Ridge and gable vents for unconditioned attic
woobagoobaa
| Posted in Building Code Questions on
Re-roof of well sealed unconditioned attic is calling for ridge vent install. Currently this attic has gable vents. Soffit vents are not an option, eaves trim detail is in the way. Roofer is saying we can’t have both ridge and gable vents, close the gable vents or we will fail inspection. Without soffit or gable vents, where is the intake source for the ridge vent?
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Replies
Hi Wooba.
I guess it is moot if you can't pass inspection, but it is fine to have gable and ridge vents. And there options for intakes low on the roof where it is not possible to locate them in the soffit. Keep in mind that one of the keys to letting attic venting work is an airtight ceiling. These articles may be helpful:
Should I Close Off My Gable Vents?
Venting a Tricky Old Roof
A Vent for Every Roof
Venting A Tricky Old Roof ... just the reference I needed. Just FYI the third link is dead. Thank you
Sorry about that. It should work now.
I'm curious if there is any code basis for this alleged "fail inspection". It's not in the IRC.
If it's easy to access the attic, you might seal up the gable vents per your roofer's uninformed opinion, but do it in a way that can easily be removed when he leaves.
Gable vents typically wouldn't give you enough net free air required for a house, that is where ridge vent and pot vents come into play, but it would still be high side ventilation and count towards your upper requirement in WI code.
I do not know IRC requirements, but they will probably be total ventilation “net free area” per x amount of conditioned ceiling, then a provision of different high and low allocations that dictate 1/150 or 1/300 ratios. (1/150 = 1 square foot net free area for every 150 square feet of conditioned ceiling), at least 50% of the net free area is to be provided to the high side, again this is WI state code. 50-75% of total ventilation to high side can use the 1/300 ratio.
As someone said they make low side ventilation products that are on the roof deck side to give you some intake that you roof in. Don't overthink it, but no rational reason to close off gables, and if they do you've still got the ridge venting.
There's this article by Joe Lstiburek. See rule #3.
https://www.greenbuildingadvisor.com/article/lstibureks-rules-for-venting-roofs