Do I need to remove the single layer of old shingles before putting on new metal roofing?

Why? Why not? What are the Pros and Cons?Do I need to remove the single layer of old shingles before putting on new metal roofing?
This is a personal choice. Most carpenters will tell you to take off the old shingles - I agree. I do not like leaving old brittle shingles under either a new metal or another shingled roof. To me it's like putting on a new shirt over a dirty T shirt. I don't think there is much technical disadvantage leaving the old shingles on, except that those old shingles might crack and break off as workers walk on it to install the new metal roof, but the metal is strong enough that it won't buckle or pucker when they screw it down through the old shingles.


Make sure the roofers install a new metal edge that comes down over the old roof edge that is now on the roof, or take it off.


Ask how they will install the valleys, and flash around any vent pipes,chimney,and other roof penetrations. These are areas that need discussed before they start. Lots of people claim to know how to properly install a metal roof, some of them do know how. The others are fine if it's just a single slope roof with no valleys or roof penetrations, but they really don't know how to do these areas and it looks terrible and they will leak forever.


Don't forget to ask about roof vents? Don't let them roof over them if you have them now. They are harder to install and flash in a metal roof, so they might try to tell you that you don't really need them.


Also ask if there will be any splices in your metal roof panels? Try to avoid these.


Ask questions and don't pay very much money up front. Get it all in writing including a labor warranty covering any leaks. Only pay them after you get a good heavy rain to test out the installation. You can hold back 10% of the total price until you get a good rain to test it out.Do I need to remove the single layer of old shingles before putting on new metal roofing?
I would strongly suggest speaking to some experts first- a roof is the last thing you want to mess with. If you're looking for some good people, I suggest Sela Roofing %26amp; Remodeling, Inc.