Although it is not a roofing system in itself, the Tapered Roofing Feature is a valuable addition that can be built into any roofing system. It is a valuable addition as it both drains water from the roof and insulates the roof while extending the life span of all roof types.
It's created by laying down a series of tapered sheets of insulation that direct the water to roof drains, scuppers, and gutters. While adding minimal cost to the project, it can dramatically increase the life span of the roof by preventing ponding water.
Duration depends on the roofing system it is combined with.