DIYbanter - View Single Post - Extending R-value for cathedral ceiling

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wrote:
DK wrote:

Here in the southern US, not leaving a place for ventilation will cost
you a roof job about 10 years before it should.

Why would you say that? Seems unlikely to me, if there's no chance of
condensation from moist house air leaking up under the roof.

Nick

Because that's how cathedral ceilings are built base on years of
construction experience. You provide a space between the insulation
and the sheathing so that air can move from soffit to peak, where it
exists via a ridge vent or other venting mechanism. I doubt you;d get
a building inspector to pass off on an unventilated cathederal ceiling.
Besides moisture, what do you think having no air flow under the
sheathing is going to do to the life of the roof when it gets to 150 in
the summer?