Metal roof over asphalt??
I’m about to reroof a 19 year old house with standing seam metal roofing. The current asphalt shingle roof is worn but there are no signs of damaged shingles anywhere and there have been no leaks. One “expert” bidder says I must strip the old shingles off the roof while the other “expert” bidder says there’s no need to do so and it’s common practice to apply metal roofing over a single course of asphalt. It is a BIG roof and there’s about a $10,000 difference in estimates. Anyone have any experience that would be helpful.
With standing seam, it might be a bit of a pain to screw the flanges down to the uneven surface of the asphalt shingles without distorting the standing seam and making snapping the next panel down more troublesome.
I've put on a few standing seam roofs but always on new construction so I'm just kind of mulling over your situation, with nothing but speculation on my part.
I suggest you relocate your post to General Discussion or Construction Techniques and try to get Piffin's attention.