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

https://tessatopmaid.com/approved-contractor-schemes-do-they-actually-matter-for-guarantees/

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