This small building has a footprint of 10' x 12' with a gable roof (sideways, so the gables are 10' apart). Slope is 4:12, so the peak is only 2' above the walls. My ridge isn't vented, so I'll be using gable venting.
The building is cabin-like, so the ceiling will have drywall, a vapor barrier, and insulation. There will be plenty of water vapor to deal with, and the interior will have its own ventilation. Our climate is very mild (snow dams and summer cooling are rarely a problem), but humidity is high most of the year.
I know it's common to vent at eaves/soffits, but they're easier to construct if I skip venting there. Since my roof is only 10' long, I think the middle of the attic will still get enough airflow with only gable-end vents. Is that correct?
I've read that the basic rule for sizing screened ventilation is attic area / 150, but area / 100 if it's louvered, too. If I only do gable-end venting, then I put 1/2 of that at each end, correct?
Any other tips?
Best Answer
Venting should be 1/300 of insulated ceiling area, distributed uniformly on opposite sides of the building. (1/150 if slope is less than 1 in 6)
So whether you go with your 1/150 number mentioned in your question, or 1/300: using any vent larger than 8" x 8" at each gable end you are already going well above and beyond either requirement, so like sherlock homes mentioned in his comment, don't overthink it.
If you use a 12" round or octagon louvered vent at each end you will be safely above 1/300, 1/150, and 1/100.