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

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

Single ply roof guarantees usually cover 15-20 years, but the actual roof can often last 25-40 years. That’s because guarantees focus on materials and installation issues, not wear and tear over time