line of a roof, and they allow hot air to escape from attics, clothes dryers, bathrooms and range hoods. Ridge vents are placed near a roof's peak, and they are often shorter than other vents.
Off-ridge vents are recommended for hip-style roofs. They usually are accompanied by soffit vents, which pull cool air in and circulate it through the attic before the air leaves through the off-ridge vents. For every 150 square feet of attic space, a house needs 1 square foot of ventilation. The required amount of ventilation drops by half for houses that include a vapor barrier under the insulation.