How to vent this attic?

Roofing/Construction Questions
#1

I need some advice. I need to replace the roof over my attic. It’s a bit over 1000 square feet. At the moment, the only ventilation comes from two small gable vents. The roof has no eves or soffits. The attic is poorly insulated, so I also plan to have it air sealed and insulated with blown-in cellulose.

The ventilation is inadequate. I would like the attic to be cooler in summer. In winter there is a risk of ice dams (I live in NY), although I’ve never seen any evidence of them. After some research, it seems I have two ventilation options. Which of these, if any, makes more sense?

  1. Add a ridge vent and an edge vent such as this one. There are a couple of issues with this approach. One is that I have a 45 foot ridge and only one edge. The other side of the house has mostly vaulted ceilings. The diagram found here shows how it’s arranged. That means that a ridge vent with 18 inches NFA/foot will have twice the exhaust venting capacity as the edge vent at 9 inches/foot.

The other problem is that the attic is at most 3.5 or 4 feet tall from the ceiling joists to the ridge pole. Is this enough height difference to get good air movement from the edge intake to the ridge exhaust?

  1. Add a powered roof vent such as QuietCool’s “smart roof mount attic fan”. In this case I’d have to add a significant amount of intake venting as the two gable vents probably don’t add up to anywhere close to the recommended 4 square feet of NFA. I would probably add some turtle vents. The right side of the roof is not visible to anyone so it can be ugly - but I do want to minimize the potential for leakage and ice dams. Does it matter where they go on the roof - up close to the ridge or down by the edge? Or halfway up? Or is there a better intake venting option?

Any advice would be appreciated. Thanks!

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#2

I’d put in insulation and stick with the gable vents. Maybe put a fan in one of if makes you feel better. Whatever you do isn’t going to appreciably cool the attic space in the summer. As long as you are moving the air through to prevent mold, you’re fine. You have a minimal amount of attic space, insulate it adequately then don’t over think it.

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#3

Thanks.

The QuietCool smart fans have an app that lets you monitor the attic temperature and humidity. There are numerous online reviews stating that the temperature goes down after the fan comes on. So I am not sure it’s necessarily the case that a fan won’t cool the attic.

#4

Well you read it online so it must be true.

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#5

You have a situation that can’t be easily or economically addressed.

The best solution would be to install a cold roof.

You likely have blocked intakes that need to be addressed if you are to install the edge type vents.

As it is you can install a fan in one of the gable vents to get the air moving, this would likely work well.

#6

Actually there are no intake vents at all as far as I can tell. I initially thought it would make sense to install edge intake vents and a ridge vent, but I am not sure the height difference is great enough to get good airflow.

The gable vents are very small and probably can’t accommodate a fan. Please see the photos:

The height of the shingles is about 10 or 11 inches, and from that you can guesstimate the area of the gable. I’d say probably no more than 1 square foot of NFA per vent.

In theory the gable vents could be enlarged, but actually each gable is above another roof for the 1st floor. There isn’t a lot of space between the 1st floor roof and the bottom of the existing gable vents. I’d be worried about snow building up and getting in if the gable vents were much lower.

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#8

We are also working towards creating a new vent for one of stay place and I was doing some basic research on this. Had come across this article which had vents listed but what could help you is the small Q&A area when you scroll down the article a bit. That part contains some information which could be useful to you.

#9

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#10

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#11

Thanks. The article does have lots of useful info about ridge vents, but the bigger problem is the intake vents. As far as I can tell, there isn’t enough roof edge to install sufficient intake vents to match the ridge vent if I install the ridge vent along the entire ridge. But maybe it’s not necessary to have the ridge vent extend all the way.

#12

Don’t go t sites like that. They hire writers that have no background, compile any crap they can find online, then puke it out as if it is worthwhile. Roof venting, changing diapers, and what color to paint the kitchen should give you a clue. Ridge vents work sometimes. It’s been below freezing here for 2 weeks. ALL of the roofs without snow, except the eaves, are ridge vented.

#13

So, is it a good thing or a bad thing that the ridge-vented roofs don’t have snow above the eves? I’m guessing a bad thing because it means the roof became warm, snow melted, and now there are ice dams down by the eves. Which would suggest that cool air was not making it up from the soffits to the ridge, and instead warm air leaking into the house was getting up there and melting the snow. Am I on the right track here?

I also took a walk in my neighborhood recently (a few days after we got a big snowstorm). The one house that had even snow cover from edge to ridge was relatively new construction, with cathedral ceilings in at least part of the house. Like many houses here (including mine) there were no eves. I’m guessing the house was insulated below the roof deck really well, probably with spray foam, even in attic areas.

#14

Spray foam causes problems. hot air rises of it’s own accord, called convection. with no escape, it will fill the void, like an oven. your gable vents will let hot air out and cold air in, by stratification. Blind em with brilliance or baffle em with bullshit. The majority of the ventilation game is sales. When I was doing insulation during the “energy crisis” in the 70’s, we’d drive around at dawn and look for roofs with no frost or snow on them. Sales recon!

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