Ridge vents: are they susceptible to snow drifts and driving rain?
My current design incorporates ridge vents with simple gable roofs (both house and garage).
It seemed to be both the aesthetic and performance choice. I will be using standing seam steel roofing, which seems to have a very water tight ridge vent design.
I was recently frazzled by some comments made by a general contractor we know well, saying when he was building house on lake Huron they had to fix a lot of ridge vent houses they built because of snow drifting issues. According to him, snow would accumulate on the roof, and then the wind gust would blow it in the attic, enough to cause moisture issues and mold when the snow melted.
As anyone heard of this before? I will be getting more info on the exact configuration of the problem house (roofing type, make of ridge vent, roof slope etc.) but this was enough to make me second guess my design, given that I am also on a large lake. I could potentially use gable vents, but not only would they be smaller, I am also planning to vent my plumbing through the gable ends, which would make it a bit crowded up there.
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Replies
Mai Tai,
Gable vents are no solution, since wind-blown snow can certainly enter a gable vent.
The short answer to your question is yes, I have heard that wind-blown snow can enter ridge vents. The colder and snowier the climate, and the more exposed the house is to wind, the more likely this problem is.
If the house has a deep layer of cellulose insulation on the attic floor, and a little bit of wind-driven snow lands on top of the cellulose, the snow almost always evaporates (or sublimates) before it causes any problems. Most homeowners don't ever see this type of snow, because they don't inspect their attic in the middle of the winter.
Rarely, wind-driven snow can be a problem. It's very rare for so much snow to enter an attic by this mechanism to cause a stain on your ceiling.
In almost all cases, you don't have to worry. If your house is very exposed to wind, and you are worried, you could design an unvented roof assembly.
For more information on unvented roof assemblies, see these two articles:
How to Build an Insulated Cathedral Ceiling
Creating a Conditioned Attic
Mai Tai,
I have done a lot of work in high-wind areas and yes, vented roofs can definitely take on water and snow through both ridge vents and soffit vents. In those locations I prefer a properly designed and built unvented roof. The rest of the time, for shingled roofs, I always spec Airvent's Shinglevent II ridge vents; they aren't the prettiest but in my experience they are the best at keeping water out. As Martin says, even in low-wind areas, gable vents can take on water and are best avoided.
Mai Tai,
You don't say what type of roofing you are using, but if it's metal most manufacturers sell vent closure strips that will clog before they admit snow.
Here is one example.
https://www.abmartin.net/building-supplies/ventilation/vent-closures
I've heard that a wind deflector can be located near the ridge vent to reduce the air velocity at the ridge vent opening. I'd wait and see if there is actually a problem.
Yes I am using standing seam (snap lock) 26 gauge metal roofing. Specifically, the Heritage roofing product from Ideal roofing. I attached the ridge vent design, which looks good at first glance (2 vertical barriers to keep the water out, they even have a mesh insert which should help with snow).
http://www.idealroofing.ca/english_canada/pdf/accessories/RidgeVent.pdf
Mai Tai,
That looks like a really good design - for insects and rodents too.