Attic Ventilation and Insulation

Almost nobody thinks about the attic when buying a roof, and the attic decides how long that roof lives. A vented attic stays near outside temperature. An unvented one turns into an oven in July and a condensation chamber in January, and both of those eat the roof from the side nobody looks at.

Air In Low, Air Out High

Ventilation is one continuous path. Cool air enters at the soffit vents under the eaves, travels up the underside of the deck, and leaves at the ridge. Break any part of that and the whole thing stops.

• Soffit vents blocked by insulation pushed into the eaves, which is the usual culprit
• A ridge vent installed without the deck being cut open under it, which happens more than it should
• Bathroom fans venting into the attic instead of outside
• A mix of vent types that short circuit each other and pull from the wrong place

What Bad Ventilation Does

In summer an unvented attic runs far hotter than the air outside. The shingles bake from below as well as above and age faster than they were designed to. A thirty year shingle on a hot deck is not a thirty year roof.

In winter warm moist air from the house rises into the attic, meets the cold underside of the deck and condenses. Frost forms on the nail points. It melts on the first mild day and drips onto the insulation, which then insulates nothing. Do that for enough winters and the deck itself starts to go soft.

It Is Usually a Warranty Condition

Read any shingle manufacturer warranty and you will find a ventilation requirement. A failure on a poorly vented roof can be declined on those grounds, which means the homeowner paid for a long warranty and owns a short one.

We count the net free vent area against the attic square footage and put the number on the estimate. If it does not meet the requirement, fixing it is part of the roof and not an upsell afterward.

Questions About Attic Ventilation