Single ply roof guarantees often cover 15-20 years, but the actual service life...

https://source-wiki.win/index.php/Why_Do_Some_Single_Ply_Roofs_Fail_in_the_First_10_Years%3F

Single ply roof guarantees often cover 15-20 years, but the actual service life can stretch 25-40 years if well maintained. Think of the guarantee as a promise on material and workmanship, not the full lifespan