Back to Blog Education Attic Ventilation: The #1 Thing San Antonio Roofers Don't Talk About
Mark WhiteSeptember 15, 20256 min read Here's a roofing secret that most roofers won't tell you because it's not sexy: proper attic ventilation affects your roof lifespan more than the brand of shingles you choose. I've seen premium $20,000 roofs fail in 12 years because of bad ventilation, and $12,000 roofs last 25 years because the attic was properly set up.
In San Antonio's climate, this isn't optional, it's critical.
What Happens in an Under-Ventilated Attic
On a 100°F San Antonio summer day (so, roughly April through October), an under-ventilated attic can reach 150-160°F. That superheated air bakes your shingles from the underside while the sun bakes them from above. It's a shingle sandwich of destruction.
The results: premature granule loss, curling, cracking, and voided manufacturer warranties. Yes, most shingle manufacturers require adequate ventilation for their warranty to be valid. Install a $25,000 roof with bad ventilation and your warranty might be worthless.
The Simple Formula: Balanced Intake and Exhaust
Proper ventilation follows a simple rule: 1 square foot of net free ventilation area for every 150 square feet of attic floor space (or 1:300 if you have a vapor barrier). Split evenly between intake (soffit vents at the eaves) and exhaust (ridge vent at the peak).
The physics are elegant: cooler outside air enters through the soffits, rises as it heats up, and exits through the ridge vent. This natural convection keeps your attic close to outside temperature without any moving parts or electricity.
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Book Your Free Inspection →Ridge Vent vs. Box Vents vs. Power Fans
Ridge vent is the gold standard for exhaust ventilation. It runs the entire length of your roof peak, providing uniform ventilation with no moving parts to fail. Every roof we install at Legacy gets continuous ridge vent.
Box vents (also called turtle vents or static vents) work but create uneven ventilation, great airflow near the vent, dead spots everywhere else. They're better than nothing but inferior to ridge vent.
Powered attic fans are the controversial option. They work, but they can create negative pressure that actually pulls conditioned air from your living space through ceiling penetrations, making your AC work harder. In most cases, proper passive ventilation (ridge + soffit) outperforms powered fans.
The Radiant Barrier Bonus
While we're talking about attics, consider a radiant barrier if your home doesn't have one. A radiant barrier is a reflective foil layer that reduces radiant heat transfer from your roof to your attic by up to 97%. In San Antonio, a radiant barrier can reduce cooling costs by 5-10% and reduce attic temperatures by 20-30°F.
Cost: $800-$1,500 for a typical home, installed. We can add it during any re-roof project for minimal additional cost since we're already up there.
Questions about ventilation? Legacy Home Improvements includes a ventilation assessment with every free free roof inspection. Call (210) 272-7272.
Got a roofing question? Something keeping you up at night? (Besides that mysterious dripping sound?) Email me personally at mwhite@legacytx.com. I read and answer every single one.
MW Mark White
Owner, Legacy Home Improvements · San Antonio since 1999
Mark has been in the roofing business for over 25 years. He personally inspects homes, works with insurance adjusters, and answers every email at mwhite@legacytx.com.
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