Why Should I Care About Attic Ventilation?

Roof Ventilation

St tham Why Should I Care About Attic Ventilation?


What is it?

Ventilation is the proper airflow into and out of the house through parts of the roof that were purposefully left open during its construction. That flow of air is called the air exchange.


Why is it important?

  1. The “balloon effect” – The temperatures in a trapped attic in San Antonio continue to rise throughout the day, and the hot air will NOT be able to get out of the attic. If your attic is not “properly ventilated”, the pressure will build as the day gets hotter (literally acting like a balloon) pushing hot air into the living space.

    Your roof will begin to expand like a Balloon.
  2. Electric bills go up – Your air conditioner will constantly struggle to keep up when it should actually only be running half the time. The hot air being pushed into theliving space will also cause your electric bills to go up.

    Energy bills will be higher due to improper ventilation.
  3. Cuts your roof life in half – If the attic is not ventilated properly before the summer hits, then the attic acts like an oven, heating the shingles, tiles, metal – even the wooden beams that are part of the structure of your house! I’ve seen plenty of roofs that were warped because they were never properly ventilated.

    Shingles will begin to curl because of the amount of heat trapped in the attic.


“Your attic MUST be significantly cooler through proper ventilation than the top of your roof exposed to the beating sun.” – David


  1. Mold, Mildew and Structural Problems – Major problems also develop in an attic with poor ventilation during the winter. Your warm living space leaks warm air into the attic which produces moisture. The moisture then causes mold and mildew to develop on the rafters and decking holding up your roof, which will quickly deteriorate the wood, causing major structural problems.
  2. Kills your warranty – Lastly, a poorly ventilated attic can ruin your warranty on your existing roof. Many roof manufacturers will warranty their shingles up to 30 years. The most common is a 20 to 25 year warranty. So if the roof is under that age and is not properly ventilated, it may cost you the warranty.


My fellow San Antonians! Please heed the warning… proper ventilation is THE key to preventing roof repairs and/or costly roof replacements.


So call us to help you determine if your roof has proper ventilation!


If you’re a techy roof geek like me, here’s more info you may be interested in:       

Tools you will need to calculate proper ventilation for the San Antonio area.

  1. Tape measure. Ideally a 100’ tape
  2. Pen and paper
  3. Calculator
  4. Possibly a ladder

Step 1. Measure roof line, length X width.

Example. 30’ wide X 80’ long = 2400 sq.ft.

Step 2. Divide Sq Ft by 300

Example 2400 divided by 300= 8

Recommended free ventilation area required for the Roof is 8 sq.ft

Step 3. Convert sq.ft. to inches by multiplying by 144.

Example, 8 X 144= 1152. You need 1152 sq. inches

You will need total 1152 sq.in. for a San Antonio roof.

Step 4. 1152 is total needed for roof ventilation.

Example: Divide by 2 to determine intake and exhaust. 1152 divided by 2 = 576 sq.in each inlet and exhaust vents.

Step 5. A standard Exhaust vent is 60 sq.in.

Example: 576 divided by 60= 9.6

In total, you will need a total of 10 Standard roof vents.

Step 6. Choose your vent type!
There are many different roof vents out there so be sure to check the sizes before you buy.


My next blog will address the best exhaust vents to have.


Thank you for reading,

David, aka the “Professor”


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