A single ply roof guarantee usually covers 15-20 years, but the actual service...

https://web-wiki.win/index.php/Is_a_20-Year_Guarantee_Normal_for_Single_Ply_Roofing%3F

A single ply roof guarantee usually covers 15-20 years, but the actual service life can be 25-40 years with proper care. The guarantee mainly protects against materials or workmanship faults, not wear and tear or accidents