Bathtub Rough-In: tub drain, p-trap, secondary drain line

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Tony5289

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I appreciate your advice on this freestanding bathtub rough-in done by my renovation contractor.
  1. Is this set-up correct? If not: what is wrong with it?
  2. If we used this set-up: what might be bad impact/consequences?
  3. Most important: What should be the correct and best/practical set-up?
Please note:
  • The 1 ½” tub drain pipe should remain in same vertical location. Everything below it can change.
  • The 1 ½” p-trap’s “U” (hidden by the trap arm) currently sits on the floor board.
  • The 1 ½” secondary drain pipe flows from right to left (it's a straight pipe that runs along top edge of the 8” x 8” bulkhead):
    • Before the sanitary tee: this secondary drain pipe starts 8 ft upstream with a vented pipe (at vanity sink’s drain).
    • After sanitary tee: this pipe continues 3 ft downstream to a vented pipe... and then another 3 ft to a 3” primary drain pipe (which has another vented pipe).
Thanks. I'm just the house owner with no plumbing experience.
Tub Rough In.JPG
 

Tony5289

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There should be NO "secondary drain pipe", and you have an illegal "S" trap, NOT a "P" trap.

Hi hj. Thanks for your prompt and helpful comments.
  • You confirmed that it is an s-trap and must be eliminated. (I did not know that just a 5” vertical drop from trap arm would make it an s-trap)
  • Understood on the 1 1/2 ‘horizontal’ drain pipe. (In any case, I should have called this the ‘main line’ or ‘main drain pipe’ instead of “secondary drain pipe”).
  • I guess the sanitary tee connecting the two intersecting drainpipes is incorrect (in any case it's irrelevant since there should be no secondary drain pipe).
How should this set-up be re-designed to fix this situation? Notes:
  • please keep the 1 ½” tub drain tailpiece pipe in the original vertical location (as it was aligned for tub drain hole location).
  • we can use the 8” x 8” bulkhead which is infront and below the existing 1 ½” horizontal drain pipe (the bulkhead is littered with 3 or 4 waste wood pieces that can be removed)
Sorry in advance if I use the wrong terms, rules or principles. I'm learning on the fly.
Finally, I'd like to thank this website's owners and contributors for providing the info that helped me decide to buy four Toto Ultramax II toilets as replacements. They're working beautifully.
 

Reach4

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You confirmed that it is an s-trap and must be eliminated. (I did not know that just a 5” vertical drop from trap arm would make it an s-trap)
It is not having the trap arm vented that make it an S trap.

I don't know how to readily correct that, but what contract did you have with your contractor? Normally it would be up to the contractor to remedy, I would think.
 

Tony5289

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It is not having the trap arm vented that make it an S trap.
I don't know how to readily correct that, but what contract did you have with your contractor? Normally it would be up to the contractor to remedy, I would think.

Thanks Reach4. Unfortunately, the contractor believes there is nothing wrong with this set-up. He says this method works and has been used for a long time.
 
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Tony5289

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Would the following proposed re-design (light blue line in picture) correct the issues in the original set-up (listed after picture)? Kindly provide your advice and suggestions only if there are mistakes in the re-design. Thanks.
  • The 1.5” tub drain tailpiece pipe (remains at original vertical location, which was pre-aligned for the tub) will connect to…
  • a 1.5” pipe, which then will slope at 45-degrees for about 8” to 11” in order to connect to...
  • the 1.5” p-trap (which will be re-located to below the joists and inside the bulkhead – so that top of trap will be parallel to the adjacent existing 1.5” horizontal waste pipe)…
  • the trap arm (below joists and inside bulkhead) will flow in one of the following two alternative paths:
(a) the trap arm will continue horizontally for 3 ft at 1/4” per foot slope to connect (with an approved fitting: a Wye; a Combination Wye and 1/8 Bend; or the only other approved fitting of equivalent sweep, i.e., Wye + an 1/8 Bend) to this existing 1.5” horizontal waste pipe (near where this waste pipe intersects with a vent pipe)
OR
(b) after trap outlet, the trap arm will immediately make a horizontal change in direction to connect (with an approved fitting: a Wye; a Combination Wye and 1/8 Bend; or the only other approved fitting of equivalent sweep, i.e., Wye + an 1/8 Bend) laterally to the adjacent existing 1.5” horizontal waste pipe, which will continue for 3 ft at ¼” per foot slope to the this waste pipe’s intersection with the vent pipe.​

Tub Rough In -- Proposed.jpg


The issues in the original set-up which need to be corrected (based on hj's and Reach4's comments as well as my layman's reading of the UPC and IPC):
  • The current trap and trap arm is an S-trap. This type of trap is prohibited in a drainage system (UPC 1004.1, IPC 1002.3).
  • The current trap and trap arm are located too high in relation to the vent/waste pipe. The trap arm's excessive slope is far beyond 1/4 inch per foot slope toward the vent/waste pipe fitting (UPC 1002.2, IPC 909.1, UPC 708.1, IPC 704.1). The vent pipe opening is below the trap weir (UPC 1002.4, UPC 905.5, UPC 908.2.3, IPC 909.2).
  • The current ‘trap arm’ flows in an improper direction (horizontal-vertical-horizontal changes in direction): (a) greatly exceed the 1/4" per foot slope for a 1.5" pipe and (b) turn the trap and trap arm into an illegal trap (S-trap). The only change in direction permitted for a trap arm is a horizontal to horizontal change in direction. The UPC and IPC do not mention horizontal-to-vertical or vertical-to-horizontal changes in direction for a trap arm. (UPC section 1002.3, UPC 706.3, UPC 706.2, UPC 706.4, IPC 706)
  • A Sanitary Tee is the wrong fitting to connect the vertical trap arm with the horizontal waste pipe. The only approved fittings for connecting a vertical/horizontal drainage line with a horizontal drainage line are the following: Wye (45 degree), Combination Wye and 1/8 Bend, or the only other approved fitting of equivalent sweep – Wye + an 1/8 Bend (UPC 706.4, UPC 1002.3, UPC 706.3, IPC 706). In the first place, even if the correct fitting was used, the vertical trap arm (before sanitary tee fitting) is still incorrect.
  • The current trap is not properly protected by the vent pipe due to the design of the trap, trap arm and drainage flow. Every trap must have a vent pipe in accordance with one of the specified venting methods (UPC 1004.1, IPC 909.1, IPC 901.2.1). This vent pipe must assure air admission, circulation and emission throughout the drainage system (so that the trap seal is not subjected to a pressure differential of more than 1 inch of water column or 249 Pa) and to protect the trap seal against siphonage and against backpressure (UPC 1002.1, IPC 901.2).
 
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