Interior Zip R ?
I have a 28×28 traditional stick built standalone garage.
It has fiberglass bat r13 insulation on the side walls and R-30 installation across traditional trusses on the ceiling.
Interior is completely faced with exterior building wrap which is permeable and breaths. It’s just traditional box store wrap from Lowe’s.
But it’s all on the inside holding the insulation in the walls. And in the ceiling.
My intention is to use zip r on the interior walls and ceiling not disturbing the exterior vinyl cladding at all. I will simply apply zip r to the interior walls and ceiling and the zip tape on all seams and then I will use a product that is made from real brick but just a brick veneer on the interior from floor to ceiling and the ceiling treatment will be tongue and groove pine painted flat black.
This will give the interior of the space a Brooklyn loft type feel as it has two sliding glass doors side by side on the front of the garage where the garage door used to be and a traditional entry door on the side with a roof extension to create a porch outdoor living area. In addition to windows on each side, the interior will be partitioned with traditional stick framing to create a living room, a bedroom, a walk in pantry, a walk-in closet, and a bathroom.
It’s approximately 750 ft² of floor space on the interior.
My question is does anybody think that placing the zip-R on the interior and letting the insulation and zip-r dry to the outside as a means of keeping the interior walls dry will be a problem?
I’m located in Eastern North Carolina about 50 miles east of Raleigh
There is not continuous exterior sheathing but there is sheathing on about 20% of the exterior walls for sheer loads.
And the exterior is covered in building wrap and vinyl. But at some point I’m going to pull all the vinyl off and install hardie plank siding from 4 ft above ground level to the roof line and below the 4 ft above ground level. It’s going to be a precast rock or stone like sheathing.
Anyway, I’m not using any impermeable vapor barriers but I was just curious as to any thoughts on my use of the products and the way I’m using them.
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Replies
Zip R will work inside as long as the outer sheathing (the wall assembly) is (more) vapor open. A brick look-a-like might not be the best idea because it might trap the moisture in the wall.
Zip-R is fairly vapor open. If your plan is to dry to the outside you want something fairly vapor closed on the inside. I'm thinking a variable permeance product like MemBrain and then either plywood or regular OSB.
DC,
Zip is fairly permeable, but I don't think Zip-R is due to the facing on the foam. Going by the Permeance Chart from one of Martin's blogs, MemBrain goes from less than 1.0 up to 20 when damp. Zip-R is also less than 1.0.
You're right. I read it as regular zip even though I typed Zip R.
DC,
You have probably noticed how many of my posts I have to edit when I re-read the question...
Zip-R's permeance is almost identical to plain Zip sheathing; the fiber-faced polyiso layer is about 1-1.5 perms at 1 inch and the water-resistant coating is vapor-open. That leaves the OSB itself as the lowest-perm component of the assembly, at roughly 0.5 perms when dry and 2 perms when wet. So its performance is comparable to variable-permeance membranes.
Michael,
Martin addressed the confusion in this discussion:
https://www.greenbuildingadvisor.com/question/zip-or-zip-r
I thought regular Zip was more permeable too.
Malcolm, I got my info from the technical directors at Huber and Atlas, who supplies the polyiso for Zip-R. My memory was a little off; the OSB is 0.8-1.0 perms dry cup/1.5 perms wet cup.
Michael,
The difference between the two is in the weeds. Perhaps oddly, our building codes defines a vapour-barrier as being anything under 1 perm.
LaborTank,
My only reservation is over how well the exterior walls keep out bulk water. Adding the interior foam, means less heat makes its way into the walls to dry out any moisture that gets in.
OK, now that I've re-read and realize that it's Zip-R, I have a question: does Zip-R have the shear strength to support brick veneer?
You can install thin brick veneer over Zip R on the outside, so I can't see why it wouldn't work on the inside. Bonus, on the inside you don't have to worry about liquid water and solar vapor drive.
For the OP. I think your idea will work well.