Control flow drains are designed to slow the rate of runoff from roofs during storm events. These drains typically have an insert with a weir that regulates the flow of water through the drain. They are available in a variety of heights. Generally, flat roofs have lower weir heights than sloped roofs. Some models have adjustable weirs which can be set for each drain / location, and some may utilize copper flanges to inhibit root growth. All control flow drain systems should be carefully designed by a licensed professional engineer. These manufacturers sell controlled flow drains: