Bathroom Drain Lines

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PrecisionPlum

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Situation: Existing bathroom with no room to vent shower.
Code for my area is IPC.

PDFs and the jpgs are the same. Whichever work for you.

Your thoughts on this drain line layout.
Any issues with the WC drain entering the stack above the 2" drain?

TIA
 

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You need to vent the shower before it makes that 90 degree turn down and within 6’ after the ptrap
 
You need to vent the 2" shower drain as well. The 2018 IPC allows the vent of a 2" drain line to be 8 feet from the fixture with a slope of 1/4" per foot. The 1 1/2" sink vent can be 6 feet from the fixture, again with a 1/4" slope per foot. All the vents can be tied together, but the tie point needs to be at least 6" above the flood level rim of the highest fixture, the sink in this case. But you also show a sanitary tee "or a wye with 45" for the toilet. That connection to the stack MUST be a sanitary tee, and the drain slope MUST be 1/8" per foot minimum, 1/4" maximum, and within 6 feet of the stack. If it is farther than that, or if you must use a wye and a 45, it will need to separately vented.
 
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MicEd69 said:
The 1 1/2" sink vent can be 6 feet from the fixture, again with a 1/4" slope per foot.
Click to expand...

Seems a little too far but they allow it . 🤡🤷
A lot of codes limit 1.5” fixture arms to 42”. That’s a significant difference, I guess the code writers had a different theory.

The toilet is not limited in distance from the vent.

Section 909.1 Exception. 2018 IPC
 
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I stand corrected on the toilet distance requirement. There is an exception in the IPC code for a water closet. And as such, the use of a wye and a 45 is also permissible as an attachment to the stack.

The distance between the fixture and the vent of a 1 1/2" drain line is not theory, but rather mathematics. At 1/4" slope per foot the distance you can run a 1 1/2" pipe is 6 feet and still maintain proper venting; 1 1/2" divided by 1/4" equals 6 feet. Apparently, the IPC doesn't use any safety factors other than the actual ID of a 1 1/2" PVC pipe being 1.590" instead of 1.5". It would also require the drain to be installed exactly at 1/4" per foot slope which I seriously doubt is ever accomplished. So, I agree it would be best to vent the drain line closer to the trap than 6 feet. There is also a requirement that the vent cannot be closer than 2-pipe diameters to the weir.
 
MicEd69 said:
I stand corrected on the toilet distance requirement. There is an exception in the IPC code for a water closet. And as such, the use of a wye and a 45 is also permissible as an attachment to the stack.

The distance between the fixture and the vent of a 1 1/2" drain line is not theory, but rather mathematics. At 1/4" slope per foot the distance you can run a 1 1/2" pipe is 6 feet and still maintain proper venting; 1 1/2" divided by 1/4" equals 6 feet. Apparently, the IPC doesn't use any safety factors other than the actual ID of a 1 1/2" PVC pipe being 1.590" instead of 1.5". It would also require the drain to be installed exactly at 1/4" per foot slope which I seriously doubt is ever accomplished. So, I agree it would be best to vent the drain line closer to the trap than 6 feet. There is also a requirement that the vent cannot be closer than 2-pipe diameters to the weir.
Click to expand...

Why do some codes limit a 1.5” trap to 42” from the vent ?

Why do some codes limit 2” taps to 6’ ?

What is the reason for the shorter limits in some codes ?
 
As I said, the writers of the codes with shorter maximum distances obviously decided to include a safety factor rather than relying on the math of a perfect installation. ASME codes, structural building codes, NEC/fire codes, etc., ALWAYS include safety factors as they deal with life and death designs. The writers of the IPC apparently do not believe the small amount of suction produced from a full 1.5" pipe due to installation tolerances would pull enough water out of a trap to cause a problem.

I actually have an issue with codes with no safety factors because of the ignorance of the reason for code requirements, especially by the DIYer. If they don't understand the reasoning behind the code requirements, and they know they need to have the drain sloped to gravity drain, and the code says 1/4" per foot, then they could say 1/2" per foot is better and get into trouble. If they happen to be running a long 4" waste line and decide they want to be sure it drains well, so they run it at 1/2" per foot instead of the code's 1/8" per foot, they very well could end up with a stopped-up sewer at some point and never understand why. And they could then use incorrect logic and think the line needs even more slope to drain. Should they then "correct it" by giving it even more slope, they will exasperate the problem of accumulating solids in the line causing additional blockages.
 
MicEd69 said:
As I said, the writers of the codes with shorter maximum distances obviously decided to include a safety factor rather than relying on the math of a perfect installation. ASME codes, structural building codes, NEC/fire codes, etc., ALWAYS include safety factors as they deal with life and death designs. The writers of the IPC apparently do not believe the small amount of suction produced from a full 1.5" pipe due to installation tolerances would pull enough water out of a trap to cause a problem.

I actually have an issue with codes with no safety factors because of the ignorance of the reason for code requirements, especially by the DIYer. If they don't understand the reasoning behind the code requirements, and they know they need to have the drain sloped to gravity drain, and the code says 1/4" per foot, then they could say 1/2" per foot is better and get into trouble. If they happen to be running a long 4" waste line and decide they want to be sure it drains well, so they run it at 1/2" per foot instead of the code's 1/8" per foot, they very well could end up with a stopped-up sewer at some point and never understand why. And they could then use incorrect logic and think the line needs even more slope to drain. Should they then "correct it" by giving it even more slope, they will exasperate the problem of accumulating solids in the line causing additional blockages.
Click to expand...
A safety factor of 2.5’ ? That’s the difference from 42” and 72” distance on the 1.5 dirty arm between different codes. 🤣

I’ve had inspectors that would fail you if it went 42.5”.........

It’s based on their theory.......it’s obviously not based in fact. As I’ve said......✌️
 
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Gee Twowaxhack, you just can't let this go can you.

First of all, factors of safety are not expressed in terms of length, but rather a percentage of a calculated value. As I indicated earlier, 6 feet was obviously established by the pipe ID, 1.5", divided by the pipe slope of 0.25" per foot. Other codes have 42", or a little over 58% of the calculated maximum distance. A 2" pipe has a calculated maximum value of 8 feet (2" divided by the 0.25" per foot slope) and 8 feet is what the IPC allows for 2" pipe. Other codes use 5 feet maximum between a trap and a vent for a 2" pipe. That calculates out to a little over 62% of the calculated maximum value. Based on what I know of industrial codes, I would say that the IPC code writers used 60% of the maximum calculated values, and then rounded that figure to the nearest "standard" length; 3.5 feet and 5 feet. I mean using 43.2" for a 1 1/2" pipe and 57.6" for a 2" pipe would be a little much.

And as an inspector can be a stickler on code issues, an inspector can fail an installation if it does not fully meet the code stated dimensions.

So, as I said, codes are based on calculations and real data, not theory. ;)
 
What’s the real data say that makes a 6’ dirty arm legal by one code but another code only allows a 3.5’ dirty arm ?

2.5’ safety factor ? 🤣

Why would plumbing theory be taught if it wasn’t relied upon in the codes ?

Why would some jurisdictions require plumbing theory class and testing ?

Gee.......that’s a good question.

It’s ok if you don’t agree with me, I’m posting so others can have the information to do as they please with, not to convince you of anything.

Codes differ a lot. That’s just a fact. The writers have theories and they base their minimum standards on these theories.

Here are some differences between the IPC and the UPC.

https://www.iapmo.org/media/25926/resilience-upcvsipc.pdf
 
OK Twowaxhack, you have convinced me. My hang-up was on the word "theory" versus "proven science".

So, I now agree that some of the IPC is based on empirical science, physics, and mathematical calculations, while some other parts are only based on plumbing theories. 🙄
 
MicEd69 said:
OK Twowaxhack, you have convinced me. My hang-up was on the word "theory" versus "proven science".

So, I now agree that some of the IPC is based on empirical science, physics, and mathematical calculations, while some other parts are only based on plumbing theories. 🙄
Click to expand...
I really think you need to take your issues to the IPC, not Twowhacks. He is telling you what it states. If you want to know why, go to them.
 
SHEPLMBR said:
I really think you need to take your issues to the IPC, not Twowhacks. He is telling you what it states. If you want to know why, go to them.
Click to expand...
Actually, I was telling Twowaxhack what the IPC indicated. It was he who was questioning the IPC allowances for the drain arms, not me.

That led to a discussion on codes, so I was just trying to educate him on the background of code development. Not specifically the IPC, but general code factors of safety, of which I have a pretty in-depth understand.
 
Twowaxhack said:
You need to vent the shower before it makes that 90 degree turn down and within 6’ after the ptrap
Click to expand...
Twowaxhack said:
You need to vent the shower before it makes that 90 degree turn down and within 6’ after the ptrap
Click to expand...
Twowaxhack, plesae look again.

Note that there are constrirignts with the original construction
and adding a vent for the shower is not possible.
 
MicEd69 said:
You need to vent the 2" shower drain as well. The 2018 IPC allows the vent of a 2" drain line to be 8 feet from the fixture with a slope of 1/4" per foot. The 1 1/2" sink vent can be 6 feet from the fixture, again with a 1/4" slope per foot. All the vents can be tied together, but the tie point needs to be at least 6" above the flood level rim of the highest fixture, the sink in this case. But you also show a sanitary tee "or a wye with 45" for the toilet. That connection to the stack MUST be a sanitary tee, and the drain slope MUST be 1/8" per foot minimum, 1/4" maximum, and within 6 feet of the stack. If it is farther than that, or if you must use a wye and a 45, it will need to separately vented.
Click to expand...
MicEd69, please see new drawing.
 
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