Attic ventilation, underlayment and roof covering comprise the three legs of a long-lasting, effective roof system. If attic air remains trapped and static, the other components of your roof will deteriorate quickly. Because your roof is the most important system for protecting your home, it pays to make sure the attic underneath can properly breathe.
Let’s explore the facts and fiction of attic ventilation.
Fact 1. Inadequate ventilation allows heat and moisture to hang around in the attic.
Moisture confined in the attic soaks into the wooden structures that support or make up your roof. Rafters and decking boards, if allowed to absorb the moisture rising from the interior of the home can warp, giving the appearance of dips or hills on the rooftop. Moisture also tends to delaminate the engineered wood decking sheets causing them to lose their ability to hold nails. Additionally, dark, wet surfaces give life to mold and mildew which can render your indoor air making it hazardous to your health.
As attic air cools, water vapor condenses and drips from above onto the insulation which compacts it and makes it less effective. As the insulation loses its ability to prevent the exchange of heat between the attic and the rooms below, your furnace and air conditioner must work harder to regulate the interior temperature. Eventually, the condensation can drip through the ceiling and run down the walls below.
Excessive summer heat in the attic can affect asphalt shingles by causing blisters. The heat rises through the shingles, and tiny pockets of air expand in the laminated layers causing the top layer to bubble, weakening the top surface. The weakened spots can then be weathered off, leaving holes in the shingles. Heat blisters aren’t covered by manufacturer or workmanship warranties, nor will they be mistaken for hail damage by insurance adjusters
Fact 2. Poor ventilation contributes to ice damming.
Ice damming happens when the underside of the roof deck heats up enough to melt snow which then runs to the eaves where the colder decking refreezes the water. The ice sheet along the eave prevents more runoff from reaching the gutters and draining away. During multiple freeze/thaw cycles, the forming ice can cause separation between the decking and fascia boards, as well as pop the seals on shingles and allow water to run up beneath them. If the water finds an opportunity in the underlayment, it can penetrate the attic and outside walls.
With a well-ventilated attic, this natural occurrence seldom instigates a problem. However, a poorly ventilated attic traps the heat and sets up the conditions for ice damming.
Myth 1. Ventilating the attic will let cold air into my living space.
This is no more true than the walls permitting the air outside to freely chill your house. Your insulation should block the free-flow of cold air downward into the living space just as your walls block the horizontal heat exchange to the best extent possible. Good insulation remains critical no matter what’s happening in your attic.
Myth 2. The architect designed my attic ventilation per code, so I’m good.
Not necessarily. We hope this is true, but how old is the house? Codes have changed along with the materials used in roofing products. Also, ventilation systems differ depending on the type of covering used on the roof. A house designed originally for wood shakes or tile that now sports asphalt shingles or stone-coated steel probably needs a ventilation assessment.
While the optimal time to assess and adjust your attic ventilation comes when it’s time to replace the roof, it can still be done between re-roofs. Exterior Building Solutions can investigate your roof and attic ventilation at any time. Please call us to schedule your consultation today.