Single ply roof guarantees often cover 15-20 years, but the real service life...

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

Single ply roof guarantees often cover 15-20 years, but the real service life can stretch 25-40 years if looked after properly. Guarantees focus on materials and workmanship, not wear and tear or how the roof’s used