Are roof drains required on this large balcony?

[nuuvox000]

I'm trying to figure out when roof drains are required. This is a multi-family housing building and the balcony in question in on the top floor. There is another apartment unit below the large balcony. There is no overhead roof over the large balcony. Are roof drains required here? Or just a floor drain? I can't find anything in the plumbing code that discusses this; curious if overflow drains are required as well. Thanks!

 

[willard3]

This is an HVAC forum.
Not an HVAC question

 

[PEDARRIN2]

If the flow to the drain is from rain/snow, then it needs to go to the storm system, not the sanitary. There are flat strainer roof drains or you can use a flat strainer floor drain. Just make sure the strainer free area is twice the area of the pipe.

You will need a secondary drain if any ponding that might occur from a blockage of the drain/pipe would cause the balcony to collapse due to weight of the water exceeding the strength of the structure or "floor" of the balcony. If there is no parapet or toeboard (not sure that is the correct term), then likely you would not need a secondary drain because any ponding would just sheet over the edge. But if there is any slope on the balcony toward the drain, you will need to check.

And willard3, I would agree this is not a HVAC question, but since the forum administrators removed the plumbing engineering forum and since HVAC engineers/designers do occasionally design the plumbing system - this is the appropriate forum for the question.

 

[nuuvox000]

Yeah, I didn't see a plumbing section and all HVAC engineer firms I know of also do plumbing (at least in Utah).

That's good information Pedarrin2, thanks. Is the strainer free area requirement from code? I know code says that if roof drains are required, then secondary drains are required; I guess I'm just having trouble figuring out if this is a roof. Seems to be in a gray area which maybe just means I have to use my best judgment.

 

[nuuvox000]

Nevermind, reading the code again, secondary roof drains are only required where there is a perimeter wall on the roof area. Not this case here.

 

[PEDARRIN2]

I don't try to distinguish if it is a roof. I distinguish if the water comes from a weather event (rain, hail, snow, run off) or from something else. The former goes to storm. The latter goes to sanitary. A gray area is what do to with "rain" that is on a car in a garage. I send that to sanitary. What the drain is called is not important.

The strainer free area is not in the code, that I am aware. It comes from the manufacturer's literature about grate sizing for interior or exterior use.

Not sure which code Utah uses, but the IPC doesn't explicitly state there has to be a perimeter wall for secondary drains to be required. It just talks about they are required if the roof perimeter construction extends above the roof in such a way that water will be entrapped. This could happen inf the balcony structure slopes to the drain to facilitate drainage or if there is insulation under the roof surface. I have seen differences in elevation of 4" between the edge of a roof and the drain even without a parapet.

 

[nuuvox000]

I also take garage drains to sewer but pass it through an oil separator first. That's a good tip about the strainer.

Another good point about the code. I read the commentary on it and they almost seem to be in contention between sentences. One line says, "A secondary drainage system is required where the building has parapet walls or other construction on the perimeter of the building that would cause ponding." This reads to me that there would be an actual construction element at the perimeter, not just sloping.

Then it says, "The intent of this section is to limit the amount of ponding water that will be placed on the roof by rain-fall. If the building is designed so water cannot pond on the roof, such as roofs sloped toward the edge of the building, secondary drainage is not required." This reads to me that if roofs are sloped away from the edge, then secondary drainage is required.

It seems the intent is to limit ponding on the roof and this would be to avoid structural damage and other issues. I think I'll probably end up checking the slope to see if it's small and see how much water can possibly pond. If it's heavier than a few humans on the balcony then I might add secondary drainage. If not, it doesn't seem to be a dangerous situation.

 

[PEDARRIN2]

1101.7 gives some more info on the why.

We have used the oil interceptor as a "master trap" for the sanitary since most of our garages in Ohio are prone to freezing. This requires acceptance by the AHJ, but generally we get that.

Some of the balconies I have dealt with have had gutters and downspouts. The architect takes care of those.