Adding Shower drains - Dry Venting

[RDS1128]

I have a two story-two bath home (full bath on each floor) with a full basement (where the main drain system resides). I am remodeling the first floor bathroom. Removing the fiberglass tub/shower combo. Taking out a wall and building a walk-in shower to the other side of the new expanded bathroom (2 drains in new shower). In doing so, I have questions relative to the draining system in the basement. I hope the model below provides an understanding of what I'm trying to accomplish.
Can the current shower drain (which is vented from above be plumbed in the main drain system (pictured below)?
Can I add the 2 new drains downstream as shown below? There would be no venting directly to those drains.

 

[wwhitney]

You are showing a portion of of your building drain. Every connection to it should be a drain which has already been vented. If each of your 2 new shower drains has a vent properly connected within 2" of fall of the trap outlet before joining the building drain, no problem with the connections as shown.

Cheers, Wayne

 

[Sponsor]

 

[Reach4]

Confirm that the 3-port fittings,that you show a bunch of, are combos or wyes, and not sanitary tees. You cannot use a sanitary tee (santee) in the horizontal plane.

If you can convert the 1.5 from the kitchen to 2 inch feeding a long-sweep bend, and continue with 2 inch, will be an improvement.

 

[RDS1128]

Wwhitney - the problem I have is a cannot individually vent those drains 6" above flood before connecting. Wondering what options I have. I don't really understand what you mean by "vent properly connected within 2" of fall of the trap outlet before joining the building drain". Can I convert what I label "the existing first floor shower wet vent" (since that shower is no longer used) to dry and attach horizontally under the floor joists to the new shower drains, just above the traps?

 

[RDS1128]

This is a firsthand pic of the project. Please provide feedback on:
How to tie in the 2 new shower drains and what to do with the "existing first floor shower (wet vent)" (2nd text box down from top left) which will no longer be used as it's being replaced with the new shower (2 new shower drains).

 

[wwhitney]

Wwhitney - the problem I have is a cannot individually vent those drains 6" above flood before connecting

Why not? It's usually possible with sufficient rerouting and carpentry.

I don't really understand what you mean by "vent properly connected within 2" of fall of the trap outlet before joining the building drain".

Any trap requires a vent. That vent connection has to occur close enough to the trap. Close enough means before the trap arm has fallen one pipe diameter relative to the trap outlet. This is what allows the vent to keep the trap arm from being able to siphon the trap.

That vent connection can be a dry vent, meaning a pipe that has only air in it. Dry vents have to be taken off the upper half of the pipe, and they must rise vertically (meaning up to 45 degree off plumb) until at least 6" above the fixture flood rim. Above that elevation, dry vents may turn horizontal and may combine with other vents that are similarly at least 6" above their fixture flood rim.

Can I convert what I label "the existing first floor shower wet vent" (since that shower is no longer used) to dry and attach horizontally under the floor joists to the new shower drains, just above the traps?

No, as per the previous paragraph, dry vents may not be horizontal below an elevation of 6" above the fixture flood rim.

Why have you labeled the 1-1/2" (E) shower on the left a wet vent? A wet vent means a pipe that is acting as both a drain and a vent. Wet vents may connect horizontally to the drain being vented. An example of a wet vent is a 1-1/2" lav drain, with a 1-1/2" dry vent, that comes down and connects to say a shower drain, close enough to the trap (as described earlier).

Nothing in your picture can rely on that 3" building drain to provide venting. You could use one shower drain to wet vent the other. One shower drain gets a dry vent taken off as above, and then after that vent takeoff, that shower drain joins the other shower drain to vent it. The distance/elevation of the first shower drain between the dry vent takeoff and where it connects to the second shower drain to wet vent is not regulated.

Or you can dry vent each shower, or you can reroute the lav to wet vent the shower(s), although in that case you need to pay attention to how the WC is vented, it may be relying on the lav to wet vent it.

BTW, WI uses its own plumbing code, so unlike the IPC and UPC, I'm not familiar with the particular quirks it has and some of the sizing rules that vary across plumbing codes.

Cheers, Wayne

 

[RDS1128]

Why not? It's usually possible with sufficient rerouting and carpentry.


Any trap requires a vent. That vent connection has to occur close enough to the trap. Close enough means before the trap arm has fallen one pipe diameter relative to the trap outlet. This is what allows the vent to keep the trap arm from being able to siphon the trap.

That vent connection can be a dry vent, meaning a pipe that has only air in it. Dry vents have to be taken off the upper half of the pipe, and they must rise vertically (meaning up to 45 degree off plumb) until at least 6" above the fixture flood rim. Above that elevation, dry vents may turn horizontal and may combine with other vents that are similarly at least 6" above their fixture flood rim.


No, as per the previous paragraph, dry vents may not be horizontal below an elevation of 6" above the fixture flood rim.

I've come to that understanding but if the 1-1/2" cry vent comes vertical from the 2 story roof, then elbows below the first-floor joints and connects with the trap, because the elbow is below the 6" fixture mark this is not allowed? Just want to be sure I understand in layman's terms. Because Google states (SPS382 is WI code)
according to SPS 382, a dry vent elbow can be installed below a fixture and run horizontally, but with some restrictions. The vent must rise at least 6 inches above the fixture's flood rim before going horizontal, and a cleanout is required for horizontal vents less than 6 inches above the flood level rim.

Here's a more detailed breakdown:

• Rising before Horizontal:
  A dry vent must first rise vertically at least 6 inches above the flood level rim of the fixture it serves before it can run horizontally.
  
  
• Cleanout for Horizontal:
  If a horizontal vent is less than 6 inches above the fixture's flood rim, it requires a cleanout.
  
  

Why have you labeled the 1-1/2" (E) shower on the left a wet vent? A wet vent means a pipe that is acting as both a drain and a vent. Wet vents may connect horizontally to the drain being vented. An example of a wet vent is a 1-1/2" lav drain, with a 1-1/2" dry vent, that comes down and connects to say a shower drain, close enough to the trap (as described earlier).

The 1-1/2" (E) shower is the one being replaced by the 2 new shower vents. So what was a wet vent is now dry.

Nothing in your picture can rely on that 3" building drain to provide venting. You could use one shower drain to wet vent the other. One shower drain gets a dry vent taken off as above, and then after that vent takeoff, that shower drain joins the other shower drain to vent it. The distance/elevation of the first shower drain between the dry vent takeoff and where it connects to the second shower drain to wet vent is not regulated.

Should I connect the 1-1/2" (E) former wet vent (now dry) to the 3" main as it is?

Or you can dry vent each shower, or you can reroute the lav to wet vent the shower(s), although in that case you need to pay attention to how the WC is vented, it may be relying on the lav to wet vent it.

BTW, WI uses its own plumbing code, so unlike the IPC and UPC, I'm not familiar with the particular quirks it has and some of the sizing rules that vary across plumbing codes.

Cheers, Wayne

 

[RDS1128]

Also. at some point to dry vent a linear floor drain (one not near a wall) out 3" from the exterior of the wall, doesn't there have to be an elbow?

Wayne - I appreciate all the info you've supplied. I obviously need to be sure I get this right. Thank you!

 

[wwhitney]

I've come to that understanding but if the 1-1/2" cry vent comes vertical from the 2 story roof, then elbows below the first-floor joints and connects with the trap, because the elbow is below the 6" fixture mark this is not allowed? Just want to be sure I understand in layman's terms.

Correct. The usual way this is dealt with is to route a trap arm to a location under a wall that is "close enough" (to the trap) so that the vent can come off vertically and rise directly into the wall.

Because Google states (SPS382 is WI code)

I don't trust AI, but the reference was plausible enough that you made me go check SPS382:

383.31(15) VENT GRADES AND CONNECTIONS. (a) Vent grade. All vent and branch vent pipes shall be graded and connected so as to drain back to a drain pipe by means of gravity.
(b) Installation. Vents shall be installed in accordance with subds. 1. to 3.
1. Except for wet vent piping, the connection of a vent to horizontal drain piping shall be at a point above the horizontal center
line of the drain piping.
2. Except as provided in subs. (12) and (17), vent piping serving a wall-outlet fixture may not offset horizontally less than 36" above the floor, but in no case lower than the elevation of the highest flood level rim of any fixture served by the vent.
3. Vent piping may not connect to a branch vent less than 38" above the floor, but in no case lower than 2" above the elevation
of the highest flood level rim of any fixture served by the vent.

So WI has deviated from the 6" above the fixture flood rim rule I quoted you from the IPC/UPC. I didn't find anything like what the AI said, but the Appendix does have the illustration below for 381.31(15)(b). Apparently you can jog your shower dry vent horizontally below the floor, WI is unusual in that regard. Still better to minimize such jogs by carefully routing of the trap arms.

The 1-1/2" (E) shower is the one being replaced by the 2 new shower vents. So what was a wet vent is now dry.

I don't believe that the pipe in the left-hand picture you have labeled as a wet vent is in fact a wet vent. If that shower drain went on to connect to say another shower trap arm (whose trap would have to be much lower, since the pipe is vertical coming out of the bottom of a san-tee), and that other shower trap arm relied on that drain to provide a vent, that would a wet vent. But if I understand your existing configuration, the shower drain is just shower drain.

Cheers, Wayne

 

[John Gayewski]

Just to add. If your going to run a dry vent under the floor horizontally, at some point that vent will likley need cleaned out. Make sure to have a cleanout access in your vent pipe.

A lot of people run vents like this even though it's mostly not legal. I've learned to be fine with it but there should be access to clean it out in the future in the event that thr tap starts being siphoned due to blockage in the future.