A client wants to put 1″ polystyrene on his exterior walls. I don’t see any problem with the extra foam, but I was wondering about the order of materials. The studs are 2×6, 16″ o/c, and he will have/wants 7/16″ o.s.b. over the foam board. My question is what is the “normal” protocol for the sequence, and should house wrap be used in an application like this? (foam first then 7/16″ o.s.b., or 7/16″ o.s.b. then foam?). He is using cementatious lap siding for the finish. I was assuming that the foam would go first, then o.s.b. Any problems with an install like this? I sure don’t see any construction of this type in my area. Any thoughts?
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foam first, then the osb...but
you also have to put 1" blocking for all of the trim, because the foam will crush..
AND you will lose the racking resitance of the osb because it is not in contact with the studs..
if this is NEW construction , think about putting the foam on the INSIDE of the wall...
ALSO.. vermin loves polystyrene.. get him to switch to a high density EPS treated with borates and sold under the trade name of Performfuard.. the 1.5 #/cf is pretty strong... the 2.0 #/cf is even stronger...
but hey, whadda i no ?
Mike Smith Rhode Island : Design / Build / Repair / Restore
Thanks for the response(s). If I myself were doing the home, I would consider alternate methods of insulation. Again, it's something I have never seen done around here, and there is some energy efficient construction going on. I've seen the insulated foam panels, sips, etc. I'm not sure the extra $ would be well spent on a detail like 1" foam. I'm thinking he can get a good r-value from the 2X6 cavity, spend some time foam sealing all gaps, etc., and tape his housewrap real well.
Before you cover up any of the walls make sure you know where the studs are. 7/16" OSB will not hold the nails holding the siding. I second using the treated foam.