I am building a 25 x 30 shop with an open 14' lean-to on low side. Single slope Roof an 4/12 pitch. 2 x 6 framed walls with 2 x 8 exposed rafters on 16" centers (span will be 14.5' and 12' approx. with a center beam). I was thinking of running 2 x 4 horizontal purlins leaving 4' between purlins and laying 4' x 8' 1" or 1.5" rigid insulation between purlins and screwing metal roof to the purlins. Will this create condensation issues on the underside of the metal which could eventually rot out the 2 x 4 purlins and cause a problem with the roof fasteners?
David White
2017-04-18 14:18:32.000000
I think a foil-faced insulation is allowed. What is your opinion on the condensation?
David White
2017-04-18 16:48:22.000000
You will need to check code about the foam being exposed to the inside if you are not going to do solid decking.
They may require that you sheet or to require a specific foam that is rated for open exposure.
See that they say and that will somewhat dictate your design requirements.
Eric Novotny
2017-04-18 14:29:58.000000
My concern would be with getting the seam sealed between the sections of foam to make sure that air and moisture aren't getting to the backside of the roof. I would recommend taping those seams and incorporating some underlayment (synthetic polypropylene) to make sure there is no air movement getting up there.
