Can you put 2 layers of felt on a shed roof?
Since roofing felt is cheap, and sheds are small, you can add more than one layer of roofing felt for added protection. Can you double felt a roof? Assuming your roofing contractor is using standard 36" wide 15# roofing felt, "double coverage" means that each layer of felt put down across the roof laps 19" over the upper half of the previous course. (The first course starts with an extra 1/2 wide run).