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I am in the planning stages for adding a full bath to my basement. There is a vertical vent stack nearby that goes into the slab turning into a horizontal run out to the main line from the house. The horizontal run cuts diagonally through my proposed bath layout. My plan is to cut out the concrete and connect to this horizontal section. I searched the forum and found some diagrams for maximum vent distances. Do these distances apply to where I connect to the horizontal (wet vent) pipe or to where the vertical stack enters the slab? The diagrams that I saw all show the sink drain going directly into a vertical stack. Does a sink P-trap always have to have a vertical vent? I have attached a link to a diagram of my layout with the distance from each fixture drain to the vertical stack. The home is located in Virginia.
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Every fixture must have a vent. The distances you are referring to are probably the trap arm length ( the distance from the trap to where a vent is connected) . You must have a vent line from the basement running up either all the way thru the roof,or tying into your main vent stack above the flood rim of the highest fixture connected on that stack. You cannot tie the vents into the main waste stack that you are looking at in the basement.
Depending on what code applies in your town, there is the possibility of using an air admittance valve in place of vent. Not popular with plumbers, but if it is allowed, it is an option for you. -
It is true that every fixture must be vented but there are a number of ways of acheiving that vent. In this case it will be possible to do the entire installation without installing any additional venting because each waste arm will be within the prescribed maximums and therefore it will wet vent back to the Builing Main Drain.
First off, let us consider the Watercloset (Plumbers abreviation WC- common name=toilet). All WC must be set on the end of a waste arm, they may not be tee'd into a line. In this case you can cut the "Main Drain" at a point slightly downstream of the Lavatory position and install a 3" WYE. Off the side opening of the WYE you can install a 1/8 bend (45deg fitting) and run a 3" line back to the WC parallel to the Main drain, turn up with a 1/4 bend and install a closet flange for the WC.
Immediately below the Lavatory you can cut the "Main Drain" and install a 3" x 3" 1=1/2 Wye with the side opening coming off the side of the main drain and running to the wall behind the lavarory. Install a 1/4 bend and an 1-1/2" vertical riser up in the wall, stubbing out to an 1-1/2 trap adapter for the Lavatory. In this case the total horizontal developed length of the waste arm is about 12" from the top of the riser out through the trap adapter and to the trap weir plus about 3' horizontal from the base of the riser to the building "main drain" for a total developed length of 4" which falls well within the maximum 6' for an 1-1/2" waste arm.
At a point about directly under the WC in the drawing you can cut the building "Main Drain" and install a 3" x 3" x 1-1/2" Wye and run an 1-1/2" line to the tub drain. Here again, the overall length of the run is less than the maximum 6' therefore no additional venting is required.Comment
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LazyPup, thank you for the excellent response. I understand everything that you are saying, but just to be clear.....I will need to install a wye into my [u]existing</u> "main drain" at three separate places with the WC wye downstream of the lavatory and bathtub. Correct?
One other thing, my vertical stack is cast iron, so it is fair to assume that the horizontal "main drain" is the same. What method do you suggest for installing the PVC wyes to the cast iron? Fernco rubber couplings?
ThanksComment
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You are correct in the placements of the Wye's.
If you will look in the Illustration forum on Page 2 you will see I have posted two illustrations that will help you:
1: Breaking out a section of Cast Iron Pipe.
2.Joining PVC or ABS to Caat iron pipe.Comment
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LazyPup, thanks for the illustrations. I just had a couple of general questions out of curiosity based on your original reply. The maximum distances, 6' for example on the bathtub, are measured from the bathtub drain to where it connects to the "main drain", since it is a wet vent, correct?
Finally, when you said to install the WC wye downstream of the lavatory, what is the theory behind that? Does the WC always need to be downstream of other devices or did you tell me to do it this way just to create a waste arm for the WC with a little bit of length? Thanks again.Comment
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The developed length of a waste arm is measured in a line on the top of the horizontal pipe from the trap weir (The point were water spills out of a trap) to the vent opening. The vertical section is not measured in, but the vertical riser may not exceed 8 feet.
Under the International Residential Code the maximum developed length of a waste arm may not exceed the diameter of the pipe divided by the required pitch. All pipes 3" or less must have a 1/4" per foot pitch and the tub requires a 1-1/2" trap and drain line so the maximum distance is 1-1/2 divided by .25" = 6'
Generally the size of the drain line is the same size as the trap, and the code requires an 1-1/2 trap for a tub, however there is an exception in the code that will allow us to make the drain line one nominal trade size larger than the trap. (We rely upon that exception for the lavatory which requires an 1-1/4 tailpiece but we often use an 1-1/2" trap and waste arm.) In the case of your tub, if the need arises you could use that exception to increase the drain line to 2" which would then give you 2" / .25" = 8 feet max.
Actually I had a threefold reason for suggesting that placement.
1. A tub or lav waste arm may not be connected downstream of a WC.
2. Allowing a bit of length on the WC waist arm improves the flush action.
3. It allowed sufficient clearance to get the Wye in for the Lav.Comment
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Perfect! I did not know about being able to increase the drain size past the trap by one size. That info may definitely come in handy. Thanks again.Comment
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