Single ply roof guarantees often promise 15-20 years, but the real service life...

https://zulu-wiki.win/index.php/How_Often_Should_a_Commercial_Single_Ply_Roof_Be_Inspected%3F

Single ply roof guarantees often promise 15-20 years, but the real service life can stretch to 25-40 years if looked after properly. These guarantees cover material defects, not wear and tear from weather or poor maintenance