Topic

Rain falls, and when it does on any roof, all of it rolls down to the edge and accumulates in this small space in a volume equal to the roof area. There is that math again.

But you can see this large volume of water appreciating it when it is diverted away from the barn. This prevents a mud trough along the outside wall, wet spots inside the barn and even barn damage. All barns should have eve troughs with an associated drain pipe that carries the water away from the structure.