Maximum Drainage Fixture Units

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Old 09-07-14, 08:39 AM
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Maximum Drainage Fixture Units

I want to add a bathroom upstairs and trying to figure out if I am within the maximum Drainage Fixture Units (DFU) allowed. I keep reading up on the subject and still confused so hoping you can shed some light.

I currently have 3 baths. All 3 baths are on the 1st floor with a slab below. I am adding a forth bathroom upstairs. So from what I can find a bathroom group is 6 units so that is 24 units, plus washer 2 units, plus kitchen sink 2 units. It says Kitchen sink with dishwasher, but it is not clear to me if the dishwasher is part of the sink or separate. But with that I have 28 units. All will be run into a 3 waste stack. Below is a picture. The blue 3" line is the new planned line to bathroom group 4. I did not show it on the drawing but all the bathrooms and kitchen are vented separately through the roof.

But I am not clear on the 20 DFU branch maximum. Based on this drawing am I over that limit.

09.07.2014-10.33.06 - rwbil's library
Now this is where it gets confusing.
I am looking at the Florida Plumbing codes, which uses the IPC. I see one table that shows if I have a slope I can do 42 units total for the building and another that talks about 20 units off a single branch.
Is each bathroom unit considered its own branch??
But with 3 baths on the 1st floor and then one on the second feeding into the vertical stack I am confused to how it counts.

I am looking for help in understand what exactly defines a branch and the Maximum DFU and if I am OK or have a problem.

Also a 2nd question. In order to run the 3 upstairs I will have to run it through the attic of the 1st floor and also in the floor joist above the garage. I am in Northern Florida but it can still freeze here. Is there an issue with doing that? I would have the insulation placed above the pipe in the attic and below the pipe in the garage.
 
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Old 09-07-14, 09:03 AM
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Ill have to dive into the code later, but fixture units are more related to venting. Iff all the vents tied into the stack in the attic then you would be over from what I know..

Just pipe the bathroom to code and run the vent seperate off the stack and through the roof.. A standard bath you can run a 1 1/2 vent...

You diagram only shows your proposed vent. It shows no venting for the other baths... If you could show that it would be great...

Such as main stack thats there now, and how all the baths vents are laid out and piped...
 
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Old 09-07-14, 12:16 PM
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Each bathroom group has a vent pipe that goes through the attic. 3 baths - 3 vent pipes through the roof. I will also have another vent pipe for the new bathroom.

But the code says 20 DFUs maximum per branch interval and the definition of a branch interval is a vertical measure of 8' or more. So another way I look at this is the entire 1st floor is one branch and the 2nd floor another branch. If that is the case my 1st floor would be over its DFUs even before adding the 2nd floor bath. But the 2nd floor bath would be its own branch interval so it would not add to the 1st floor branch interval. The whole think is still very confusing.
 
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Old 09-07-14, 03:49 PM
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Its per bath group and whats on that line to the stack... Like I said I will dive into the code to explain better but I may not have time for a few days...
 
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