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Cor-A-Vent: reduced width?

Phil Boutelle | Posted in Green Building Techniques on

The Cor-A-Vent product is 3″ wide x 48″ long. Do I need the full 3″, or could I rip them in half for 1.5″ vent strips?

This will be installed on top of 1.5″ thick Rockwool Comfortboard 80, with vertical furring strips over the studs.

Any feedback welcome from anyone who has worked with these before. Thanks!

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Replies

  1. Expert Member
    Michael Maines | | #1

    Phil, you can rip them on a tablesaw. I recommend using a high quality acrylic tape to attach them to your furring strips.

  2. Phil Boutelle | | #2

    Thanks Michael. Any other issues with using the smaller strips that you have come across? This is mostly a cost savings measure.

  3. Expert Member
    Michael Maines | | #3

    Phil, I don't have a lot of experience cutting them down but I've done it once or twice. I think they will tend to sag, and may roll. Watch out for staples when you're ripping them. If you want to save money, you might find it less expensive to use metal window screening instead--cut it into 6" strips and wrap it around the bottom of the strapping.

    1. Expert Member
      Malcolm Taylor | | #4

      Micheal,
      Builders here moved away from using screen at the bottom of the cavity because it was too susceptible to mechanical damage - especially weeds or grass growing through it - and once torn can't be replaced.

      We use perforated J-flashing, which is more difficult to clog and better resists pests than Cor-a-vent.
      https://www.menzies-metal.com/vent-flashings/perforated-j-channel-rain-screen-low-back

      1. Expert Member
        Michael Maines | | #5

        Malcolm, you've mentioned that before--good point, and it looks like a good product.

        1. Expert Member
          Malcolm Taylor | | #6

          Here in Coastal BC the lumberyards carry standard 1/2" and 3/4" profiles. They will also bend up wider ones to cover both exterior foam and the furring. Because the furring sits in the flashing it also makes installation easier.

    2. Phil Boutelle | | #7

      Michael, I was thinking that the Cor-A-Vent would be nailed in place through the 1.5" Rockwool, so not much sagging. Maybe I'm missing something on how to install it?

      1. Expert Member
        Michael Maines | | #10

        Phil, that should work. You might find that you want to pre-drill the Cor-A-Vent to reduce bouncing when hand-nailing. Framing gun nails would compress the insulation too much.

  4. Phil Boutelle | | #8

    I was looking at the perforated J-channel as well. One worry I have is flying termites; the Cor-A-Vent looks like it would prevent access, but the J-Channel would allow it. But I like how the j-channel could cover both the furring strips and the Rockwool.
    How would I integrate that with a Stucco weep screed?

    1. Expert Member
      Malcolm Taylor | | #11

      Phil,
      The J flashing is attached to the sheathing and extends out only as far as the back of whatever substrate (cement board?) you are using for the stucco. The weep-screed is installed on the outside of the substrate.

      If you are worried about the size of the holes letting in pests you can get the same profile bent from perforated aluminum soffit material. If they can get through those holes, they can get into your roof too. We have flying termites here in the fall. I'e never seen one get through the J flashing, although sugar ants have no problem.

  5. Andy CD Zone 5 - NW Ohio | | #9

    I get the impulse to rip Coravent in half--I just bought some for my project after scouring the internet for a cheaper product. [But wait... aren't you left with one half that does NOT include the fuzzy insect barrier, then?]

    This product (the 3/4" thick version) cost me $85 for 60 linear feet, and a 60 mile roundtrip to pick it up at the dealer because it's not available online. But I simply couldn't work out an alternative that would be durable, easy to integrate, and actually work--the Coravent checks all those boxes. They're probably exercising well-deserved patent rights, but surely some other importer of plastic do-dads could come up with a competitive system?

  6. Phil Boutelle | | #12

    Thanks All. Andy, I didn't consider that part about the fuzzy insect barrier; somehow I was thinking it was integrated to the plastic.

  7. Brian Pontolilo | | #13

    I've also seen builders use roll-out ridge venting products like Cobra vent, cut to fit between the furring strips for this purpose. It's affordable and easy to cut to fit with a utility knife and seems like a durable material that breaths and would keep insects out of the air channels. I'd be curious to hear thoughts on that approach. If there are reasons why it is not a good idea, that would be good to share here.

    1. Expert Member
      Malcolm Taylor | | #14

      Brian,

      That might work fine. Two things I wonder about though.

      When I have used similar products on roofs, I first staple hardware cloth over the ridge to deter rodents. I wonder how resistant to mice the plastic mesh would be?

      The main source of damage to window screen used to block the cavity, is letting grass or weeds grow up behind the siding, and then pulling them out. Again I wonder how easy it would be to clear the space without damaging the plastic?

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