Zip R with flash & batt??
user-6445625
| Posted in General Questions on
Hello
I just came across a project that listed Zip R for sheathing, and then flash & batt in the cavity in a Zone 4A application. I have never come across this combination and was curious how the cc spray would work against the Zip’s foam layer? Good adherence? Does this strategy make sense? My worry would be that the two layers of foam would shear and create gaps over time.
thanks
Brad
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Replies
Brad,
I don't know what the adhesion would be like. What puzzles me is what advantage the cc spray foam gives you over batts or cellulose in the stud bays with the Zip-R?
Spray foam sticks like crazy to pretty much everything. I know for a fact it sticks great to foil faced polyiso, and to "regular" XPS (no facer), so I'm sure it would stick to exposed polyiso too without any trouble.
The bigger question here is "why?" I don't see any reason to do flash and batt here. Tape the seams of the Zip-R the way they tell you to anyway, then seal the perimeter to the framing. Now you have an air barrier -- there is now NO NEED for the supposed "flash" of spray foam to be there for air sealing. Fill the stud bays with batts alone and call it done. If you want some belt and suspenders air barrier details, detail your interior side drywall air tight. Spray foam doesn't really gain you anything here aside from increasing your costs and adding another trade that needs to come through the project.
Bill
In my area, climate zone 6, we need R-11.25 on the exterior of R-20ish in the stud bays to avoid a separate interior vapor retarder other than painted drywall. Unfortunately Zip R-12 is not easy to install properly, so I have seen others use Zip R-6 with a flash coat of closed-cell foam on the interior and either R-13 batts or dense-packed cellulose to make up the difference.
Having three separate insulations on walls seems like overkill to me, but I've done stranger things when necessary.
Thank you all for your responses! Very helpful.
Since the polyiso board used in ZipR sheathing is a closed cell foam - spraying closed cell foam to it adheres very nicely ...
~ formerly worked for a spray foam contractor