Single ply roof guarantees usually cover 15-20 years, but the actual roof can...

https://mega-wiki.win/index.php/Why_Do_Roof_Problems_Show_Up_After_Two_Winters%3F

Single ply roof guarantees usually cover 15-20 years, but the actual roof can last 25-40 years if looked after properly. Guarantees focus on materials and workmanship, not wear and tear or damage over time