# Building drain vs trap arm sizes



## score300 (Feb 1, 2013)

It's been nearly 20 years since I took my test, but I'm sure there was a code that stated that trap arms on a conituous waste and vent system had to be at least 1 pipe size smaller than the trunk line. Am I mistaking or was it once a part of the southern builders code (SBCCI)? I'm not findining it in the international plumbing code now. I'm in a dispute with a restaraunt owner and want to know for sure before I argue any more. He thinks I'm lying to him but I know (or at least I thik I know) that was part of code at one time.


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## Tommy plumber (Feb 19, 2010)

When you say trunk line, you mean the main bldg. drain under the restaurant? Or are you speaking about the vertical drain that the waste arm attaches to?

I am reading 1001.8.3 from the 1994 SBCCI Plumbing Code: _"One trap may be installed for a set of not more than three single-compartment sinks or laundry trays or three lavatories immediately adjacent to each other in the same room, if the waste outlets are not more than 30 inches apart and the trap is centrally located when three compartments are installed."_


I can't find anything regarding your specific situation. I'm not saying you're incorrect, I just haven't found a reference in the '94 code book.


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## AKdaplumba (Jan 12, 2010)

personally Ive never heard a code that states a trap has to be smaller then a trunk line or any other part of a building drain.


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## JoshJ (May 10, 2012)

Can't say I've ever heard of or seen a clause like that in the code book.


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## where am i (Nov 14, 2008)

I would think you would be sizing a trap on what you would be 
using it for. Then you can determine what size pipe to pick up
the trap. Or follow the print.


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## Olemissplumber (Dec 7, 2012)

Add up your fixture units and size your building drain. After that size your branch drains based off their load or application as some fixtures,appliances,appurtenances get special consideration such as equipment with pumps or accept solid wastes.


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## 89plumbum (May 14, 2011)

On combination waste & vent we used to run it all in 4", until one day an inspector came along and said we could run FD's in 3" if we wanted too. Sorry, don't remember how he interpreted that. So I think its more of a preference.


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## Plumbus (Aug 4, 2008)

In my code book, Appendix B (2010 UPC), which hasn't changed in a couple of decades, says _trap sizes are required to be 2 pipe sizes larger then normal and that the tailpieces between fixtures and such traps should be reduced to normal size._ it doesn't mention any required relationship to the trunk line.


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## Phat Cat (Apr 1, 2009)

Test


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## score300 (Feb 1, 2013)

Well guys, It seems this was an unwritten code enforced by Fulton county years back. Instead of questioning the inspectors, I took them for thier word. Looks like I've had a little learning experience here.

I hate it when inspectors make up thier own code!:furious:


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## budders (May 19, 2013)

score300 said:


> Well guys, It seems this was an unwritten code enforced by Fulton county years back. Instead of questioning the inspectors, I took them for thier word. Looks like I've had a little learning experience here.
> 
> I hate it when inspectors make up thier own code!:furious:


Indeed. In new hampshire inspectors don't have to hold a plumbing license or even understand the code. Ive got one who failed my inspection due to a crooked pipe. Even though it held 6 pounds all weekend. He said that he felt it wast in the fitting enough. Same inspector failed me because he wanted a dandy 5 ft from a toilet flange. I say the toilet counts as a c/o. His argument was i came out of the toilet went 3 ft to the main stick and turned and followed it till i hit my 4 by 3wye. And because i changed direction that i was required to put one in. I argued if the line backed up i would pull the toilet first before going and opening a dandy thats full. He eventually one cuz i needed the inspection to pass


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## plbgbiz (Aug 27, 2010)

budders said:


> Indeed. In new hampshire inspectors don't have to hold a plumbing license or even understand the code. Ive got one who failed my inspection due to a crooked pipe. Even though it held 6 pounds all weekend. He said that he felt it wast in the fitting enough. Same inspector failed me because he wanted a dandy 5 ft from a toilet flange. I say the toilet counts as a c/o. His argument was i came out of the toilet went 3 ft to the main stick and turned and followed it till i hit my 4 by 3wye. And because i changed direction that i was required to put one in. I argued if the line backed up i would pull the toilet first before going and opening a dandy thats full. He eventually one cuz i needed the inspection to pass


No...he won because he was right.


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## wyrickmech (Mar 16, 2013)

score300 said:


> Well guys, It seems this was an unwritten code enforced by Fulton county years back. Instead of questioning the inspectors, I took them for thier word. Looks like I've had a little learning experience here.
> 
> I hate it when inspectors make up thier own code!:furious:


Them making up stuff is easy to debunk if you know your codes. What is really fun is when you have a good inspector that knows what he is talking about. The challenge then gets interesting you will learn a lot that way. When the inspector asks you why you did something and then says ( I didn't know that) that is annoying.


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## crown36 (May 21, 2013)

budders said:


> Indeed. In new hampshire inspectors don't have to hold a plumbing license or even understand the code. Ive got one who failed my inspection due to a crooked pipe. Even though it held 6 pounds all weekend. He said that he felt it wast in the fitting enough. Same inspector failed me because he wanted a dandy 5 ft from a toilet flange. I say the toilet counts as a c/o. His argument was i came out of the toilet went 3 ft to the main stick and turned and followed it till i hit my 4 by 3wye. And because i changed direction that i was required to put one in. I argued if the line backed up i would pull the toilet first before going and opening a dandy thats full. He eventually one cuz i needed the inspection to pass


What in the hell is a 'dandy'? Perhaps I'm just not familiar with that term. Are you referring to a test tee?


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## wyrickmech (Mar 16, 2013)

score300 said:


> Well guys, It seems this was an unwritten code enforced by Fulton county years back. Instead of questioning the inspectors, I took them for thier word. Looks like I've had a little learning experience here.
> 
> I hate it when inspectors make up thier own code!:furious:


There is a little food for thought here.If the building drain is sized for the whole building ,sized per fixture units why would one fixture be as big? There is no reason for it to be big enough to carry the entire building. Over sizing is as bad as under sizing. A few years back I learned the hard way that a line which only has two stools on it should not be 4 in going into a double wye the fluids will simply flow past the solids. If it would have been 3 in it would have carried the solids away.


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## pipes (Jun 24, 2008)

Triplecrown24 said:


> What in the hell is a 'dandy'? Perhaps I'm just not familiar with that term. Are you referring to a test tee?


 
Yes he is referring to a test tee. We have lots of special little names for fittings , like "Boston ty's" "estabrooks" "owl fitting" . 
Please do not look at me for this stuff, I just came up the ranks hearing it.


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## wyrickmech (Mar 16, 2013)

pipes said:


> Yes he is referring to a test tee. We have lots of special little names for fittings , like "Boston ty's" "estabrooks" "owl fitting" .
> Please do not look at me for this stuff, I just came up the ranks hearing it.


Proper terminology does not always make it threw the ranks.


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## crown36 (May 21, 2013)

pipes said:


> Yes he is referring to a test tee. We have lots of special little names for fittings , like "Boston ty's" "estabrooks" "owl fitting" .
> Please do not look at me for this stuff, I just came up the ranks hearing it.


Who is 'We'? Plumbers in general? Is that what you're saying?


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## bighutch (Feb 14, 2012)

toatal fixture units


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