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TOPIC: Rust

New metal roof over old metal

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My old metal roof is probabley 70 years old. Its very rusted on the edges and in many spots throughout the roof. The main reason for replacing it is that I've put on a new additiion, plus when I bought the house it had four shed roofs on it that are covered in asphalt shingles. So I want to cover the entire house in the same kind of roof. My question is can I put down the new metal directly over the old metal (it is very flat without any types of ridges),by using felt paper between them and then screwing it into the existing purlins under the old roof , or shoud I go ahead and put down new purlins over the old roof. If I need new purlins, should they be 2 x 4's or can I use 1 x 3's.
Guest User

11/11/2002
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It is good to see that your old metal roof is still servicing you well however it is finally time to move on. Your existing roof will serve well covered up however condensation from the underside of the new roof may be a problem with the rusty surface and direct contact with the new metal I would recommend a felt paper to stop the condensation on the old metal and minimum 1" strapping over the existing purlins to break the bond however I would ventilate the air space with a vented closure. This will help ensure positive fastening of the new roof as well. Good Luck.
Allan Reid
Dura-Loc Roofing Systems, Inc.

11/11/2002
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Or copy this URL: https://www.metalroofing.com/spirit/comment/1391/find/
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