Single ply roof guarantees often cover 15-20 years, but the roof can last 25-40...

https://wiki-saloon.win/index.php/Incompatible_Adhesives_on_Single_Ply_Roofs_-_What_Happens%3F

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