Is this DWV plan compliant with UPC?

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Brian Nagy

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wwhitney

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I assume "tee" means "san-tee". Then as far as the DWV sizing and layout, yes, as long as the closet bend plus the vertical WC fixture drain add up to less than 19" in length. From the closet flange to the 3" san-tee is limited to 72" measured along the pipe.

Not sure about cleanout requirements; I would think it would be better to move the 3x2 reducer above the cleanout and use a 3" cleanout. The building needs another 2" vent through the roof somewhere, as the aggregate area of vents through the roof needs to be at least the same as a 3" vent.

For the shower trap arm to be so short with a vertical dry vent, I guess it must be a trench drain at one edge of the shower?

Cheers, Wayne
 

Brian Nagy

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Thank you for the reply. I was not aware that the tailpiece before the closet bend was considered part of the trap arm in the 6' limit for the WC. I think I'm cutting it close, but I'm probably good. My CAD model measures the tailpiece at 14.25" down from the flange into the hub of the closet bend, and the horizontal pipe is 50.25" from inside the hub of the closet bend into the tee hub. Together, that is 64.5" of straight pipe, leaving 9.5" to stay within the 72" code limit. I'm not sure what the lengths of the curve through the bend and the curve to the vent inside the tee are. It seems to be less than 9.5".

I cannot put the reducer above the cleanout. The reducer butts up against the subfloor. The largest pipe I can run up through that wall is 2" without violating the 60% bore limit. I don't believe I actually need to have a cleanout there since I have a two-way cleanout at the lower end of the building drain which means I don't need one at the upper end, according to code. I just have it there for convenience, so I don't need to go down the vent from the roof to clear any blockages, although I don't foresee any blockages ever developing in the drain given how extremely overengineered everything is in the code and how my layout has the shower and lav. flushing out solids.

The shower is a standard minimum-size (30" internal circle) corner shower with the drain 12" from each corner wall. I've got the vent in one shower wall (the only wall in the bathroom through which pipes can be run up through the bottom plate). It is a tight fit, but at 8", it complies with the 4" minimum trap arm for a 2" pipe.

It is my understanding of the code requires the aggregate area of building vents to be sufficient to vent the building drain. By code, the vent area only needs to be half the area of the drain served. A 3" drain pipe has an actual internal cross-sectional area of 7.43 square inches, so code requires the vents serving that drain to have an aggregate cross-sectional area half that (i.e. 3.72 square inches). Together, a 2" vent and 1.5" vent have an actual internal aggregate cross-sectional area of 5.42 square inches, well in excess of the requirement. This building drain only serves one 6 DFU bathroom group in the addition, and together, the 2" vent and 1.5" vent are sufficient to vent 32 DFUs! It is way overengineered in terms of venting, especially considering the fixture flow restrictions imposed by Title 15. The maximum flow rate through the entire drain system will be a measly 3 gpm (1.2 gpm for the lav and 1.8 gpm for the shower if they are both running full bore). Even if we assume the flow restrictors are removed and the 1/2" supply lines are allowed to run free, the maximum output would only be 50-60 gmp. Together, a 2" vent and 1.5" vent can supply at a sufficient rate to replace the amount of air displaced by a flow rate of 325 gpm. In other words, a 2" vent and 1.5" vent supply more than five times as much venting capacity as this building drain could ever possibly require in a worst-case condition. But I understand where you are coming from; the code is very badly worded and can be interpreted to mean that the aggregate vent size must equal the drain size even though such a requirement would be patently ridiculous. Of course, a lot of the code is patently ridiculous, so I can see the city requiring me to waste a lot of resources and weaken the building structure running an additional totally useless vent.

Thanks again for the input. Yours is the only feedback I've gotten on any of my posts on any plumbing forums. I appreciate it!
 

wwhitney

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Thank you for the reply. I was not aware that the tailpiece before the closet bend was considered part of the trap arm in the 6' limit for the WC.
See footnote 2: https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/10/traps-and-interceptors#1002.2


I cannot put the reducer above the cleanout. The reducer butts up against the subfloor. The largest pipe I can run up through that wall is 2" without violating the 60% bore limit.
I don't follow that, as the bore limit is for studs, not the bottom plate. You could cut away the bottom plate completely in a stud bay. Even in a load bearing wall, there is no load on the bottom plate in between studs. [For a shear panel, the bottom plate is important as one of the edge members.]

It is my understanding of the code requires the aggregate area of building vents to be sufficient to vent the building drain. By code, the vent area only needs to be half the area of the drain served.
That is not my understanding. The following sentence is from this reference: https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/9/vents#904.1

"In addition, the drainage piping of each building and each connection to a public sewer or a private sewage disposal system shall be vented by means of one or more vent pipes, the aggregate cross-sectional area of which shall be not less than that of the largest required building sewer as determined from Table 703.2"

As any building with a WC requires a 3" drain for the WC and hence at least a 3" building sewer, any building with a WC requires an aggregate roof vent area equivalent to at least a 3" vent.

The IPC certainly agrees with you that this is overengineered.

Cheers, Wayne
 

Brian Nagy

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I agree with you. I went back through the code and found the UPC footnote that explicitly includes the w.c. tailpiece in the length determination for the trap arm of the fixture. It is not the case in IPC, and quite frankly, it is without merit. The entire reason for a trap arm length limit has to do with the slope and diameter of the horizontal run of the trap arm such that top of the horizontal trap arm at the vent is not lower than the bottom of the horizontal run at the trap weir because that would cut off air flow from the vent to the fixture, rendering the vent useless. The tailpiece has no bearing whatsoever on the matter; however, whoever wrote that footnote into the UPC evidently didn't quite understand the actual physics and hydraulics that are the reason for trap arm length limits. That footnote has no scientific basis, theoretical or empirical. Alas, the law is the law, and We The People have no standing to reasonably question unreasonable laws in this society, so I have no choice but to comply.
https://st.hzcdn.com/fimgs/a712df5b04b92271_9642-w500-h569-b0-p0--.jpg


I agree with you completely about the bore limits, especially in non-load-bearing partition walls. Alas, the code is ambiguous, and in my experience, the city building department and inspectors always go with the most restrictive and onerous interpretations in cases of code ambiguity. My own city nixed my first DWV plan because they would not permit me to run a 2" vent up the extant 2x4 partition wall (non-load-bearing and not a shear wall) without bracing the bottom and top plates with 16-gauge steel reinforcing plates extending at least 6" beyond the bore on both sides. Alas, there are not 6" to one side of where the vent must go, so I couldn't meet that requirement. Thus, I was required to knock out the existing wall and build a new 2x6 wall for the vent pipe. If I step up to a 3" vent, I will run up against the same restriction that will require steel reinforcing straps that there is no room for and will need to scale up to a 2x8 wall, and there is not enough room for that thick a wall. Thus, I need to stick with a max 2" vent in this instance.


I agree with you about aggregate vent area for the building drain. Your understanding is the most straightforward and accurate way to literally interpret the code, and having looked at the requirements of several cities, I find that they all interpret the code the same as you. I believe, however, that the code was just badly written in this case, and the actual intent was for it to say "the aggregate cross-sectional area of which shall be not less than that required by the building sewer as determined from Table 703.2." Written in this way, the requirement would be identical with IPC and would make perfect sense. I believe there was an editing error during initial publication that has become entrenched and no one is willing to use critical thinking, admit the typo, and correct the code to be reasonable. Besides, excessive requirements make more profit for most of the stakeholders involved in producing the code. Requiring bigger pipes means the pipe manufactures get to sell more product, lumber companies get to sell more lumber for wider walls, Simpson gets to sell more strongtie straps, flashing companies get to sell more flashing, plumbers get more work replumbing older buildings to meet excessive standards, and cities make more money on extra permit fees. The only stakeholders who might raise an alarm are environmentalists because of all of the extra plastic and deforestation caused by excessive requirements, but we all know that environmental concerns are only considered with respect to things that will generate profits for the other stakeholders.

Fortunately, I think I am okay with the aggregate venting in my case because of the Exception to 904.1.
https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/9/vents#904.1
"Where connected to a common building sewer, the drainage piping of two or more buildings located on the same lot and under one ownership shall be permitted to be vented by means of piping sized in accordance with Table 703.2, provided the aggregate cross-sectional area of vents is not less than that of the largest required common building sewer."
This 3" building drain from the 1986 addition to the house connects to the 4" building sewer from the original 1942 house. The original house has a 1.5" vent and a 3" vent. Ironically, that does not meet the UPC requirement. A 1.5" vent has an actual internal cross-sectional area of 2.05 square inches, and a 3" vent has an actual internal cross-sectional area of 7.43 square inches; together, they have an aggregate cross-sectional area of 9.47 square inches which is not equal to the cross-sectional area of the 4" building sewer, which is 12.77 square inches. Of course, we have lived here for over 40 years and have never had a venting problem.
My DWV plan that adds this bathroom group will add a 2" vent (actual internal cross-sectional area of 3.37 square inches) and 1.5" vent (actual internal cross-sectional area of 2.05 square inches) to the system. Together, they add 5.42 square inches of venting. Combined with the 9.47 square inches of venting extant in the original house, that gives a total aggregate cross-sectional vent area of 14.9 square inches, which exceeds the 12.77 square inches that UPC seems to require for the 4" common building sewer. Whew!

Thank you for your feedback. It has helped me greatly to annotate my DWV plan. I will specify "sani-tee" to make that unambiguous. I will add a red centerline and specify the total trap arm length from the flange to the vent to indicate that it is less than 6'. I will note the applicability of the exception to 904.1 due to this 3" building drain connecting to the common 4" building sewer already served by a 3" vent and 1.5" vent. And I will note Exception 4 to 707.4, indicating the two-way cleanout at the lower end of the 3" building drain that exempts the requirement for a cleanout at the upper terminal so the city does not try to exert control over the placement of my cleanout on the 2" vent.

My main concern was actually that the wet vent would run afoul of the code. When it comes to wet venting, I find the UPC to be clear as mud. But you didn't flag that play, so that gives me some peace of mind, although what the city will say is another story.

Thanks again!
 
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Reach4

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The entire reason for a trap arm length limit has to do with the slope and diameter of the horizontal run of the trap arm such that top of horizontal trap arm at the vent is not lower than the bottom of the horizontal run at the trap weir because that would cut off air flow from the vent to the fixture. The tailpiece has no bearing whatsoever on the matter.
Toilets are different. The weir is in the toilet. The trap is supposed to siphon out, and then gets refilled.
 

Brian Nagy

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I agree with you. The actual weir that provides the water seal is within the toilet fixture itself, and this is why the IPC explicitly excludes toilets from the requirement that the vent opening not be entirely below the weir of the trap; it is physically impossible for a toilet to meet that requirement. However, the fact remains that the sole reason for a length limit on a horizontal run of a trap arm is to prevent the top of the horizontal pipe at the vent from being below the bottom of the pipe at the upper end. For this purpose, the closet bend is generally identified as the "weir" of a toilet (even though it isn't really). The vertical tailpiece from the flange down to the closet bend has no bearing on the matter since it is not part of the horizontal run; it is the horizontal run that needs to be limited based on the pipe slope. See the linked diagram.
https://st.hzcdn.com/fimgs/a712df5b04b92271_9642-w500-h569-b0-p0--.jpg
 

wwhitney

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I agree with you completely about the bore limits, especially in non-load-bearing partition walls. Alas, the code is ambiguous, and in my experience, the city building department and inspectors always go with the most restrictive and onerous interpretations in cases of code ambiguity. My own city nixed my first DWV plan because they would not permit me to run a 2" vent up the extant 2x4 partition wall (non-load-bearing and not a shear wall) without bracing the bottom and top plates with 16-gauge steel reinforcing plates extending at least 6" beyond the bore on both sides.
That position is completely indefensible, as R602.6.1 starts off " Where piping or ductwork is placed in or partly in an exterior wall or interior load-bearing wall, necessitating cutting, drilling or notching of the top plate by more than 50 percent of its width, a galvanized metal tie not less than 0.054 inch thick (1.37 mm) (16 ga) . .." So the requirement does not apply to interior non bearing walls; your building department is wrong.

https://up.codes/viewer/california/irc-2018/chapter/6/wall-construction#R602.6.1

Also, the requirement does not apply to the bottom plate.

the actual intent was for it to say "the aggregate cross-sectional area of which shall be not less than that required by the building sewer as determined from Table 703.2."
I don't think I'm convinced by your argument as to the intention, because for small buildings with 3 or fewer WCs, the minimum required (a modifier you left out) building sewer is only 3", so your language would only require a 1-1/2" vent for the whole building. Which is incongruous with the requirement of a 2" vent for any WC.

The original house has a 1.5" vent and a 3" vent. Ironically, that does not meet the UPC requirement.
It does if the house has 3 or fewer WCs. Because the requirement references the minimum required building sewer size, rather than the actual building sewer size. So with 3 or fewer WCs, the building sewer could have been 3", so you only need a single 3" vent.

Cheers, Wayne
 
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Brian Nagy

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I agree with you. I was outraged by being required to replace the 2x4 wall with a 2x6. It creates a huge mess, it creates a lot of unnecessary waste for the landfill, it adds significant effort and time to the project, and considering that the price of building materials and disposal fees have skyrocketed this year, it adds A LOT to the overall project cost. It also requires a supplemental $50 construction permit (in addition to the separate plumbing and electrical permits) and another plan check fee, so the city makes a tidy profit for itself by forcing me to do it. I'm furious about it. But, lemonade out of lemons, it allows me to move the wall out three inches to have a little more space inside the small bathroom. As it was, the base of the shower violated the 15" standoff to the centerline of the toilet. The glass wall of the shower was clear of the standoff, which I believe should be sufficient since the spirit of the code requirement is elbow room for a person at the toilet, but the city would probably disagree and go with the strictest interpretation of the rule. They're always going to find some nitpicky way to force major reconstruction, no matter what. In response to my objections, the department representative I spoke with said, "It is because of the two-inch vent rule that we mandate a minimum 2x6 wall for plumbing in all new construction." It wasn't going to be new construction to begin with; it was just installing the fixtures into the existing space built in 1986, but now it is a huge ordeal. I really dislike my city. All of the authorities here are jerks about everything, and the fee schedules are outrageous. Tradespeople hate doing any work in this city if it requires a permit. Alas, I'm trying to be above-board and law-abiding. Big mistake!
 

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I agree with you. The actual weir that provides the water seal is within the toilet fixture itself, and this is why the IPC explicitly excludes toilets from the requirement that the vent opening not be entirely below the weir of the trap; it is physically impossible for a toilet to meet that requirement. However, the fact remains that the sole reason for a length limit on a horizontal run of a trap arm is to prevent the top of the horizontal pipe at the vent from being below the bottom of the pipe at the upper end. For this purpose, the closet bend is generally identified as the "weir" of a toilet (even though it isn't really). The vertical tailpiece from the flange down to the closet bend has no bearing on the matter since it is not part of the horizontal run; it is the horizontal run that needs to be limited based on the pipe slope. See the linked diagram.
https://st.hzcdn.com/fimgs/a712df5b04b92271_9642-w500-h569-b0-p0--.jpg

I think when it comes to venting requirements you're a little off on your thinking. The UPC is striving to keep the atmospheric pressure inside of the system. Since air is compressible and a toilet flushing can cause air velocity to change quite a bit, this causing possible vaccum or above atmospheric conditions.

The code is actually the minimum requirement to keep those conditions. The code is based on lab testing and consensus among people in the industry. If you have a trap that's seal is constantly being tumbled and sloshed about the threat of sewer gas is enhanced, let alone just normal trap evaporation under atmospheric conditions.

Further, imagine yourself writing a code. You have to write something (an american standard) that can guarantee public safety and stand up to lawsuits along with being practical. It's a tougher thing than it seems.
 

James Henry

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I think when it comes to venting requirements you're a little off on your thinking. The UPC is striving to keep the atmospheric pressure inside of the system. Since air is compressible and a toilet flushing can cause air velocity to change quite a bit, this causing possible vaccum or above atmospheric conditions.

The code is actually the minimum requirement to keep those conditions. The code is based on lab testing and consensus among people in the industry. If you have a trap that's seal is constantly being tumbled and sloshed about the threat of sewer gas is enhanced, let alone just normal trap evaporation under atmospheric conditions.

Further, imagine yourself writing a code. You have to write something (an american standard) that can guarantee public safety and stand up to lawsuits along with being practical. It's a tougher thing than it seems.







Exactly... His naggy attitude and disrespect for inspectors probably doesn't help either. You don't fight with the building department.
 

Brian Nagy

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I agree, that is plausible. I am not aware of any lab testing that was done to establish these UPC standards. In IPC, used internationally and by more than twice as many US states as is UPC, there is no such requirement, and the plumbing works without problem, providing an enormous volume of broad-scale empirical evidence that calls the UPC requirement into question. It should also be noted that the conventionally accepted requirement for an oversized 2" vent for a w.c. in the UPC (implied by a table footnote, but not explicitly stipulated) also is not supported by any empirical evidence since most of the world's plumbing systems use a 1.5" w.c. vent (as required by IPC) where that works just fine. I have seen no scientific studies supporting the UPC requirements. If someone has a link to a technical whitepaper with lab results that back up the UPC requirements, I would like to see it. It might be out there. However, having worked in bureaucracies, I am aware that mistaken wording and typos can become formalized as policy and afterword be very difficult to correct. I suspect that may be what has happened with the UPC. Of course, the law is the law, and what is written is written. So even if it doesn't make sense and is not supported by science or factual evidence, we must obey. We have no right to question the law here.
 

John Gayewski

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I agree, that is plausible. I am not aware of any lab testing that was done to establish these UPC standards. In IPC, used internationally and by more than twice as many US states as is UPC, there is no such requirement, and the plumbing works without problem, providing an enormous volume of broad-scale empirical evidence that calls the UPC requirement into question. It should also be noted that the conventionally accepted requirement for an oversized 2" vent for a w.c. in the UPC (implied by a table footnote, but not explicitly stipulated) also is not supported by any empirical evidence since most of the world's plumbing systems use a 1.5" w.c. vent (as required by IPC) where that works just fine. I have seen no scientific studies supporting the UPC requirements. If someone has a link to a technical whitepaper with lab results that back up the UPC requirements, I would like to see it. It might be out there. However, having worked in bureaucracies, I am aware that mistaken wording and typos can become formalized as policy and afterword be very difficult to correct. I suspect that may be what has happened with the UPC. Of course, the law is the law, and what is written is written. So even if it doesn't make sense and is not supported by science or factual evidence, we must obey. We have no right to question the law here.
I haven't taken the time to track down lab test reports. I can only say that articles available online and written by iapmo will refer to testing done in labs. I can also say that most every time I find a problem in the field, it can be traced,either directly or indirectly, to something that wasn't quite done to code. Someone doesn't use the correct fitting or an improper vent configuration will lead to a drain slowing. Then there's the 1/4" slope. That one often times doesn't get fully implemented. People oversized pipe very often, which isn't most times explicitly prohibited by code, but I find it to underperform.

The dispute would be not how much air can possibly move through a 2" or a 1.5" pipe (as you imply above). The issue would be how much does actually flow when the system is performing with all of the dynamics in place. Have you ever walked into your bathroom and stood over the toilet only to see the water seems to be bulging and receding, slowly and slightly? Keep in mind your system is hooked into the main city sewer. There can be some major disruptions and "events" in that large interconnected system.

I'm not saying any of this to imply your points don't have merit, just that there's more to think about than how much air can pass through a pipe.
 

Jeff H Young

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I agree with you. I was outraged by being required to replace the 2x4 wall with a 2x6. It creates a huge mess, it creates a lot of unnecessary waste for the landfill, it adds significant effort and time to the project, and considering that the price of building materials and disposal fees have skyrocketed this year, it adds A LOT to the overall project cost. It also requires a supplemental $50 construction permit (in addition to the separate plumbing and electrical permits) and another plan check fee, so the city makes a tidy profit for itself by forcing me to do it. I'm furious about it. But, lemonade out of lemons, it allows me to move the wall out three inches to have a little more space inside the small bathroom. As it was, the base of the shower violated the 15" standoff to the centerline of the toilet. The glass wall of the shower was clear of the standoff, which I believe should be sufficient since the spirit of the code requirement is elbow room for a person at the toilet, but the city would probably disagree and go with the strictest interpretation of the rule. They're always going to find some nitpicky way to force major reconstruction, no matter what. In response to my objections, the department representative I spoke with said, "It is because of the two-inch vent rule that we mandate a minimum 2x6 wall for plumbing in all new construction." It wasn't going to be new construction to begin with; it was just installing the fixtures into the existing space built in 1986, but now it is a huge ordeal. I really dislike my city. All of the authorities here are jerks about everything, and the fee schedules are outrageous. Tradespeople hate doing any work in this city if it requires a permit. Alas, I'm trying to be above-board and law-abiding. Big mistake!

I love LA but wont live there again . visit a few times a year , I enjoy south OC San Clemente to North SD Carlsbad if I go to coast or bypass LA and north , santa Barbara or SLO Brother lives By La Canada / flintridge Montrose area close to glendale its ok over there close to all the hustle and bustle yet no bums living on the sidewalk.
its a good time to sell!
 
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