Single ply roof guarantees usually run 15-20 years, but the actual service life...

https://golf-wiki.win/index.php/Why_Is_My_Single_Ply_Roof_Guarantee_Only_15_Years_If_People_Say_40%3F

Single ply roof guarantees usually run 15-20 years, but the actual service life can stretch to 25-40 years if the roof’s looked after properly. The guarantee covers manufacturing flaws, not wear and tear or poor upkeep