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Ridge vents being blocked by snow?

JohnBovey | Posted in General Questions on

Hi there.  We’re building in Spokane, WA and we do get some snow.  Usually not a ton, but this last winter (for example), we had about a foot on the roof for about a month.

My question is how much of a concern is it for ridge vents over a cathedral ceiling to get blocked by snow?  It looks like this system (http://www.ventilation-maximum.com/wp-content/uploads/2017/05/CATHEDRAL-INST-METAL-NEW_EXISTING.pdf) would do the trick, but it’s also kind of pricey and might be overkill.

Any thoughts on this matter?

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    Snow is air permeable, and the depths at ridges are small. Even if temporarily restricted by a big dump of maritime sludge snow, it clears in PLENTY of time. At the snow density and depth of Spokane snowfall this is NOT a problem.

    For a building at say 5000' on the western exposure of Mt. Baker it could theoretically be an issue in a high snow year, but even then the ridge vent isn't the greatest concern.

  2. Jon_R | | #2

    I believe that you are in an area with a light enough snow load (< 60 lb/ft2) that, with proper R-value and air sealing, venting is optional for preventing significant ice dams. So don't worry if the vent is sometimes restricted.

    Measurements indicate that snow blocked venting does increase attic temperature, so in heavy snow areas, it's a legitimate concern. An option to solve this is to enclose just below the ridge (a mini-attic) and use gable vents in this.

  3. JohnBovey | | #3

    Thanks for the replies. Just logically thinking about it, it seems like something more arched like this (https://www.lowes.com/pd/Owens-Corning-VentSure-15-in-x-48-in-Black-Plastic-Stick-Roof-Ridge-Vent/3311988) would be better than something more flat like this (https://www.lowes.com/pd/Air-Vent-14-in-x-48-in-Black-Plastic-Stick-Roof-Ridge-Vent/50113110).... right?

    The pictures for both look like they could easily be clogged, but I've never done this before, so I'm not sure. Appreciate any additional thoughts you all have.

    1. Expert Member
      MALCOLM TAYLOR | | #4

      I'm pretty sure those are the same vents. One is just shaped for steeper pitched roofs than the other.

      1. JohnBovey | | #6

        Malcom Taylor: That's what I was thinking at first too, but then in the Q & A section of the more arched one, someone asked, "What is the maximum pitch that this can be used on? It says virtually any pitch. However I have 12's and 16's on my roof & want to make sure it works." The reply from OwensCorning was, "...the VentSure 4-Foot Strip may be installed on roof slopes of 3/12 to 16/12."

        Our roof will be a 4/12, so it seems like it would work, but it might look a bit odd... if you look for that sort of thing. Thoughts?

        1. Expert Member
          MALCOLM TAYLOR | | #8

          You are right they have slightly different openings at the bottom.

          I've used similar ones. The only problem I had with them was they clogged very easily with conifer needles. I prefer this design, although it does mean you can't cover the ridge vent with cap shingles. https://www.pac-clad.com/products/airflow-systems/pac-ss-ridge-vents/

          1. JohnBovey | | #9

            Malcom Taylor: Is that link you provided just for metal roofs? The pics. on that site seem to indicate so.

            Thanks.

          2. Expert Member
            MALCOLM TAYLOR | | #10

            If you look at the diagram below the photo on the link I provided it shows the vent on a shingle roof. How that looks is an open question.

  4. Deleted | | #5

    Deleted

  5. 730d | | #7

    My question is how much of a concern is it for ridge vents over a cathedral ceiling to get blocked by snow?
    Not much, they open fast and vent as designed in short order. In my experience. Unfortunately I have climbed around a a few in the winter.

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