XPS or polyiso interior rigid foam?
Good day all. I am at decision making time and need your advice. I was brought into a project halfway through (on the new in laws property) and I’m trying to do the best with what I have. The structure is a large BarnPros pole barn with 2200 square foot loft apartment. The exterior of the building was previously completed. Standard cheap construction, osb sheathing under Lowes house-wrap(in some places) with hardiboard siding. The exterior walls are 2×6 and way, way, over-framed. Lots of loss to thermal bridging. I have used R21 fiberglass in the wall cavities and although I’ve done pretty well there are many odd sized cavities where I just can’t fluff the insulation to fill the open face of the cavity perfectly.
My plan is to put 1″ of rigid foam insulation on the inside of the wall and drywall over it. I can’t decided between XPS and Polyiso. The XPS is a little tougher and cheaper. However I’m wondering if the foil faced Polyiso is worth the extra R1.5. I’m thinking if I went with the Polyiso I’d face the reflective side toward the outside and hopefully pick up some R value from the very small voids I previously mentioned. Insulation will be gasketed and sealed with foam/caulk and taped seams.
So what would you all do? XPS or Polyiso?
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Replies
Lance,
Since you are asking this question on a green building site, the answer is easy: choose polyiso, which is much more environmentally friendly than XPS.
XPS is manufactured with a blowing agent that has a high global warming potential. For more information, see "Choosing Rigid Foam."
You might also want to read this article: "Walls With Interior Rigid Foam."
>So what would you all do? XPS or Polyiso?
I'd use reclaimed roofing polyiso, or roofing EPS, which is much cheaper R and much greener than any virgin-stock foam.
XPS is only warranteed to 90% of it's labeled R value, and eventually falls to the R4.2/inch range after several decades, the same as Type-VIII or Type-II roofing EPS.
>"...there are many odd sized cavities where I just can’t fluff the insulation to fill the open face of the cavity perfectly."
You don't need to "fluff" the fiberglass- push it in with whatever pressure it takes to fill the space. At higher density the fiberglass is higher R/inch and far more air retardent than "fluff".