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hack of all trades
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Discussion Starter · #1 ·
Just wondering if a spray foamed roof interior can be coupled with other roof sections, in the same home, that also contains vented attic spaces.

So long as the vented spaces are sealed properly, I'd assume it should be okay? Or is it important to stick with one or the other throughout?
 

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hack of all trades
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Discussion Starter · #4 ·
There are 3 gable sections with 12 in 12 pitch and two 4 in 12 shed-type roof sections. The sections that will have normal attic spaces already have ridge vents and I plan to vent the soffits.

The reason I want to use spray foam is that I'm opening to cathedral ceiling in the long gable and adding a small loft. I don't want to have to fur down a lot or lose headroom in the loft to gain full R value + proper ventilation.

The 4 in 12 shed roof section has 2x6 rafters and very little headroom for me to add depth for batt insulation or blown in + venting.

Wondering if it's stupid to consider this hybrid rather than be consistent with a retrofit unvented roof throughout.

Here's a very simple drawing of the basic roof layout.
 

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Sean
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As long as the conditioned attic / cathedral sections are fully separated & insulated from the other areas you should be fine. Be careful that the HO understands that they are going to have to use exhaust fans (and they are vented outside) or you can run into moisture issues esp. in the hot roof areas.

Personally going all open cell in those areas would not be my first choice, but if done properly it can work.
 

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hack of all trades
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Discussion Starter · #6 ·
I think what I should be using is closed cell, but I've heard mixed opinions on open cell w/ vapor barrier vs closed cell. If I had the room to drop the ceiling enough to properly insulate and vent, I would, but I don't have much to work with.

Current roof venting is kind of random and haphazardly installed gable vents with recently added ridge vents (corrugated roll out type that don't seem like they're pulling much).
 

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I think one of the biggest issues here is... how much ventilation space do you leave between the sprayed underside of the roof, and the sheetrock (or whatever) ceiling? I'm not sure how the spray whether it be closed cell or not, will effect the moisture issue.

I would't chance it either. It would be an exensive re-do later.
 

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hack of all trades
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Discussion Starter · #8 ·
KermieB said:
I think one of the biggest issues here is... how much ventilation space do you leave between the sprayed underside of the roof, and the sheetrock (or whatever) ceiling? I'm not sure how the spray whether it be closed cell or not, will effect the moisture issue. I would't chance it either. It would be an exensive re-do later.
If there's no venting, what's does it matter how much space between the drywall and foam insulation?
 

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Pro
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Because closed cell insulations effectiveness does not increase as much as you'd think with greater thickness.

If you can do a pre-vent on the cathedral sections before the spray guys arrive, you will actually extend the life of the roof with an air channel on the underside of the roof sheeting.

You did say there was a ridge vent, no?
 
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