Single ply roof guarantees usually cover 15-20 years, focusing on material...

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

Single ply roof guarantees usually cover 15-20 years, focusing on material defects rather than how long the roof will actually last. In reality, with proper care, these roofs can serve 25-40 years