Torch-On roofs typically get less moss growth but can see more algae staining and debris build-up. The debris tends to clog drainage systems, preventing water from properly draining from the roof. Due to their simplicity (they usually have little to no slope), this type of roof is arguably the easiest to maintain. However, if left without being cleaned off for long periods of time, debris such as leaves, dirt, and twigs, can cause problems and in some more severe cases, leaks.