Single ply roof guarantees usually last 15-20 years, but the real service life...

https://echo-wiki.win/index.php/How_Do_I_Stop_People_Walking_All_Over_the_Membrane_Roof%3F

Single ply roof guarantees usually last 15-20 years, but the real service life can stretch to 25-40 years if the roof’s looked after properly. These guarantees cover materials and workmanship but don’t always account for wear and tear or poor maintenance