Single ply roofs often come with 15-20 year guarantees, but their actual...

https://www.booknose.win/single-ply-roof-guarantees-usually-15-20-years-cover-defects-but-don-t-always

Single ply roofs often come with 15-20 year guarantees, but their actual service life can be 25-40 years or more. The guarantee usually covers specific defects, not general wear and tear