Basement rough in question

[Giants_fan_in_PA]

I'm trying to understand this rough in. This was done as part of new construction. I had no say in what was done. I have before and after concrete pour pictures. It looks like there isn't a p-trap where the shower is connected. Is this normal? Do I have to dig it up?

Am I wrong in what I'm seeing?

Thanks.

 

[wwhitney]

My understanding (no direct experience) is that the graveled block-out in the slab is there for you to excavate to get to the shower trap arm under the slab. That lets you fine tune the exact trap and riser location to fit your shower layout. [Although it seems quite close to the foundation wall, so I guess it's set up for a linear drain at the edge of the shower, rather than a central drain.]

Cheers, Wayne

 

[Sponsor]

 

[Jeff H Young]

dig down and see if there is a trap or not. I often leave trap off so that I can dial in precise location after walls are framed etc.

 

[Giants_fan_in_PA]

dig down and see if there is a trap or not. I often leave trap off so that I can dial in precice location after waslls are framed etc.

Great comment. Thanks. I had to fight the Ryan Homes GC to put in the box. He was going to pour the concrete up to the pipe. As you can see from the first picture, there isn't a trap. Honestly, how could the pro allow that to happen?

 

[Giants_fan_in_PA]

OK. I've dug it out. Here's a picture. I've taped and drawn a circle where the drain goes into the shower pan. I need to install the P-trap. I plan on extending the horizontal 2" line into the top left corner and adding a 90 elbow going vertical a couple of inches. Another 90 going horizontally towards the lower left corner and the P-trap above the original rough in into the base. I think that'll satisfy the 4 inches I need before heading down. Thoughts?

 

[wwhitney]

The p-trap outlet elevation needs to match the side inlet elevation on the horizontal wye, other than the 1/4" per foot slope between them. I.e. you'll be digging out a little deeper to put the u-bend of the p-trap lower.

Cheers, Wayne

 

[Giants_fan_in_PA]

The p-trap outlet elevation needs to match the side inlet elevation on the horizontal wye, other than the 1/4" per foot slope between them. I.e. you'll be digging out a little deeper to put the u-bend of the p-trap lower.

Cheers, Wayne

What is the reason for the trap being on the same elevation on the wye? What is preventing it being above the wye so the shower drains directly into the p-trap?

 

[wwhitney]

The wye is your vent (wet vent in this case). The top of the vent connection (top inside of the side branch of the wye) needs to be above the "spill level" of the trap (known as the trap weir). That ensures that the trap arm will always have air in it, so it can't fill completely and siphon your trap.

So if the p-trap and the wye conflict, your only options are to move the p-trap or the wye. It's OK to have an offset in your shower drain riser with a pair of 45s, or 22.5s if you don't need much offset.

Cheers, Wayne

 

[Giants_fan_in_PA]

OK. So I just get it right. If I put the trap directly under the drain and run 4-5 inches of pipe to a 90 down to the wye, I'm not venting properly. Correct?

P.S. Digging deeper isn't an issue. I've already gone down deep enough.

 

[wwhitney]

OK. So I just get it right. If I put the trap directly under the drain and run 4-5 inches of pipe to a 90 down to the wye, I'm not venting properly. Correct?

Correct. All of the trap arm (from the trap outlet to the horizontal wye) needs to be horizontal (more precisely, total fall no more than one pipe diameter).

Cheers, Wayne

 

[Giants_fan_in_PA]

Got it. I'll connect the p-trap to the wye and go vertical from there. I'll have to go up and another 90 going horizontal to the drain. another 90 going up through the drain connection finishes the job.

Thanks for input.

 

[wwhitney]

Are you sure that you can't use (2) 45s instead of (2) 90s? That would be better. Remember that the u-bend can be at any angle (in the plan as seen from above) and that the u-bend outlet elbow can also rotate to any angle (except the ones where the outlet would hit the u-bend).

Cheers, Wayne

 

[Giants_fan_in_PA]

I can do most anything. I've dug down deep enough to put the trap into the wye as you suggest. I just thought the drain is supposed to go directly into the trap instead of running pipe into a couple of directions before getting to the trap.

 

[wwhitney]

Yes, best case is shower drain - vertical tail piece - trap u bend - trap elbow - at least 2" of exposed horizontal pipe - wye branch inlet.

But if you can't do that because the trap would physically hit the wye, the next best case is shower drain - vertical pipe - 45 elbow (or 22.5) - piece of pipe at 45 from vertical (or 22.5) - 45 elbow (or 22.5) - vertical pipe - trap u bend etc.

I.e. 45s are better than 90s, and 22.5s are slight better than 45s.

Cheers, Wayne

 

[Giants_fan_in_PA]

In my mind, the trap is above the wye. I run 5-7 inches of pipe out out of the trap to the top left corner and then go down to a 90 m
towards towards the wye.

Correct me if I'm wrong. You're saying the trap goes to the top left corner and then I run pipe up and over and up to the drain.

 

[wwhitney]

In my mind, the trap is above the wye. I run 5-7 inches of pipe out out of the trap to the top left corner and then go down to a 90 m
towards towards the wye.

The down part is not allowed, as I have mentioned repeatedly. Wherever the p-trap ends up, the pipe from the trap outlet to the wye side inlet must all be horizontal.

Yours, Wayne

 

[Giants_fan_in_PA]

Thank you so much for the feedback. I'm not sure how to use the 45's but I'll figure it out. The one thing I am sure about is lousy job done with the rough in.

 

[wwhitney]

Say you have a level plane (like the slab, hopefully), and you mark on it your shower drain location (like you did on the tape) and the projection straight upwards of the p-trap inlet. You'd like them to coincide, then you could just use a vertical pipe to connect them.

But if you can't get them to coincide, you get them as close as you can. Say the horizontal distance between them (the two projections onto that level plane) ends up 5" (to make up a number), and say the p-trap inlet is 12" below the slab (the depth needs to be a fixed amount greater than the horizontal offset, 7" should definitely be enough extra) . Then you can use (2) 45s like this:

Below the drain is a short vertical section of pipe. Then a 45 goes on the bottom, and the outlet is no longer vertical. [Or if you are really height challenged, you could use a street 45 directly into the shower drain, if it's a solvent weld connection.] You spin the 45 so it points at the p-trap inlet. Now you need a short section of pipe (the length should be (1.414 * 5") - 3", and that formula will work as long as the result is at least 1.5" (the pipe taken up by the two hubs on the 45s), and you can change 5" to your actual measurement). Then you put the other 45 on the slanted pipe so that its outlet points down; it will be directly over the trap inlet. [And again if you are really height challenged, you could use a street 45 into the p-trap inlet.]

Cheers, Wayne

 

[Giants_fan_in_PA]

One last thing...Should I be concerned about cleaning out the trap if it isn't directly below the drain?

 

[Jeff H Young]

BTW , It could be they leave the trap off because building department (possibly) charges for the bathroom, there is a difference between your fees , I've had inspectors make me go down to building department and amend permit for minor things like a sink wasn't included .