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papakevin 03-14-2012 09:42 PM

Metal Roof Install Over Existing Shingles?
I have a small cabin in a camper community and the camp ground handyman is suggesting that I install a metal roof over the existing shingles. The cabin desperately needs a new roof and there are two or three shingle layers on the property currently.

My question: Is it ok to install a metal roof over the existing asphalt shingles? If yes, should some type of underlay material be used between the existing roof and the new metal one? Just making sure this guy does a proper install for me, so any and all suggestions are appreciated.


papakevin 03-14-2012 11:15 PM

2 Attachment(s)
Here are some photos of the cabin so you can see what I'm dealing with. The camper in the back is being removed and the rear roof line extended to enclose in a 10 by 20 room.

oldognewtrick 03-15-2012 04:27 AM

Papa, I see it done all the time. Doesn't make it right. The problem you will have is the shingles continue to deteriorate and will cup and lift the metal compromising the seams of the lap joints. This will also cause the fasteners to start leaking. You create a bigger problem than you have now. If they install batten strips over the shingles then install the metal, you will have the same issues plus you now have a good air space where condensation will become a problem under the metal panels.

If you want to maximize the life span of the metal roof, strip it to the wood decking, use a high temp underlayment like Tamko Metal And Tile, then put the metal on. Several MFg's make high temp underlayments. Don't use underlayments like Weather Watch, they can't take the heat generated by the metal. You can't take shortcuts when it comes to getting quality roofing systems.

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