Cathedral ceiling R-value boost
user-901114
| Posted in General Questions on
Zone 6. Layers from the outside in:
Galvalume steel roof
Grace advantec
Plywood deck
1 inch air space
1 inch foil faced tuff r
5.5 inch roxul
Rafters are filled at 7.5 inches.. 24oc
Question; what can I put under the roxul and rafters to get r38?
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Replies
I would recommend that you install a layer of rigid foam.
What kind would you recommended? Xps?what are the pros and cons of this assembly? Thanks.
Stephen,
The pros and cons of the assembly? You're going to end up with a "foam sandwich," which is not ideal. It's usually better if the foam is only on one side of the assembly, not both. But in this case, you'll probably be alright.
I would recommend foil-faced polyiso -- as much as you need to get the required R-value. Tape the seams with a high-quality tape, and install strapping. The foil facing plus the air space give you a slight boost in your R-value.