Attic Ventilation

Recently inspected an attic with ridge, soffit and gable vents. The gable vents were partly open. Someone had cut a few holes in the osb during construction. My question: Should the gable vents be opened or left closed? Seems I read (and can’t find it now) that the gable vents will interfere with the air flow of soffit to ridge. Any thoughts?

I feel that with fully open and functioning ridge and soffit vents that the gable vents should be closed. BUT…the key is are the ridge and soffit actually installed and working properly. I am careful about telling a client to close a gable vent is there are no signs of any ventilation related issues…no premature thermal deterioration of the shingles, no evidence of ice formation, no visible signs of trapped moisture. If all looks good is it really necessary to close off a partial gable vent? I guess the answer is “home” specific…what did you see is really the key.

The gable vent is mostly closed. My original thought was that it should be opened. House is only about 7 years old. No signs of shingle issues or attic issues. No moisture issues.
But I have read since that a gable vent can be the source of air for the ridge vent, hindering airflow from the soffit. The inspection was over 6 months ago and the owner is just now making the few repairs.

has anyone ever scientifically documented an over ventilated attic?

“short circuit” is a theory that doesn’t have enough supporting data for me to recommend/report anything other than the amount & type of ventilation present and apparent function

With that said and assuming the soffit and ridge are functioning I would make no recommendation regarding the gable vent as it is only partially open. I see no reason to open the gable vent. Just my thoughts.

It isn’t broke why fix it.

What was the configuration of the roof… ie intersecting roof planes creating a dead air pocket… that the few cut holes may have been added to create circulation in those areas that the soffits are not ventilating enough?

Good call. There are some different planes. However, knowing the contractor that originally built the house, I doubt those steps were taken. Original owner has not had any work performed.

Thanks for the thoughts!

Personally I think the more venting the better, but the catch is that it has to be somewhat balanced between ridge and soffit. My local codes wants a 50/50 split of the NFVA between ridge and soffit, but allows for up to 25/75.

If the soffits are wide open I don’t think ridge + gable vent is going to hurt. I wouldn’t bother with both if it was new construction but I also wouldn’t remove the gable on existing.

There have been a couple roof replacement projects I’ve worked on where the attic is large enough that a typical ridge vent cannot provide enough venting, so we added additional square vents near the peak to balance everything out.