Single ply roof guarantees usually last 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 last 15-20 years, but the real service life can be 25-40 years when properly looked after. Guarantees cover materials and workmanship but don’t account for weather or wear