Proper Installation of metal roof

Richard Phillips
10/1/2013
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
Classic Products, Inc.
10/1/2013
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).
Info @windowsonwashington.net
An informed customer is our best customer.
10/2/2013
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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