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Attic ventilation to eliminate ice dams

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We own a 1978 Colonial in New England with ice dam issues. I am having a new roof put on this spring and I wanted to increase the venting. Our footprint is 33x22 and a little less then ½ of the attic is a cathedral.

We currently have a ridge vent and soffit vents with proper vents. Our over hang is about 11” and the soffit vent runs the full length of house. I am considering adding vented drip edge to increase air flow and blocking of our one gable end vent, what do you think?

I also plan to remove all the insulation then spray foam all cracks and openings and re-install new insulation. Any suggestion on how to eliminate the ice dams?

asked in Attic Area by brian-coates (120 points)
edited by darekrudy
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1 Answer

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Hi Brian,
 
I don’t think that I can suggest more than what I’ve already said in my “Attic”  category posts. If you know exactly which part of the attic / roof the ice dams are attracted to, start from this particular section of the attic.
 
Drip edge vent is the last resort if there are no soffit vents installed (or no way to install soffit vents) and it is not necessary if your soffit vents are performing properly and providing sufficient amount of air flow. Also, when covered with snow or even little ice, drip edge vent performance may suffer. 
 
I would rather make sure that there’s nothing blocking the existing soffit vent and that what you see on exterior (screens, grills, etc.) is not just for aesthetic reasons; make sure that there is a cutout along the entire length of the soffit vent.
 
Furthermore, calculate the air flow area of top and bottom attic  / roof vents (50% for each would be ideal) and compare with the square footage of your attic – more is better, especially in cold climates like yours - attic ventilation post.
 
One problem with passive roof vents, including the ridge vent, is that they don’t perform well or at all under the snow. Obviously, you’re not going to climb up the roof and remove snow from its ridge. The solution would be to install humidistat controlled power vent which will kick in as soon as the humidity level rises and activates its sensor. 
 
For the cathedral ceiling section check cathedral ceiling ventilation post.
With the soffit / ridge vent configuration you should not have any active gable vents because they disturb air flow between the soffit and the ridge. 
 
Removing the insulation to spray all cracks and openings is a very good idea. You can watch this short video for possible areas to investigate. You could also ensure that there’s a proper vapor retarder installed beneath the insulation.
 
New England is in a climate zone #6 which requires either a Class I or II vapor retarder on the interior side of frame ceiling (i.e., ceiling drywall – vapor retarder – attic insulation), all the vapor retarder type details can be found here - NAIMA 
 
I hope that helps a little, let me know.
answered by darekrudy (21,730 points)
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