Single ply roof guarantees usually cover 15-20 years, focusing on material...

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

Single ply roof guarantees usually cover 15-20 years, focusing on material defects rather than how long the roof will actually last. In reality, with proper care, these roofs can serve 25-40 years