Somehow you really need a vapor barrier. I do not think insulation alone will be adequate.
If you can create a vented air space, that would be helpful as well.
Todd Miller
2014-01-25 10:02:45.000000
Gentlemen,
I have an existing pole barn that has been enclosed with walls. Also a plywood and shingle roof has been put over the existing sheet metal roof. I am installing 3/4" rigid insulation on the ceiling inside to stop the condensation. My question is this (please see the attached photo).
Would it be better to install the insulation on the bottom of the rafters and create an air gap between the insulation and the underside of the roof or cut the insulation and install it between the rafters, directly to the underside of the metal?
Thanks in advance for your help!
David Dismukes
2014-01-25 09:21:19.000000
If you place the insulation inside the rafters, the rafters will still be a cold spot and have the potential for condensation. I would convert the roof to a vented assembly and if you want to put rigid foam over the underside of the rafters, you need to make sure that the foam has a vapor permeance that will keep the moisture out of that assembly.
That foam will need to be covered with a thermal barrier as well.
Please check local code for compliance.
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