In a residential application [or really any other], I understand that a secondary overflow drain is required. In a dual drain scenario, the overflow is required to be 2" above the main drain. Is there a max. height requirement if the overflow is a scupper? For example, the Max. slope of the roof is 4.5", sloped to a centralized roof drain, if a scupper is installed at this height, does it meet code? What section of the plumbing code is this under? Thanks in advance for your input.
Original Post
Let me see if I understand you correctly...

The roof drain is somewhere in the middle of the roof area, and the roof slopes upward from that point to 4.5 inches at the parapet where the scupper is located.

If this is correct, then the entire roof would be under water before the scuppers would even begin to drain, which doesn't seem like a sound solution.

I know California uses the UPC, so I'm not sure exactly what it states, but the IPC indicates that emergency drains or scuppers shall be sized to prevent the depth of water from exceeding that for which the roof was designed. Therefore, you would need to design the roof to support all that water load.

I suggest just putting in the second drain next to the main roof drain.
In SoCal, where it "never rains", many AHJs like to see the overflow at 2-inches above the "regular" drain. Our office standard is for a dual-drain setup, BUT we do institutional work, not residential. We also use overflow scuppers, and set them at 2-inches above the drain height.

With that said, the code does allow for other things as long as the structural capacity of the roof is adequate. Heck, if you are doing an IRMA roof, or a green roof allowing standing water up there could be part of the design.

Mike E
Originally posted by rlga_AZ:
Overflow drains are also required to be piped separately and they cannot be tied into a storm drain system--they must open to daylight so that if water is coming out of the overflow drain, you know there is a problem.

Yup. So you can walk into a store where the overflow is pouring down directly in front of the main entrance and realize that the occupants /employees inside are ignoring it completely. Ask me how I know this; and about the surprised attitude when I mentioned it to the manager... LOL

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