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We are in the process of getting estimates for a metal roof (26 guage) over shingles installation with exposed fasteners. We have one company whose estimate will be based of installation directly through the shingles to roof decking without underlay or battens. Is this consistent with best practices or have risks associated with it?
We are located in North Florida and have been advised by four roofing companies that we have between 5 to 7 years of life left in our shingles and no issues with plywood decking.
Diane, It is important for you to follow local building code. While I am not generally a fan of "battens" in this type of installation, I would encourage underlayment and feel it is required by many building codes even if the old shingles are left in place. Also, what you have outlined will drop the roof deck temperature and this could make your attic more prone to condensation unless you have good attic ventilation.
Thank you Todd! Without underlayment would there be any risk of the few roof nails pops we have or even the shingle grit damaging the underside of metal? Would this result in corrosion down the road? Based on what I've read, I'm guessing the underlayment is metal manufacturer recommended...
Diane, the things you mentioned are indeed some of the concerns that I think lead most of us to recommending underlayment.
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