Gable vents vs. wind-driven snow: Is there a brand of gable vent known for preventing fine wind-driven snow intrusion?
Another fine snow/strong wind event here in eastern Canada today. After pretty much every storm like this I tend to find piles of snow in clients’ attics, right around the gable end vents on the windward side of the attic (naturally). In one particular case it seemed to be a pretty big factor in the amount of moisture in the attic, as there was serious frost covering most of the roof deck. These gable vents always seem to have the louvers and screens that are meant to prevent rain and snow intrusion, but they fail in this regard when faced with very fine snow being blown sideways. So, to the point: is anyone here aware of a type and/or brand of gable vent known for preventing fine wind-driven snow intrusion?
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You could use Pre-filter material, commonly used to cover snowmobile intakes that are ridden in deep snow. Here's a link to some on Ebay: http://www.ebay.com/itm/like/151577992669?lpid=82&chn=ps
Keep in mind that this material cuts down the amount of air that can come through the opening. Think o f it as VERY fine screen material.
I'd imagine lining the interior with furnace filters would work if the owner could be trusted to periodically clean them.
I've built baffles from aluminum flashing that sit interior to the gable vent and redirect the intruding water and or snow back to the bottom of the vent. One can also lay house wrap material over the insulation under the vent to catch the water or snow. Run it up the gable wall a few inches, and staple the other edges to strapping that sits atop the insulation to make a "pan". Even with 16" overhangs, a strong noreaster will blow through any vent I've seen. I prefer gable vents to ridge vents for this reason. I'm "old-school" and don't trust the baffle material in ridge vents to last 50 years. Perhaps i overdo some of these details, but I also change the screen material on the gable vents to heavy duty stainless screening to keep the attic squirrel- proof.
Kevin, I build almost exclusively on lots with nearby coniferous trees. I've yet to find a ridge vent that didn't quickly get clogged with needles, or allow them through to accumulate on the insulation.
We use furnace filter material. Its worked so far.
Peter,
You've been given some good advice here.
The only point no one has mentioned is that for the past two or three decades, experts have been advising builders that gable vents aren't recommended. In general, a combination of soffit and ridge vents works better than gable vents.
Martin, Isn't the emerging consensus among most of the commentators here that although vented roofs are more forgiving than unvented assemblies, the method and amount of venting isn't as important as air sealing the ceiling. One of the possible sources for damage to the roof assembly is bulk wetting from leaks. leaks that most commonly occur at roof penetrations - and ridge vents constitute the largest penetration by a huge factor. For an unconditioned attic, couldn't it be said that the diminish-ion in efficiency of using gable vents for venting is compensated for by the more robust roof that results?
Malcolm,
In general, you are correct. If you have an (almost) airtight ceiling, there isn't much need for ventilation. The point I was trying to make is that one possible solution to the problem of snow entry through gable vents is to simple block off the vent completely.
For more information on this issue, see All About Attic Venting.
Gable vents are the worst thing you can put in your home in the desert southwest wildfire regions like California, Arizona, Utah, Nevada, Colorado, etc. The problem you are experiencing with snow driving in sideways is the same phenomena that happens with embers from a fire. Both snow and embers are lightweight and sort of "float" around and will easily come into a gable vent. Snow won't burn your house down but hundreds of embers entering your attic gable vent will.
Gable vents are a poor design and a lazy mans approach to attic/roof venting. Gables are also the weakest part of your wall structure when it comes to winds, especially two story gable walls. Typically builders use flat trusses on gable ends and a truss doesn't do well when it comes to supporting horizontal racking loads. Trusses do better on vertical loads from the roof. Martin mentioned better alternatives to gable vents.
Here is a video showing gable vents and how embers flow in like "snow" even though the vent has 1/8 mesh in it. Fast forward to 3:25 to see the gable vent:
https://www.youtube.com/watch?v=_Vh4cQdH26g
Some great advice here, thanks everyone. Will try the furnace filter material as a lower-cost version of the ridge-vent (eg cobra vent) material I've suggested in the past. I'm definitely on board with you Martin on the gable vents not being necessary in an ideal scenario, but there are also many cases that I encounter where it's better than nothing. Unless, of course, they are helping to suck air into the attic from inside the building envelope - but just try explaining that phenomenon to people who are still stuck on the 1/300 rule, and who don't fully understand the importance of air-sealing... been banging my head against that wall for some time now...