A downspout adapter simply connects square or rectangular downspout piping to round piping running away from the building, often referred to as a “roof drain leader.” This connection is typically made at or above finished grade. This type of connection requires the use of lightweight downspout running all the way to finished grade and piping next to the building running vertically up to finished grade.
With the exception of gum and duct tape (and we’ve seen both in use), adapters are the lowest-cost connection option. Adapters are also sometimes used in light commercial buildings to form a connection in concrete slabs.