Single ply roof guarantees, typically 15-20 years, cover defects but not the...

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

Single ply roof guarantees, typically 15-20 years, cover defects but not the full life the roof can deliver, which often stretches to 25-40 years with good care