cold roof venting: how much vent is enough?
bobww
| Posted in General Questions on
How much vent space makes a cold roof? I am constructing a new roof that should be vented in order to prevent snow melting and ice dams– the idea is to keep the roof deck (this an overroof, new roof deck over rigid foam) at the ambient outdoor temp. This is the only reason to vent. I won’t bother explaining the whole assembly, but suffice it to say that it does not require venting for purposes of moisture management, etc. For various reasons it will save me a fair amount of effort to leave a vent space of only 1/4 inch between the foam insulation and the underside of the sheathing. Is this enough to do the job?
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Replies
> I won’t bother explaining the whole assembly, but suffice it to say that it does not require venting for purposes of moisture management, etc.
I suspect you're not going to get a lot of constructive feedback without details.
bobww,
Once you introduce a vent channel into a roof, for whatever reason, you need to provide a gap deep enough to encourage the air movement you want, to both keep the roof overhead cool, and vent any moisture that accumulates. The minimum depth typicality cited is 1".
Thanks, that's very helpful.
And if the roof slope is low, 1" is not enough.
seabornman,
Good point. Under 3/12, more is definitely better.