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

https://victor-wiki.win/index.php/How_Do_Seams_Fail_on_Single_Ply_Roofs_Over_Time%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