I'm building a 14×16 tiny house and doing a metal roof. It's a slanted/skillion roof and the rafters are running down from the tall end to the lower end on 16" centers with no cross braces. I'm questioning whether I need to add 2x4s in between all of the rafters or not. The OSB won't be a problem because 4' will always break in the middle of a rafter, but I don't think the metal will always break directly on top of the rafters where I need to screw. Is it okay if some of the screws going into the metal just go through the OSB? Will it have adequate holding power? And should I be concerned about leaking? The rubber for the screws should obviously stop leaking but I'm curious if it's normal to do it this way or not.
Thanks.
Best Answer
No, you do not need to screw into solid lumber (joists, stripping,etc.).
You’ll want to follow the manufacturer’s installation instructions, but here is a major metal roofing manufacturer’ installation chart for screws into plywood, OSB board, and 2 x lumber for wind uplift, which is on page 14:
http://pdf.lowes.com/installationguides/716702706866_install.pdf
As you can see, the thinnest material they recommend is 1/2” (7/16”) OSB board at 9” on center up to 24” on center.
Be sure to follow their instructions in order to obtain the warranty.