I want to evaluate the retention performance of my green roof design compared to a building with no green roof. I have learned that ecoroof gives outputs such as runoff depth. I have also learned WaterUse: RainCollector using the WaterUse: Storage, collects the rainwater from the roof surface. However, when I run my simulations with and without a green roof, my building "rainwater collector volume" output is the same and doesn't seem to change when I add a green roof. Although, the green roof "runoff depth" output shows a value that is less than site precipitation, which indicates water has been captured by the green roof.
My question is, why do I end up with the same "rainwater collector volume" output when using a building with and without a green roof, while my green roof runoff output indicates there has been reduction in roof runoff?
