Sometimes we purposely direct the water towards the inside. Hopefully, all of that water goes into a drain and then a leader (pipe), which keeps the water out of the interior elements. But when one considers that all of the water from the contributing roof area must pass over and through this drain, it often is not given the careful consideration it deserves. I hope to provide you with some specific code requirements and some observations that apply to interior drains, both primary and secondary. I will also cover some other types of drains like scuppers, porch tubes and flashings at the roof edge.
Properly performing roof drainage systems are a collaboration between the designer, the plumbing contractor (if drains are involved) and the roofing contractor. However, after the initial design and installation, most types of roof drainage, except for some of the plumbing components, are addressed primarily by the roofer. During reroofing (recovering or replacement) the roofing contractor is almost always the party responsible for work done to the drainage system regardless of the type.
Let’s answer a couple of general code questions before we start into particular drain requirements. Read More.