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

https://www.4shared.com/office/Q9ZZDzKPge/pdf-27402-44163.html

Single ply roof guarantees usually last 15-20 years, but the actual roof can often go on for 25-40 years with the right care. Guarantees cover faults, not wear and tear or damage from poor maintenance