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

https://station-wiki.win/index.php/What_Questions_Should_I_Ask_Before_Signing_a_Single_Ply_Roof_Contract%3F

Single ply roof guarantees usually last 15-20 years, but the roof itself can often serve 25-40 years if looked after properly. Guarantees cover specific faults, not general wear and tear over time