Using polyisocyanurate insulation on the exterior of a home
I just read one of the discussions’ on the use of polyisocyanurate insulation on the exterior of a home and how it acts as a vapor barrier and not to use it because it doesn't breath, thus resulting in potential condensation and mold problems within the walls. My concern is that I am currently getting ready to reside my house and I have already installed this on 50% of my home. I wanted to only add 1.5" thick foam to work with my 8" windows jams that I have upgraded to So I wanted the most R value possible from a foam. And polyiso gave this and It was also cheaper then the 2" XPS. I live in Northern Alberta Canada, Zone 5 I believe. My home wall consists of 1/2 drywall, poly vapor barrier, 2X6 walls with Roxul R22, 7/16" OSB sheeting then the 1.5" polyiso with tuck taped seems and then a layer of Typar over top. I have not sealed the bottom or top with caulking or tape between the OSB sheeting and the polyiso so won't this allow any water vapor or condensation to escape, Also I herd the tuck tape will loose its adhesion ability over time so will this save me.
I’m thinking that for the rest of the house I should ditch the polyiso and just add 1.5" rigid XPS to allow for the walls to breath. However I don’t want the polyiso I purchased to go to waste so I was also thinking of just using the polyiso with the XPS, Placing one side by side on the walls. Will this allow the wall the breath enough so that I can do this? Or would I be able to just get away with continuing to use the polyiso and just leave the joints un-taped and leave the bottom and top to vent and drain.
PS: No rush but if someone could reply ASAP that would be great. I am planning to finish the rest of the house this week.
Posted Jul 3, 2011 3:20 AM ET
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