Single ply roof guarantees usually cover 15-20 years, but these roofs can often...

https://blast-wiki.win/index.php/Managed_Decline:_Can_You_Plan_Replacement_Without_an_Emergency%3F

Single ply roof guarantees usually cover 15-20 years, but these roofs can often last 25-40 years if well maintained. The guarantee mainly covers material defects, not wear and tear