How much attic ventilation do I need?
Based on the common 1-to-300 rule, split evenly between intake at the soffits and exhaust at the ridge.
Total net free area
720 sq in
Estimated material cost
Ridge vent
20 x $$4.00 per linear ft
$80.00
Soffit vents
7 x $$4.00 per vent
$28.00
Typical store prices before tax and delivery. Change any price to match your store.
How to measure
Measure the length and width of the attic floor, which is usually the same as the house footprint under the roof.
Tips from the field
- Check the net free area printed on the vent you buy. It varies by brand.
- Never mix ridge vents with gable or power vents on the same attic. They short-circuit each other.
What you'll need
Common questions
What is the 1 to 300 rule?
One square foot of net free vent area for every 300 square feet of attic floor, split evenly between intake and exhaust.
Can I mix ridge vents and gable vents?
No. A second exhaust vent can short-circuit the airflow so the ridge vent pulls air from the gable instead of the soffits.
Where is net free area listed?
On the vent's packaging or spec sheet. It varies by brand, so check before you buy.
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Printed from housecalcs.com/tools/roof-vent-calculator