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

https://spencermlsy639.huicopper.com/what-causes-mystery-leaks-on-a-single-ply-roof

Single ply roof guarantees usually cover 15-20 years, but the actual roof can last 25-40 years with proper care. The guarantee mainly covers materials and workmanship, not wear and tear or damage from weather