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TOPIC: Roofing over existing roof

Metal Over Shingles with Moss, very damp climate

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I have a cabin, located on a riverbank in NW West Virginia, in near total shade. The current asphalt roof needs replaced and I spoke to a local supplier about galvanized roofing materials. I know this is the way to go. MY old roof has at most two layers, but is heavily embedded with moss. What would be the best solution to prep this roof for the new metal roofing. The contractor recommended I lay 1 by furring strips and apply the metal to the strips. He said given the conditions the airflow would help keep things dry. I initially thought I'd have to tear the roof off, but would like to avoid it. I temp roofed a section with roll roofing where moss was not so heavy and simply took it off with a wire brush before rolling the new roof on. I'm hoping I can do this to the main roof as well vs. tearing it off.
Guest User

10/9/2003
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Several things to keep in mind ... 1) I am assuming you have no building code restrictions present which would prevent a third layer of roofing. 2) If you choose to put down purlins and go over that, make sure that the metal roofing panels you choose are approved for that type of application. 3) If that is what you do, I suggest installing vertical purlins first followed by horizontal purlins and the roofing panels. This would allow you to achieve flow trhough-ventilation utilizing a vented eave detail and ridge vent. 4) An appropriate underlayment should be installed over the old shingles first. 5) With proper attic ventilation, you could also consider installation direct over the old shingles -- no purlins at all. Check with the manufacturer of the metal roofing of your choice to see if this could be done with their product. I hope this helps. Email me direct if you have more questions. [email protected] Todd Miller
Todd Miller
Isaiah Industries, Inc.

10/12/2003
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