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

https://riveraeku966.almoheet-travel.com/how-do-i-explain-to-my-boss-why-a-15-year-guarantee-is-not-the-lifespan

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