Snow covering roof vents - an issue?

phil17October 10, 2012

So I've read a LOT recently about attic venting and the science of proper eve/soffit vs roof vents, insulation types and quantities, vapor barriers, baffles in vaulted ceilings to ensure air flow, vented vs unvented approaches, etc, etc. But one really basic question I can't seem to find an answer to is... when snow covers roof vents, wouldn't that render them more or less useless? It's not uncommon in many parts of the country (mine included) to get 1-2 feet of snow, which is more than enough to entomb vents such as ridge or turtle vents.

Is there something obvious I'm missing here?

Thanks!

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mike_home

You are correct that snow can block roof vents and make them useless. However the blockage probably does not last long. Warm air is constanlty rising in the attic. Some of it is heat escaping from the house. The other is the sunshine warming up the attic during the day. The warm air melts the snow and allows some air to escape. Watch the amount of snow on your roof compared to what is on the ground. The roof snow will disappear faster.

I don't think you would have a problem even if your vents were blocked for several days. The humidity in the attic would rise, but eventaully it would dry out as the vents become unblocked. If your roof has a peak you could install gable vents to create an alternate airway if the snow is creating a moisture problem in the attic.

    Bookmark   October 10, 2012 at 9:35AM
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fsq4cw

Here in Quebec we have this problem that roof vents would be covered ALL winter by snow.

You're right, it is a problem - a BIG problem!

See the link below for the 100% bulletproof 'Made In Canada' solution.

SR

Here is a link that might be useful: Maximum Ventilation 'Maxi-Vent'

    Bookmark   October 10, 2012 at 10:28AM
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phil17

With all due respect, Mike, humidity/moisture is not the only issue. Even more concerning is the formation of ice dams that cause water to back up under the shingles and cause leaks. If you get a foot of snow, melting enough of it to open the ridge vents is more than enough to cause serious problems.

Thanks for the link, SR - really appreciate it! Looks like basically a mini cupola? I have considered cupolas, as well as dormer vents and gable vents. Problem is, if you have vaulted/cathedral ceilings or a finished attic, none of these solutions will work, unless you install one between every single rafter. For all their controversy, a hot roof (unvented) kinda seems like the only way to go in such a situation?

Seems like this question ought to have been asked/solved a couple million times already. But there seems to be very little discussion about it. Anybody on the ardent "thou shalt always vent" side of the debate care to weigh in?

    Bookmark   October 10, 2012 at 9:54PM
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mike_home

I gave this a little more thought. The ridge vent is at the peak of the roof. I could be wrong, but it would seem a large amount of snow would have difficulty sitting on the peak for long periods of time.

Ice dams usually form where the roof meets the gutter. The melting snow freezes in the gutter and pushes back up against the shingles. Roofers will install a waterproof membrane on the bottom three feet of the roof to protect against this. I don't think you can ever get the attic cold enough to prevent this. I would think a dark colored shingle would absorb enough heat to melt snow.

The maxi-vent looks like a good solution if you live in the snow belt.

    Bookmark   October 10, 2012 at 11:22PM
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phil17

I'm guessing you don't get a lot of snow in your area, Mike? ;-)

Snow can and does often stay on the (entire) roof for weeks or even months at a time.

    Bookmark   October 12, 2012 at 12:50AM
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mike_home

You are correct Phil. In central NJ we sometimes get a few inches for the whole winter. A big snow fall may happen only once or twice in the season.

I can see where a vents can be buried in snow for long periods of time. You guys who get serious amounts of snow have to come up with more creative venting solutions.

I am curious to know if you have observed problems in your attic. What is the slope of your roof? This may also affect the performace of some types of vents.

    Bookmark   October 12, 2012 at 9:51AM
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alan_s_thefirst

Never thought of that shortcoming of ridge vents. I have the old-style whirlybirds, and there's never enough snow to cover them.

    Bookmark   October 16, 2012 at 10:51PM
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