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

https://wiki-stock.win/index.php/How_Long_Does_a_Single_Ply_Membrane_Roof_Last_in_Real_Life%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