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

https://sierra-wiki.win/index.php/What_Does_a_Manufacturer_Design_Service_Usually_Include_for_Single_Ply_Roofing%3F

Single ply roof guarantees usually cover 15-20 years, but the actual roof can last 25-40 years with proper care. The guarantee mainly covers materials and workmanship, not wear and tear or damage from weather