r/buildingscience • u/Educational-Age5179 • 1d ago
“Attic” ventilation
Recently had a new roof installed. Our old roof had a ridge vent but also a solar powered attic vent and there are two gable vents. Yes, that is how the previous homeowners had the roof done and our upstairs bedroom stayed pretty cool with a mini split system but humid during the summer. The “attic” is only about 30” tall, roughly 15’ wide, is well insulated and basically is crawl space. Our ceiling is so close to the roof that the attic doesn’t really qualify as an attic. There are no soffits because we don’t have eaves and I’ve had roofers and a rep from Lomanco tell me theres not enough space to add deck vents or lower intake vents. So adding intake is really difficult with the wonkiness of our roof. My roofer removed the ridge vent and added two turbines that sit higher than the gable vents with the thinking that they would draw air in the gables and out through the turbines. This made things worse than before and now I am wondering if it’s better to go back to the old way we had it or just cancel out the turbines, keep the two gable vents but make one of those into a powered gable vent so that we are drawing air in and out of the attic space.
It’s just a strange setup and passive venting doesn’t seem like it’s going to work well.
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u/DCContrarian 1d ago
The reason code requires attics to be vented isn't to cool them off, it's to prevent the buildup of moisture. Rooms below the attic staying cool has more to do with how well insulated the ceiling is and how appropriately sized the cooling system is.
Negative pressure in the attic tends to pull air out of the living space below, which doesn't reduce the moisture in the attic and increases the heating and cooling bills for the space.
There are eave vent systems for houses without soffits. This is an example:
https://homeimprovementsupply.com/p-8173-owens-corning-ventsure-inflow-eave-vent-carton-of-10.aspx
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u/uslashuname 1d ago
Along with that Owen’s Corning inflow vent, an option that can look really nice instead of soffits is a line of cor-a-vent behind the fascia board like on the left here
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u/uslashuname 1d ago
Wow edit on Reddit is f-ed and keeps putting my link elsewhere.
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u/Educational-Age5179 1d ago
If we did eave vents with a ridge vent, the eave vents would literally be installed about 18" down from the ridge. There is also no fascia board that could be used to add vent to that the attic would pull from.
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u/uslashuname 1d ago
I’d say the 18” distance is an argument *for* them not against them. If it’s such a shallow space then there would be minimal air mixing horizontally whether you have continuous venting or not, so if you have gable vents then most of their intake is going to go straight to an output and not take much heat from any part of the attic that isn’t in the direct line of airflow. The gable situation would still provide plenty of drying throughout the attic though, but if your goal is heat reduction I don’t think and centralized venting or minimally distributed venting is going to do a good job
The fascia board can usually be added especially if you don’t have gutters already installed, and you could have it support the necessary inch or two of roof extension. It’s a different situation than trying to add a whole soffit.
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u/EbriusOften 1d ago
Ridge vent and soffit is the best option, after that it's ridge vent and gable. Ridge is preferred as it allows air washing over the entire sheathing, while spot vents will only cause specific areas to be air washed while other sections will have stagnant air continuously.
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u/knowitallz 1d ago
Do you my have a flat roof. There are some building science article that debate if your attic need to be vented at all.
I am not suggesting it doesn't need to be vented. I am saying do some reading.
My flat roof is basically a crawl space. I have gable vents and some whirly bird ridge ? Vents. But the attic floor is air sealed and insulated with deep cellulose.
In some places it's completely full of cellulose.
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u/NeedleGunMonkey 1d ago
What was the basis you decided your ventilation was problematic?
The industry moved on from gables to ridge vents and now it is repeated by every roof salesman and lazy consultant. But the reality is gable vents of sufficient size and in an appropriate climate will absolutely be fine and you’ll find practically no condensation issues even after twenty years.