Metal Roof over existing Low Slope Built up Roof

Richard Penn
3/21/2017
I am interested in a metal roof for an old commercial building. The existing roof is a built-up roof and has a 1/12 pitch, parapet wall on front and both sides. The building space is not climate controlled, and there is no attic space....no ceiling between building space and existing roof. There are 2 vents high on the back wall of the building and 1 vent high on each side wall toward the front of the building. My local supplier has a PBR panel than is suitable for this roof pitch and I would like to install this over the existing roof without removing it. Based on other reading on this site, I would apply 30# felt underlayment, then install 2x4's battens running vertically, then horizontal battens on top of the verticals to provide an airspace. Since this is a low slope roof, are there any concerns for condensation on the bottom side of the metal roofing that could cause damage? Any recommendations on venting or insulating?
Eric Novotny
An informed customer is the Best Customer!
3/22/2017
Depending on the climate, some radiant barrier would be helpful here as well. There isn't likely any moisture coming from through the roof and any condensation would be confined to just normal condensation from what moisture might be in the air some overnight lows. The outside surface would be the more likely condensing surface at that point.
Dick Bus
3/22/2017
I do not recommend a PBR panel on a 1/12 pitch. I would recommend a mechanically, concealed fastened panel. A high temperature, synthetic underlayment should be used in lieu of 30# felt. thanks for using a metal roof.
Richard Penn
3/24/2017
Thanks for the help guys! I questioned the application of PBR panel for this roof pitch, but manufacturer states it is acceptable down to 1/2:12 pitch. I will investigate the standing seam.

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