What sheathing under a metal roof?
Jane Metzger
| Posted in General Questions on
We are building a garage. The roof is a 12/12 pitch. We would like to put spray foam insulation under the roof when we have the funds. We have a thermos roof on our house and love it. We thought we were going to use 3/4 inch T&G OSB for sheathing. We then heard complaints about screws stripping out. We really don’t want purlins because we live in an area that can have a lot of hail damage. Should we switch to the more expensive plywood? I feel like we are going around in circles…….
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Replies
Jane,
Most builders would agree that 3/4-inch OSB is a perfectly adequate roof sheathing for a garage. I have never heard that 3/4-inch OSB doesn't hold screws well enough for this application. But then again, I always like to install metal roofing on purlins.
My guess is that you are over-worrying about hail damage. Maybe all you need to do is check your insurance policy to make sure that it covers hail damage to roofs.
Well, it is my husband that is over-worrying. He is an over-builder, too. Eventually there will be a 560 square foot living above the garage. We are installing the floor, but will leave it unfinished for now. That is why I am concerned about the insulation. We want to use the spray foam. I guess calling both a spray foam dealer and the metal roof dealer may answer those questions, but it is nice to hear from other people that have experience.
I will check the insurance policy.
Jane,
Here is a link to a document (sorry for the poor quality of the scan) that appears to show that smooth-shank nails and ring-shank nails in OSB have a slightly higher fastener withdrawal load than the same nails in plywood.
Another source reports an opposite finding: "Tests comparing pull-through strength between plywood and OSB indicate that 17 pounds of force are required to pull out a nail from plywood, but 15 pounds of force from OSB."
In any case, the performance of OSB and plywood in this regard appears to be close.