Difussion Vent for Wide Ridge BEAM?
OK, I have an odd diffusion vent / unvented cathedral question.
My location in the new 2021 IECC map has Reclassified me to the 3C – Warm Marine zone here in Warren County North Carolina (See image). In the 2016 map we were a 4C – Mixed Marine.
So here’s my cathedral roof diffusion question.
My framer forgot to “raise” the rafters a full inch on my triple LVL Ridge Beam… As a result, I’m too wide to use a Vented Ridge Vent for the rafter bays ( I would have to cut vent slits at the very outside edge of the ridge vent. So I’m now planning to treat the cathedral as UNVENTED since I don’t have a convenient way to vent this cathedral ceiling.
I have a small concern about potential rot at the top of the ridge beam that wont be insulated. Since I’m in Zone 3C do I need to even concern myself with the uninsulated air space that sits above the wide LVL ridge beam? I’m thinking a vent that acts to ONLY help ventilate this small uninsulated space sitting above the triple LVL is either OVER KILL, or a nice “insurance policy” against future rot.
PS: The zone label on the image is incorrect… I am in 3C-Warm Marine, NOT 3A.
Thoughts?
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Replies
bradesp,
My suggestion would be to over-frame a slightly larger ridge vent. That way you can still have vented roof assembly.
Another option would be to see if a structural engineer would allow you to rip the corners of the beam off. Doing so would affect the beam's strength and stiffness, of course, but it might be oversized enough to handle the change.
If you do end up spray foaming the roof, in a heating-dominated climate I would be concerned about the space above the beam, because the stack effect would direct heat and moisture to that location. But with your climate it's probably not as large a risk, as long as everything is sealed so it's airtight.
I should add, I'm without carpenters for at least a month, and my roofer arrives Wednesday... So wondering if the ridge vent idea has merit, or if I should roll the nice and not stress over the small area of trapped air between top of the roof deck and the top of the LVL Beam.
bradesp,
I wouldn't worry that much about the beam. It's more whether you want to change your whole roof insulating strategy based on a small fixable problem.