Recycled polyiso – inside or outside?
I’ve been reading the comments on the best location for the polyiso and it seems to be a six of one half dozen of the other type thing with many of the blog posts 5+ years old.
I’m renovating a 1600 sqft ranch house in Central NY, near Rochester, which is zone 5. I’ve pretty much gutted the interior to the four outside walls and with the number of windows and doors that are being relocated, will end up re-sheathing about 1/2 of the house. Most of the exterior walls will be 2X6 and a small amount of the current fiberglas R19 insulation may be retained.
What are current thoughts on placing the polyiso on the inside of the house or outside of the house? For those who have done it, any regrets or lessons learned with your installation?
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If all of your siding is coming off anyway, installing the polyiso (PIC) on the exterior is preferable for a couple of reasons. First off, this will keep your sheathing warm and eliminate thermal bridging. Second, it is much simpler to install as you do not need to cut and fit strips between studs. If you salvaged the fg batts, I would just stick those back in the stud bays when you are done. When you are resheathing, make sure you know what your air barrier plane is because taping your sheathing seams is a popular solution. You can fit PIC between studs, especially if it is paper faced (foil faced is a vapor barrier), but it is a lot more labor and doesn't address the thermal bridging of studs without adding an additional stud layer of some kind. We are currently doing a double stud wall with paper faced PIC insulation because the building's footprint couldn't increase due to lot size and tight alleys.
I assume you are discussing continuous insulation vs filling bays.
The only reason I see to put the foam on the inside is if you can’t put thick enough foam on the exterior to control the dew point. Otherwise putting it on the outside gives all the advantages of keeping the sheathing and framing warm.
+1 for putting the polyiso on the exterior.
I would avoid doing “cut and cobble”, putting polyiso between studs. If you want a bit more performance from insulation in the stud cavities, use mineral wool here or special order higher density fiberglass batts. Polyiso is best used as continuous insulation.
Bill