help with basement rough in. pics included

mamabirrdApril 19, 2008

ok. im looking to rough in the basement plumbing so i can get my floor poured. can you pro's look over this mess and see if this will work. i forgot to include the vent for the floor drain. maybe i can just tie into washer drain? i've included a pic of plumbing and also a floor plan so as to orient yourself. any thoughts are much appreciated.

Here's proposed plumbing layout....

Here's the floorplan...

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ok. i added a side view. i have no illusions of ending up on the front cover of plumbers life. i know the drawings crude. i just wanna get an idea if im on the right track. will it work? will it work with some changes? am i misssing so much i have to buy a book? again any thoughts appreciated.

side view...

    Bookmark   April 19, 2008 at 11:58AM
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The bad news is that all the vents you have shown are prohibited.

The good news is that you don't need any vents.

    Bookmark   April 20, 2008 at 4:52AM
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thank you for the response. i thought all fixtures needed vented. can you please elaborate for me. i appreciate your time.

    Bookmark   April 20, 2008 at 8:01AM
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Everyone is looking for a simple paragraph or two that would explain venting, but I can assure you that such is not possible. Venting is without question the most difficult aspect of plumbing to learn, by example. Typically an approved Plumbing Apprenticeship requires the apprentice to work 40hr/wk (any week with less than 40 hours doesn't count) under a master plumber and the apprentice must attend approved technical school night classes for a period of 4 or 5 years and maintain a minimum 75% passing average. With some very minor exceptions the entire tech school course is based solely upon the respective code in force in the region where the training is conducted and generally 30% of the total classroom time will be spent teaching or discussing venting.

As a side note: statistically 70% of all students who enroll in the apprenticeship will quite the program within the first year and less than 5% will actually complete the entire 4 or 5 year program. If you think Plumbers are expensive now, consider this. According to the U.S. Department of Labor 65% of all licensed plumbers now actively working in the trade are within 10 years of retirement age and there is only 5 applicants to the apprenticeship for every plumber working today. It is anticipated that within 5 to 10 years the price of plumbing labor may double. (If you have teenage boys or girls looking for a career, this is a great field where they can make a lot of money Not only will they work full time, their education is paid for by the employer and you can be sure this field will not be outsourced to China or Mexico).

You are correct that all traps must be vented, however, whenever we mention venting most people instantly think that it requires a separate pipe, which is seldom the case.

If a drain line is properly sized by code standard any horizontal run on that pipe will only be 1/2 full at full rated load. That leaves the upper half of the pipe open for the free movement of vent air.

Any horizontal run of a drain line downstream of a vent connection is classified as a "Vented Branch" or "Vented Main Drain"

The code has a table that lists every type of drain or fixture that may be found in a residential or commercial structure and it mandates the size of the drain opening for that fixture or drain. The table also assigns a DFU (Drainage Fixture Unit) value to that drain. The Trap and drain line should be equal to the size of the drain opening but there is an exception that will allow us to increase the trap or drain size by a maximum of one nominal trade size of DWV approved pipe.

The code also lists all the available DWV grade pipe sizes and it assigns a maximum number of DFU's that may be transmitted through each size of pipe. At every point where two pipes join we must combine the DFU load for each pipe to get a total DFU load at that point. The receiving pipe must then be sized to handle the combined DFU load. (Sizing pipe is very critical because an undersized pipe would not have sufficient volume to permit the movement of vent air and an over-sized pipe will clog quicker than an undersized pipe) The structure "Main Drain" must be sized sufficiently that if every drain in the house was discharging at its full rated load at the same time, the main drain would still only be 1/2 full.

A "Vent Line" is a dry pipe, or one that is intended to convey air but it does not convey any liquids. The codes specifically prohibit any horizontal offsets in a "Vent Line" until that said vent line reaches an elevation at least 6"higher than the flood level rim of the highest fixture served by that vent. The reasoning here is simple. If you have a horizontal run of a vent pipe under the floor in the manner you depicted during normal operation a small amount of solid particulates could back-flow into that vent line then as the liquid recedes the solids could settle to the bottom of the pipe and in the coarse of time they would block the vent.

For a bathroom group we would typically begin at the lavatory drain riser. A tee is placed in the riser to permit connecting a horizontal "Fixture Arm" out to the trap. The vent is then connected to the top of the tee and run up to the roof. The vertical drop and any subsequent horizontal run under that tee are then classified as a "Combined Waste & Vent". This section of pipe may serve as a portion of the vent system because the pipe is continuously washed of any solid particulates by the discharge from the lavatory sink.

One of the most critical points in the DWV system is the "Trap Weir". The "Trap Weir" is the exact point where the U section of the trap turns horizontal forming the trap tail-piece, or in simple terms, the exact point were water passing through the trap would spill out of the U section and into the horizontal tail of the trap. The "Trap Weir" is the exact point were we are required to begin measuring the length of the "Fixture Arm" which is the single pipe that runs from the trap to the stack or horizontal drain receiving the discharge.

The codes state that under no circumstances may a vent be connected closer than 2x the pipe diameter from the Trap Weir.

Up to this point we have discussed the general rules that are common to both the IRC (International Residential Code) and the UPC (Uniform Plumbing Code.) however the IRC & UPC take some dramatically differing views on how it is all put together. From this point I will discuss your design in relation to the IRC. If you happen to be under the UPC let me know and I will post the revisions required.

In your print you have two 4" stacks, one on the opposite side of the interior block wall and the second one slightly downstream from the watercloset (toilet). I have every confidence that both of those stacks terminate through the roof. Let us begin at the stack on the opposite side of the inner wall. All pipe in the main drain downstream of this point is classified as a vented drain line.

Moving downstream the first fixture we encounter is the lavatory bowl. Code standard for a lavatory drain is 1-1/4" however since a lavatory is the only drain in a structure that is permitted to be 1-1/4" most plumbers opt for the code exception which allows us to increase the size of the trap and drain line by one nominal trade size. This allows us to use 1-1/2" pipe rather than maintain a complete inventory of 1-1/4" pipe and fittings for this limited use.

Under the IRC the maximum length of a fixture waste arm can be mathematically computed by dividing the diameter of the pipe by the pitch. Understanding that all pipes less than 3" are required a " per foot pitch we can then determine that the maximum allowable horizontal length of a 1-1/2" waste arm is 1.5 dia. / .25pitch = 5Â. In this case the lavatory bowl is almost directly over the main drain so the total horizontal length of the fixture arm is well under the 5Â max, thus this drain will wet vent from the main drain and there is no additional venting required.

Next we have the washing machine drain. Code requires a washing machine standpipe to be 2" therefore both the trap and waste arm are also 2". 2" dia. / .25"pitch = 8Â max but your drain line will only be 7Â so here again, no additional venting required. The same is true for your floor drain.

A shower is also required a 2" trap and drain, and in this case the shower is well below the 8Â max so it also wet vents from the main drain and no additional venting required.

The watercloset is on a 3" line and the IRC allows a 3" line to be 3"dia. / .25" pitch = 12Â however there is also an exception in the IRC that which states that if a watercloset is the only fixture served by the 3" it may run an indefinitely length from fixture to vent, thus no vent required here either.

So, as I stated before, the bad new is that the vents you propose are code prohibited, but the good news is that you donÂt need any additional venting.

    Bookmark   April 21, 2008 at 10:18AM
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lazypup, i cant thank you enough for this information. it was very nice of you to take the time to explain these things. i now have not just answers, but a better understanding. also thanks for being decent. i tried another forum and was insulted for my ignorance. while it has become clearer to me that there is much more to plumbing drains than meets the eye, i enjoy the challenge and feel you have put me on the right track to completing this rough in

    Bookmark   April 21, 2008 at 8:28PM
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oh yeah and we are IRC here in pennsylvania is my understanding

    Bookmark   April 21, 2008 at 8:41PM
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I can't believe that none of my critics have pointed out the math error in my last post.

In regards to your lavatory drain I mistakenly stated the maximum length of a 1-1/2" line is 5'. Stupid me, the math is right there for everyone to see, 1.5" dia / .25" pitch = 6' not 5'.

I am very sorry that you were insulted in the other forum. Unfortunately we see that level of conduct in all the forums from time to time. Personally I don't believe there is such a thing as a dumb question. If you don't understand then the question makes perfect sense because answering even a dumb question is much easier than undoing a dumb mistake.

P.S. You are correct that the PA Plumbing code is based on the IRC.

    Bookmark   April 21, 2008 at 11:40PM
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Thank you as well from those of us that are silent readers of your knowledge and experience. I enjoy reading your thoughtful and complete explanations and routinely save them to a separate file for future refernce. My only regret (sometimes) is that we follow the UPC.


    Bookmark   April 22, 2008 at 9:36AM
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Wow! I want Lazypup or one of his apprentice graduates to plumb my next house.....

    Bookmark   April 22, 2008 at 9:01PM
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Dear Lazypup,

I agree that your response is fantastic. I am installing basically the same bathroom in basement that is described above. However, I'm in the state of Oregon and I believe we fall under the UPC. I've tried to interpret that guidance for this situation and it sounds like I'm required to use vents, even though I will be well within the maximum distances from the traps to the horizontal vented line. Do you have any suggestions for me?

Thanks, Ed

    Bookmark   May 13, 2011 at 6:48PM
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