This is done rather frequently. I would offset the side laps of the new roof from those of the existing roof. If it has end laps, I would offset those as well. At the eave, I would cut the existing roof overhang back so it does not extend beyond the outside face of the wall. Then I would seal between the new roof and existing roof at this location. If the existing roof has rust spots, I would seperate them from the new roof with some type of material. Possibly a thin insulating material like Solar Guard. You won"t get much R value from it but it will seperate the rusty areas from the bottom of the new roof panels. I'm sure you can find other materials that would work as well or better.
Ken Buchinger
2011-06-23 07:12:57.000000
I have a 26 guage metal pbr roof.
I found a PBR profile that will fit almost exactly over the existing PBR panel.
Due to rainy and safety issues I would prefer to keep the old roof on.
I know the existing screws will have to be removed.
I had a structural engineer "ok" the added dead loads of installing another layer of 26 guage over existing.
What are some negative items that I should be concerned with ?
Have you heard of other people doing this?
mark massey
2011-06-22 23:38:51.000000
thank you for the response Ken and Washington.net
The existing roof is painted white. I was thinking of spraying a type of rust inhibitor where needed. Due to budget reason, I dont think I can use solar Guard. Is there another material that could be used as a "separator" that is less expensive?
mark massey
2011-06-24 08:03:43.000000
A slip layer or spacer layer is a very good idea.
We don't see much of that here but that possible if done right.
If you use the Solar Guard, don't over torque the fasteners.
Eric Novotny
2011-06-23 09:44:23.000000
Any of the synthetic underlayments are fine as well.
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