Single ply roof guarantees usually cover 15-20 years, but these roofs often...

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

Single ply roof guarantees usually cover 15-20 years, but these roofs often last 25-40 years in practice. That’s because the guarantee focuses on materials and workmanship, not wear and tear or accidental damage