Single ply roof guarantees often 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 often cover 15-20 years, but the real service life can stretch to 25-40 years if looked after properly. Guarantees focus on materials and workmanship, not wear and tear or maintenance issues