Single ply roof guarantees often cover 15-20 years, but the actual service life...

https://wiki-coast.win/index.php/Overlay_vs_Full_Replacement_for_a_Single_Ply_Roof_-_When_Does_Overlay_Make_Sense%3F

Single ply roof guarantees often cover 15-20 years, but the actual service life can stretch 25-40 years with good care. Guarantees mainly cover manufacturing defects, not wear and tear or maintenance lapses