Single ply roof guarantees usually cover 15-20 years, but the real service life...

https://www.slideserve.com/gwyneyxcez/why-do-roof-problems-show-up-after-two-winters

Single ply roof guarantees usually cover 15-20 years, but the real service life often stretches to 25-40 years. That’s because guarantees focus on material faults, not wear from weather or maintenance issues