Single ply roofs often come with 15-20 year guarantees, but they can last 25-40...

https://andreocln282.lucialpiazzale.com/pvc-single-ply-roof-lifespan-is-30-years-realistic

Single ply roofs often come with 15-20 year guarantees, but they can last 25-40 years in real life. The guarantee covers basic defects early on, not wear and tear over decades