Single ply roof guarantees usually cover 15-20 years, but the actual roof can...

https://caidenaope074.trexgame.net/what-does-service-life-of-the-building-mean-for-roof-planning

Single ply roof guarantees usually cover 15-20 years, but the actual roof can last 25-40 years with proper care. The guarantee protects against faults, not wear and tear or poor maintenance