Venting flat roof between joists

I've got an old shed that I'm in the process of insulating. The roof is fairly flat and consists of 2x6's running from top to bottom over about 20' with a support beam in the middle. I'm getting ready to install insulation in between each beam and want to allow for some ventilation above the insulation. I was going to just drill some holes at the top and bottom of the roof, actually on the outside walls high enough that it has access to the "cavity" between each set of beams. 1) Will this work? 2) How big should the holes be?
Thanks for any suggestions, Nate Baxley
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Top of roof ?. drilling holes ? how about water leaking in ?
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I blinked at that, too, and then I realized he said "shed" which probably meant a shed roof, and he's talking about drilling holes in the barge-boards and/or under the eaves.
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It's probably not worth the effort for a shed, depending on where you are.
The channel that washes air across the underside of the roof deck should be at least an inch, and better two. The holes at the higher and lower edge should be as big and numerous as you can make them, covered with screen to keep bugs out, and with metal flashing on stand-offs to keep water out.
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