Can You Put New Roof on Top of Old One?

shw001October 3, 2011

Is it OK to put a membrane roof (EPDM, TPO, or PVC) over an existing old flat metal roof (tin). The roof is flat (pitch 1/8 inch per foot). I have a bid from a contractor who recommends leaving old metal roof in place and covering it with a membrane. He would use rigid insulation and/or some type of sheathing board as a separator. Is this installation OK?

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Yes, according to the EPDM Roofing Association.

    Bookmark   October 3, 2011 at 7:35PM
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Too quick on the "post" button. Roofing over is acceptable, but the pitch still remains a problem.

    Bookmark   October 3, 2011 at 7:37PM
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shw001

The pitch is only 1/8 inch per foot, which is OK for PVC, but I am not sure about EPDM. One roofer recommended roofing over (with a separator of either rigid insulation or sheathing). Another contractor said the manufacturers would not warantee material in a roof over. (I think there are more opinions than there are contractors).

    Bookmark   October 4, 2011 at 10:42PM
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One roofer recommended roofing over (with a separator of either rigid insulation or sheathing)

Yes, it can be done. And the slope can beincreased by tapering the insulation.

Another contractor said the manufacturers would not warantee material in a roof over.

Though the trade association of EPDM manufacturers specifically says it's okay....

Instead of taking any contractor's word as gospel, Google up the manufacturer's tech information or give their technical department a toll-free call.

    Bookmark   October 4, 2011 at 11:25PM
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