P-trap location problem

[davejcb]

Hello all!

This is my first post- renovating my first bathroom, need advice. Have done lots of homework, but need experienced advice.

Situation: Going from tub/shower insert to standup shower. Drain was on left side, now needs to be centered. This was the tub's drain and overflow. I then opened it some more, and then more. That last picture shows where the drain needs to go- right over the bottom joist and PB pipes, circled in pencil. Obviously, these are both in my way. The joist is sistered, by the way.

This is where I'm at. I've notched the sistered joist, and drilled the 2.5" hole for the 1.5" ABS to come through. The 1/4" / foot slope works fine through the joist.

The problem is I can't get the P-trap low enough because of the PB pipes. Since it's so high, it won't line up with the pipe coming through the hole in the joist without taking a drop of a few inches.

My solution to avoid make a drop right after the P-trap (thus making an S-trap) is to have a waste arm (of 2 times the diameter of the P-trap), then a 90* elbow down and another to meet the pipe through the joist.

This is the contraption, and this picture and this picture show how it is mocked up.

So. Is this setup crap, or will it work? Will I get siphon effect like an S-trap, or will the two 90* elbows drop cause a problem, will this flow?

Thank you for any help you can offer!

Dave Ruel

[John Kogel]

There is another way. Well, there always is, but here is my idea, and I am not a plumber, so it might get shot down. []

From the drain, go to an elbow, cross over the plumbing lines with a slight downward slope, 1/4" / ft, then put your trap so the trap arm, the exit, goes out thru that hole in the joist, horizontal to the original drain. This will let air flow back to the trap, so no siphon problem.

[Ben H]

While this is really not in your question, since you have the PB exposed already, I'd replace it in that area. Given the history of PB, you could very well have a ticking water bomb in your house. There is always a chance nothing will ever happen. But you already have it opened up, and 50 bucks worth of copper or PEX or PVC would eliminate the problem in that area. Why not?

[davejcb]

The whole house is PB... I just want to get this damn floor closed up so I can move on with this washroom

[Marc]

While this is really not in your question, since you have the PB exposed already, I'd replace it in that area. Given the history of PB, you could very well have a ticking water bomb in your house. There is always a chance nothing will ever happen. But you already have it opened up, and 50 bucks worth of copper or PEX or PVC would eliminate the problem in that area. Why not?

I don't write up PB tubing anymore, just PB fittings. Isn't the problem confined to the fittings?

Marc

[Tom Raymond]

I don't see why the trap wouldn't fit right between the PB tubing. If not, you could always just get a left or right drain shower base.

I wouldn't mess with the PB unless you plan on taking out a lot more than we can see in those pics. Systems that are prone to failure tend to fail when you start messing with them. Now that you know there is PB tubing, you need to budget for it's eventual replacement, or get really good insurance.

[davejcb]

From the drain, go to an elbow, cross over the plumbing lines with a slight downward slope, 1/4" / ft, then put your trap so the trap arm, the exit, goes out thru that hole in the joist, horizontal to the original drain. This will let air flow back to the trap, so no siphon problem.

I like it. Here and here I did a mockup of what I think you mean. Is this a better configuration? More elbows, but the trap goes into the horizontal line...

Thanks!

[John Kogel]

Yes, that gets an appproval from me, but I'm no plumber, right?

To get rid of a pesky nail that won't go away, I sometimes use a hack saw blade on them, or just grab it with vise grips and snap it off.

If you use screws for construction, they should be the expensive construction grade. Big Mike never tells us these things.

You could line those joist cavities with poly and tape, directing possible future water leaks over to the walls? Then install one of those leak alarm sensors.

[davejcb]

Mission accomplished.

Pipes are installed, and glued, and the drain lines up!

Tested it with a few liters of water, so far so good, no leaks!

Thanks for the help!

Dave

[John Kogel]

OK. I would have turned the trap so it pointed straight at the drain, but that works. If you ever get hair ball clots in your drain, you can still pull the mess out with a hook.

One more thing. If you install a fiberglass shower, make sure you support the floor so that it can't flex. We see a lot of leaky drains caused by lazy builders who don't read the instructions.

[davejcb]

Done and done. Thanks for the tip John!

[John Kogel]

OK, you have a solid floor. I mean for support of the fiberglass shower floor, a bag or bags of wet (damp) mortar stuffed in around the drain. Some units have OSB-reinforced floors, but many do not.

[davejcb]

Ah, gotcha. The base actually has leveling feet, so I need to adjust them all to get support and avoid squeaking. Here's a picture to better explain.

I've since made progress... 3/4" plywood, and a LOT of screws!