metal over shingle need underlayment or not?

Guest User
12/22/2009
One of my contractor quotes say to lay 29 gage metal roof over shingle he needs to put Titanium Underlayment on shingle first to avoid some chemical reaction the shingle will cause excellarted discolorment on the top side of the metal The other two contractor quotes uning 26 gage say that expense is not necessary.. the two existing layers of shingle and tar parper over the wood serve as underlayment and they never heard of shingles reacting with the back side of the metal causing discolorment of the top side. Who is correct? What is considered best practices for putting metal roof over top of existing shingle roof?
Todd Miller
Isaiah Industries, Inc.
12/25/2009
I have never witnessed the discoloring issue. I do however always suggest new underlayment. Partly to prevent abrasion between the old shingles and the back side of the metal. I also feel that it is required by the international building code.
Guest User
12/29/2009
[email protected] Thank you so very much for your input The guy who suggested the underlayment to avoid exterior discolorization on the outside of the metal was quoting 29 gage while the others who are not recommending the Titanium underlayment are quoting 26 gage Isn't 26 gage considerably thicker than 29 gage? Isn't thicker generally better than thinner? Thanks [email protected] I am also going to try to send this question directly to the e-mail address I saw on your reply if that is ok
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