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

https://wiki-triod.win/index.php/How_Do_I_Explain_to_My_Boss_Why_a_15-Year_Guarantee_Is_Not_the_Lifespan_of_Our_Roof%3F

Single ply roof guarantees usually last 15-20 years, but the actual roof can often go on for 25-40 years with the right care. The guarantee covers materials and workmanship but not wear and tear or damage from neglect