Kory Kitt
I have a double wide with a 3:12 pitch. Some of my decking is starting to rot under my shingles. I was wondering if it would be safe to install a metal roof over 2x4 purlins? What would you use for under layment? Would you put in a radiant air barrier (foil)? Will condensation be a problem? What gauge of metal or type of metal should be used?
Eric Novotny
An informed customer is the Best Customer!
In Nebraska, heating issues shouldn't be a huge issue. If the decking is rotted, I don't like putting good wood over bad wood. In terms of underlayment, any of the synthetic underlayments that are rated for metal are suitable here. Not sure that a radiant barrier has application value in your climate. In terms of metal thickness, many panel manufacturers will use a 26 gauge metal. Some folks that use stiffening ridges can safely run a 29 gauge without any issues.
Kory Kitt
we do get extreme heat and humidity in the summer. Not all of the sheathing is rotted. I think we will make sure the purlins are nailed into the rafters and/or replace some sheathing first. Do you recommend using insulation between the purlins? Do you think condensation could occur in the winter or the summer? Any concerns or ideas I would welcome. thank you
Todd Miller
Isaiah Industries, Inc.
Your greatest risks of condensation are likely during the spring and fall, but, fact is, condensation occurs at dew point and the right (or wrong) conditions can cause it during any season. Insulation can be helpful though generally the bets place for it is on top if the ceilings. If you do add insulation, be sure to leave an air gap, and ventilate that air gap if possible.

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