Single ply roof guarantees, usually 15-20 years, cover workmanship and material...

https://wiki-quicky.win/index.php/What_Would_Stop_a_Single_Ply_Roof_Reaching_35_Years%3F

Single ply roof guarantees, usually 15-20 years, cover workmanship and material faults but don’t always reflect the roof’s full life, which can stretch 25-40 years with good care