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

https://zoom-wiki.win/index.php/What_Does_a_Bad_Vapour_Control_Layer_Do_to_a_Flat_Roof%3F

Single ply roof guarantees usually cover 15-20 years, but the actual roof can last 25-40 years with the right care. Guarantees focus on materials and installation, not wear and tear or neglect