Single ply roof guarantees, typically 15-20 years, cover defects but not the...

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

Single ply roof guarantees, typically 15-20 years, cover defects but not the full life the roof can deliver, which often stretches to 25-40 years with good care