I've been asked to writeup a section on scuppers for our design guidelines. Typically we go with a BUR sloped to drain to the interior, so I've never really dealt with scuppers.

What are some pros/cons of these things? The only time I've ever seen them they have been poorly installed on a canopy roof. They seem like they would ice up as well. Only reason I can see using them is if there was an absolute need for a parapet at the low point of a roof.

Thanks for the help!

interior drains are lot better than a scupper. there really only good for overflow backup.

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When I've seen them used on residential they are normally sloped to the scupper and it is dumped into a gutter system. On newer commercial apps, they are used as an overflow in case of debris stopping the roof drains. I've been on two that were designed as the drainage for the buildings. Both roofs were leaking at this point. For some reason, everyone tries to torch multiple layers of GTA on these to stop leaks. Different areas of the country may have different apps. It might be code in some areas. I know the local target store was only open for a year when we got a huge downpour and the roof drains couldn't handle it. Down came the roof into the store.

Here in Ca. they are used all the time when you need to go through a parapet wall as a main drain. Code here requires that you install a overflow 2" higher then the top of the scupper. I dont know how it would work in snow country, Since it never snows by the beach.

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I'm going to guess you meant the overflow drain is to be 2" higher than the bottom of the scupper, not the top. Typically, overflow drainage elements are supposed to be 2" above finished roof at primary drainage element, so in theory your roof should never hold more than 2-inches of water if a drain gets clogged. If you did it from the top of the scupper, you could have a 12-inch tall scupper that gets clogged and you would accumulate 14-inches of water before the overflow is functional, which obviously won't be a good thing for your roof and structure.

Now, if the scupper is going to be used as a primary drainage element, it needs to be properly sized, properly flashed, utilize a face-plate, and discharge into a conductor-head and downspout.

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Professional Roofing & Waterproofing Consultant

Another thing to consider is where the scupper starts will be on the roof, or waterproofed side. Where the scupper exits will be on a side with a water draining material (i.e., brick, CMU, Plaster, Concrete), not water shedding. In my experience many leaks occur at scuppers on the exit side. Also with expansion and contraction of the sheet metal scupper as it freezes and warms up, water can wick back into the wall and deteriorate surrounding material. Especially if the primary scupper drains into a rain gutter leader head. Extra steps need to be taken to prevent these types of problems. Overflow scuppers should always be open for view from the ground so that when water is seen draining from them, then you know your primary drain or scupper drain is clogged.

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I'm going to guess you meant the overflow drain is to be 2" higher than the bottom of the scupper, not the top. Typically, overflow drainage elements are supposed to be 2" above finished roof at primary drainage element, so in theory your roof should never hold more than 2-inches of water if a drain gets clogged. If you did it from the top of the scupper, you could have a 12-inch tall scupper that gets clogged and you would accumulate 14-inches of water before the overflow is functional, which obviously won't be a good thing for your roof and structure.[/quote]

You got a point there. Thats how I saw it.The Building Inspectors want it 2" or to the top corner of the scupper and that was on a 4" scupper. any bigger and you wont need an overflow it wouldn't have a roof to drain. We always tilt out scuppers downwards that way it help the water drain better and it wont wick back always seal around the exterior wall.

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2nd Gen. roofing contractor.
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