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How roof vents work

Roof vents do a lot of work to keep you and your house in good shape. They help keep the house cooler in the summer, and help prevent water damage in the winter. Here’s how.

In the summer, they help keep the attic from becoming an oven (which can make the rest of the house hot, too) by allowing the hot air and humidity to escape the house.

In the winter they do the same job, with different results. Ice damming occurs when warm air from the house gets past the insulation and melts snow on the roof. The water rolls down the roof to the eaves — which are much colder — and freezes. As layers of ice creep up, new water coming down can work its way under the shingles and into the rafters (and even into your house). Good insulation (R40) is the first line of defence. After that, good venting allows the warmer air to escape before it can melt the snow. Ventilation also allows humidity from the house to escape before it condenses on cold nails and wood inside the attic, causing more water damage.

Common vents include gable vents, those louvered windows in the attic gable, and flat passive roof vents, which provide reasonable circulation. Ridge vents, which run the length of a gable roof’s ridge, give better coverage, and turbine vents turn with the wind to draw air up and out faster.

The final link, which helps all these vents work better, are soffit vents, which allow air to come in from under the eaves.

If you have a cathedral ceiling, make sure you allow enough room for good insulation and you install channels between the rafters to allow air to come up from the soffits and out the vents near the peak.