RETURN TO I Have An Existing Metal Roof and Have A Question
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It is often a grey area in the code but I very much recommend erring on the side of caution. You can check with your local building officials for their interpretation but that doesn't mean that a future home or insurance inspector will have the same interpretation. If you use battens, the underlayment goes down first. If your existing decking is not nailed to current code, I believe the old shingles have to come off. Also, make sure that the battens are within code and manufacturer recommendation. I am not a huge fan of battens on most applications because they make the roof hard to walk and can cause increased uplift potential for the roof. There are other ways to increase energy efficiency without battens including good attic ventilation or something like an entangled mesh between the underlayment and the new roof panels.
Hello,
I have an 18-year-old shingle roof, and we are looking to have a metal roof installed over the existing one. We've received quotes from contractors, and the plan is to install 26-gauge Galvalume with 1x4 purlins over the shingle roof.
My question is: should there be an underlayment installed over the existing shingle roof? If so, should it be placed above or below the purlins?
We live in Florida, and our current roof had some leaks, which have been temporarily fixed with tar. One area, in particular, has bubbled plywood that will need to be replaced. Will the contractor need to apply two layers of underlayment over this damaged area before laying the purlins?
Reading the Florida building code 8th Edition 2024 from my understanding Roofs requires two layers of underlayment that must be ASTM D8257, ASTM D226 Type II, or ASTM D4869 Type III or IV. Does this apply to metal roofs being installed over an existing shingle roof. I feel like there is a grey area and I want to make sure the job it done properly.
Thank you for your advice!
