new ridge vents blocked with snow - ice dams

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Old 11-23-15, 11:19 AM
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new ridge vents blocked with snow - ice dams

just had my roof replaced. we converted from the standard metal turtle vents to continuous ridge vents. the ridge vent is filtered/baffled and designed for areas that get snow.

1st snow of the year, 12 inches, and the ridge vents are completely covered & blocked. attic ventilation is cut off --- the attic temp is hovering around 38deg when it's been in the teens and low 20s outside. before the snow, and after the new ridge vents were installed, I measured about 5 deg temp rise in the attic (18 outside, 23 in attic). the snow is clearly trapping warm air in the attic. the warm attic is slowly melting the snow and causing ice dams at the eaves.

we never had this problem with the old roof.

questions:
1) is this normal with ridge vents?
2) what can be done about it?
3) should I add a powered attic ventilator (gable end or roof-mount?)
 
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Old 11-23-15, 12:30 PM
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I'd say its normal... its 72F right below the attic for goodness sake... and to get a snow rake. Attics are rarely if EVER below freezing on a sunny day even when the roof is clear. All the snow is insulating the roof in a way, since snow is probably keeping the cold out... and the heat in.
 
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Old 11-23-15, 12:48 PM
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X hit the nail on the head, most of that temp rise is due to the insulation from the snow. With just low vents, the soffits, you will still have lots of air flow from any winds. Granted it is nice to have both high and low, but not a catastrophe if the ridge is blocked for a day or two.

A ridge vent will often melt a way through, or you can help it along with a long roof rake.

This early in the season that one foot of snow will probably melt off. But if it doesn't, then some raking might be needed and yes, snow blocking a ridge vent is normal. I would consider adding gable vents if you want to avoid the blocked vent issue.

Bud
 
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Old 11-23-15, 01:44 PM
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roof rake? yikes, it would have to be about 40 feet long! 2 story house with very high/steep roof.

would insufficient soffit venting cause this? I didn't add more soffit vents. currently theres a vent in every 3rd rafter.
 
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Old 11-23-15, 01:51 PM
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What are the results you're expecting to see? As X and Bud said, this sounds normal.
 
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Old 11-23-15, 02:21 PM
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Maybe a drone with a snow scoop, LOL

Yes, limited soffit venting would slow the air flow, but I've seen many ridge vents covered with snow.

Gable vents would re-establish the expected air flow, plus more soffit venting, but the basic issue of snow covering the roof and insulating it will remain. Passive ventilation is over rated because it is powered by the very heat it is supposed to eliminate. As the attic cools the air flow decreases. Your 38 with low 20's outside is close to what I would expect. Your 5 differential is not achievable through convection alone, I suspect it was wind assisted or a clear day/night when radiant cooling is strong. That blanket of snow is a real blanket.

Bud
 
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Old 11-23-15, 04:00 PM
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would insufficient soffit venting cause this?
I'd say the 12" of snow caused it. I also bet that 12" of snow would have covered up your old vents too. The difference is they might melt open faster because they are METAL which would conduct and radiate heat more than ridge does. Again, perfectly normal. I'd suggest you worry about something that matters.
 
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