Proper Installation of metal roof

Richard Phillips
I am having to replace my roof. I currently have a 20 yr old composition roof. It is made up of 30 yr composition over felt. The decking is tongue and groove and is in good shape. I am considering installing a metal roof over the current roof. I have been told that the metal can be installed directly over the old shingles with no underlayment or vapor barrier. What would be the proper way to do this. I am having a contractor do the installation. Thanks for any help you can give me.
Todd Miller
Isaiah Industries, Inc.
As long as you have good attic ventilation, you do not need a vapor barrier. However, I feel that you do need underlayment even for re-roofing. This is to separate between the rough surfaced old shingles and the back of the new metal roof. Also, I feel that it is required by International Building Code (though not all may interpret the IBC that way).
Eric Novotny
An informed customer is the Best Customer!
Is the attic ventilated to begin with or is it an insulated roof deck? Gotta have a slip layer at a minimum and I can't imagine why anyone wouldn't recommend one given the fractional cost.

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