Single ply roof guarantees often cover 15-20 years, but the actual 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 actual service life can stretch to 25-40 years with proper care. Guarantees mainly cover material faults, not wear and tear or accidental damage