Single ply roof guarantees usually cover 15-20 years, but the actual roof can...

https://oscar-wiki.win/index.php/Do_Certified_Installers_Really_Make_a_Roof_Last_Longer%3F

Single ply roof guarantees usually cover 15-20 years, but the actual roof can last 25-40 years if looked after properly. The guarantee mainly covers manufacturing defects, not wear and tear or damage from poor maintenance