Attic Ventilation Installation Reno NV
Reno , NV
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Attic Ventilation Questions and Answers
Attic Ventilation Requirements
What is the proper ratio of ventilation per square foot of roof?
1.5 in per sq. ft. Just make sure that the ventilation is installed so an airway is formed to remove heat through the highest part from the lowest part. Ridge vents and soffit vents work best for this. Also, it is better to have ventilation the entire roof length rather than the 8x12 square vents occasionally in the soffit.
I can't say if it's cost efficient or not, but my attic fan cools the attic a lot. When it's in the 70s outside and the attic fan has not run at all, the attic is too hot to go in. On hot days (80+) it comes on in the early afternoon and runs until about 6:00pm. When it's running I can go into the attic without any problem and it's much cooler.
The ventilation ratios go according to attic floor size not roof size. You can go as low as 1/300 of the attic floor area (for attics which have a continuous vapor barrier below) to a high of 1.5 in inches x the floor area in feet. So a 1000 sq. feet of attic floor area would require between 480 sq. inches to 1500 sq. inches. That is a huge difference in allowance. I would go with the higher number.
One other thing.. the best system uses ridge vents and soffit vents skipping gable end vents entirely. The number would be split about 50-50 between soffits and ridge.