# The most common reason a Midwestern roof fails before its warranty

> Under-ventilated attics cook the shingle from below.

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# The most common reason a Midwestern roof fails before its warranty

Under-ventilated attics cook the shingle from below.

February 9, 2026 · 5 min read

If a thirty-year roof lasts fifteen years, attic ventilation is almost always the reason. Here is what is actually going on up there.

Asphalt shingle is rated for thirty years of service when the deck temperature stays in a normal range. When an attic is under-ventilated, the deck cooks. Summer afternoon attic temperatures in St. Louis can exceed 150 degrees if the airflow is wrong. At those temperatures the asphalt in the shingle softens, the granules loosen, and the shingle ages two to three times faster than its design.

The cure is balanced ventilation: cool air entering at the soffit, hot air exhausting at the ridge. A ridge vent runs the entire length of the ridge and pulls air out passively. Soffit vents along the underside of the eave pull cool air in. The ratio of intake to exhaust needs to be roughly balanced: too much exhaust and you pull conditioned air out of the living space; too little exhaust and the attic cooks.

Most older Midwestern homes were built with one or the other but not both, or with both but at the wrong ratio. When we tear off a roof in St. Charles or O'Fallon, the first thing the foreman checks is whether the existing ventilation is doing its job. Half the time, the answer is no, and adding proper ridge vent and clearing the soffit vents adds maybe four hundred dollars to the install and ten years to the life of the new roof.

If you are not replacing the roof anytime soon but you suspect ventilation is the issue, you can check the attic yourself: on a hot afternoon, climb up and feel the air temperature. If it is more than 20-30 degrees hotter than outside, ventilation is the likely culprit. A two-hundred-dollar attic-fan retrofit is a band-aid, not a fix; the right answer is balanced passive ventilation, and it pays for itself in roof life.

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