In the absence of the airtight ceiling, roof ventilation can perform much more damage than excellent, because air movement in rafter bays can encourage indoor air to leak via ceiling cracks.
Like Doug's layout, the main focus is on developing a higher perm layer for drying to the outside, that will nevertheless make it possible for venting though blocking wind washing in the fluffy things.
As for my Vitality auditor recommending blowing cellulose to the mansard sides, you also propose towards that? I used to be beneath the impact blown cellulose stops moisture migration.
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By Martin Holladay
I have developed dense-packed unventilated roof assemblies quite a few instances without the need of issue. Certainly I have not torn into them either. I would want to see much more examples of failures in These types of assemblies when they're to choose from.
Your program to put in 8 inches of rigid foam is a great 1, however , you might be able to install thinner foam when there is a persuasive cause to do so. Certainly, eight inches of rigid foam has a better R-price, and can execute far better, than a thinner layer.
On an unrelated subject: The Chilly Weather Housing Exploration Center has manufactured a online video (below) exhibiting one particular means of making an insulated cathedral ceiling. The strategy demonstrated within the movie is especially appropriate for builders in climates issue to ice dams.
Q. "You say 'You don't want an inside vapor barrier,' but You furthermore may declare that 'you need a superior air barrier on either side of one's fiberglass batts.' The latter would change into an inside vapor barrier not so?"
Martin, go to this website Thanks in your reply. People content articles are both incredibly instructive. I'm getting the feeling that SIPs can be done perfectly, but is often defeat in value with exterior rigid foam techniques as you've proposed, with equal or improved performance (with emphasis on air-tightness).
OK, I had been figuring that the entire of the rigid foam + cellulose had to be a specific R-worth together and were pondering making use of significantly less rigid foam. I have been reading through about distinctive forms of cellulose. Considering that I'm setting up from earlier mentioned would a thing like stabilized cellulose function because it has a little bit water extra?
I'm guessing that neither of these information specifically suits your requirements. But as I noted earlier, if you want a tailor made detail, you probably need to have to rent an architect or an engineer. Fantastic luck.
I was skeptical of Invoice Hulstrunk's claim that AccuVent baffles could stand up to being dense-packed within an enclosed cavity.
It is just a code violation to setup an air-permeable insulation like fiberglass batts in between unvented rafters. It's also a bad idea, due to the fact humidity can accumulate on your roof sheathing if you try this technique, and you may end up getting sheathing rot.