Single ply roof guarantees usually last 15-20 years, but the real service life...

https://smart-wiki.win/index.php/What_Maintenance_Records_Should_I_Keep_for_a_Commercial_Roof%3F

Single ply roof guarantees usually last 15-20 years, but the real service life can be 25-40 years when properly looked after. Guarantees cover materials and workmanship but don’t account for weather or wear