Climate 3b unvented cathedral roof insulation (a-frame house) Open cell or closed cell is it a tossup?
donarntz
| Posted in Energy Efficiency and Durability on
As the title says, open cell or closed cell unvented cathedral ceiling zone 3b? I’m awful close to zone 4 in Athens, GA. Is it a toss up and if so which. I know open cell is going to be a bit cheaper (but not by much) at 10-11″ vs closed cell at 5″. Standing seam roof so not much drying to the outside. This article says 5″ of closed cell will still dry to the inside in the summer:
https://www.buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates
Is that true?
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Replies
Are you renovating or building new?
1. Building new and possibly for a renovation
Here is a GBA article on how to build vented and unvented cathedral roofs.
https://www.greenbuildingadvisor.com/article/five-cathedral-ceilings-that-work
2. This article talks about the risks of open cell spray foam.
https://www.greenbuildingadvisor.com/article/does-open-cell-spray-foam-really-rot-roofs
I would never ever use the open cell on a roof, even if some might say it is ok in a all year hot dry climate. The article has links to other articles on the same subject.
Closed cell is always safer in unvented roof assemblies. That's what I would use here. Drying isn't usually an issue with these assemblies in practice, even though conventional wisdom is to try to allow drying in at least one direction.
Bill