TOPIC: I Have An Existing Metal Roof and Have A Question
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I was wanting to know when a new metal roof is installed over an existing shingled roof is there supposed to be an underlayment put downand closure foam used to keep out debris ,insects and rain .
If the metal is installed direct to the deck, rather than up on battens, yes, my understanding of the building code is that there should be a smooth surface underlayment between the old shingles and the metal. This is also just good practice. If the metal is up on battens, I still interpret the code as requiring underlayment. Not everyone interprets it that way though so underlayment is not always used in that case. I personally encourage it though. As far as foam closures, that is up to the type of panel being installed and the method of installation. Yes, on panels that create large voids, there should be some kind of closure at the top under the ridge. Sometimes it is metal, sometimes it is foam. Closures at the bottom are a little more unusual and probably not essential in all cases. Adhere to manufacturer recommendations/specifications.
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