Helpful? 0

Condensation with 1" polyiso rigid insulation..

Looking for some help here..
This past summer I started a 24x36 addition at the cottage.. Its 2x4 construction, sheeted with 7/16 OSB with 1" foil faced Polyiso on the exterior, tapped seams and all.. Its also strapped with 1x4 to accept either board and batten or channel siding at a later date. It is basically shelled with no insulation other then the polyiso on the exterior. My problem is this: After doing more research, I've come to learn that I didn't go thick enough with the polyiso.. I live in Northern Ontario (zone 7 i believe) and at some point plan to heat this cottage during the winter.. Ive scoured the net and found that I probably should have upwards of an R10 on the exterior if I want to avoid condensation during the winter months.. My 1" polyiso is a mere R6.5, or more of a R5.0 during our -20 degree celsius days (which we seem to be having plenty of this winter). So my question is how should I proceed? I do not want to peel all the strapping and remove the windows to add another inch of Polyiso or xps..(windows have a built in brick mould) I was thinking maybe 1inch spray foam inside the wall cavity and go with the flash and fill method? Or maybe my 1" inch of polyiso and standard fiberglass or roxul insulation with vapour barrier will be ok? I see alot of people around here add 1" off rigid foam when installing new siding.. what do you guys think? I want this cottage to last.. I want to do it right.

Asked by Brad Horton
Posted Wed, 01/29/2014 - 17:05


2 Answers

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The best thing is to pull the windows, pull the strapping, add *at least* another inch of foam, and then re-install everything, including the windows on proper pans that drain outboard of the foam. If that's absolutely impossible, then maybe spray-foam the stud bays (I would consider going full) and scrupulously manage the interior humidity in the winter. Personally, I would just go for #1... do it right... get it over with.

Answered by David Meiland
Posted Wed, 01/29/2014 - 18:04

Helpful? 0

thanks for your input Dave..
Seeing how everything is still bare, im leaning towards the spray foam.. I've also seen people fill their wall cavities with closed cell rigid foam.. caulking or foaming the gaps. I believe the term is poor mans spray foam..

Answered by Brad Horton
Posted Wed, 01/29/2014 - 19:14

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