PEX around a hindrance in a shower/tub rough in.

[cale]

https://imgur.com/a/HiFAyZV

1. I've got this fat drain pipe blocking the hot and cold pipes that feed down to the shower valve, forcing the whole rough assembly beyond the studs. I am going to switch to PEX and run them behind the fat pipe to fix this. Is this ok and if so do I need to insulate the PEX at the point where it’ll touch the fat pipe? any other considerations? The fat pipe is metal, and I'm in a condo so it's shared (I didn't do the couplings, this is what I found in the wall)
   
   
2. Since I want to replace the copper pipes with PEX, I need to cut them and solder/crimp the transition. Water is fed from above via 3/4 pipe which has a point of solder to a 1/2 pipe. So should I cut the pipes above the point of soldering, on the 3/4 pipe, or do I cut the pipes below the soldering on the 1/2 pipe.

 

[Terry]

The 2" cast iron is your toilet venting, or perhaps for the floor below venting.

Most all tub valve need 1/2" supplies. I would just use the 1/2" copper lines and not bother going higher to where they are 3/4".
What you have in the wall is the old Moen Chateau with stops. Make sure your new valve also has stops.
Current code requires pressure balancing or thermostatic valves to control and prevent scalding in the shower.
Please don't get the box store Delta which is really a Peerless, those are fairly recent and I find them to be really hard to adjust the settings.
The Delta R10000 rough is better with that brand.
Kohler and Moen also make good valves.

Get rid of the Sharkbite in the wall.

The pipe to the tub spout needs to be copper, no PEX there or it will push water upward to the shower head while filling the tub.

 

[Sponsor]

 

[cale]

Thanks Terry you're the man! I really appreciate you taking the time to look at my post. People were telling me I had to deal with these metal vent pipes but since I'm in a condo I really can't do anything about that for now, especially since I'm DIY, and I doubt the HOA would like me messing with shared aspects of the plumbing. You think the couplings are alright for the vent pipe in here?

The valve I bought actually just yesterday is this one: https://www.build.com/delta-r10000-pft-px/s1573427?uid=3754542. I think it has the pressure control you mention, but not sure if the stops are in the body? It has the tub spout copper pipe so I think I'm square there.

I also read about sharkbites being a bad idea in the wall, and that was the first thing that caught my eye!

So my conclusion from your response, and let me know if I'm off here, is that it'd be alright to cut the copper pipe at 1/2", below the soldered transition from the 3/4 supply line, and there I can solder in the PEX sweat to 1/2" as well. So I wanna go PEX in order to put it behind that vent pipe instead of in front. How it is now, the rough in valve and pipes are pushed out beyond the studs. Alternative would be to keep the PEX in front of the pipe, but build out the wall a bit. Part of me wants to do this just to give the studs better support, since that vent pipe has taken big ole chunks out of them and are wobbly. What do you think would work best here?

Thank you so much Terry!

 

[cale]

Also thank you so much for that diagram! Puts things into perspective for me. One other bizarre thing for me is that I can see the back of my neighbor's fiberglass shower. Is it alright to plop in some fiberglass insulation around these copper pipes and toilet vent pipe or is that a code no go?

 

[Terry]

What you have is no-hub cast iron pipe and fittings. Those are the correct couplings for that. And no, don't change the waste and vents in the wall. That needs to stay.

Delta makes that some valve with the stops.

 

[wwhitney]

One other bizarre thing for me is that I can see the back of my neighbor's fiberglass shower. Is it alright to plop in some fiberglass insulation around these copper pipes and toilet vent pipe or is that a code no go?

It certainly wouldn't hurt, and using mineral wool might be even better, although harder to do.

The relevant questions, though, are what level of fire separation was required when your building was built, what (presumably higher) level would be required today, and are you doing anything that would trigger a need to meet today's requirements? I don't know have any idea what the answers to those questions are. But I think you should at least meet the level required at the time the building was built, even if the existing conditions don't meet that.

Cheers, Wayne

 

[cale]

Thanks for catching that Terry! I've cancelled the former, and added the valve with stops to the order. Big thank you on that.

And thanks Wayne, definitely some good questions. I was very surprised that there was nothing between our units, just some grayish insulation in parts. I wonder if just stapling insulation between the studs, behind my pipes but on my side of the wall, would be alright. I'm not sure where best to find the answers, or to know the right questions. You definitely got me thinking.

 

[cale]

Sorry last Q.. Can the PEX touch the cast iron vent pipe, or should slide on some foam sleeves or something to create some separation?

 

[Terry]

PEX can touch, not touching is always better though.

 

[Jadnashua]

More modern multi-family dwellings usually call for a fire stop between units, and a sound isolation wall is a nice upgrade...yours has neither. Fiberglass isn't all that great of a sound isolator, but mineral wool is better, but fiberglass hold together easier sometimes...denser packing can help.

 

[cale]

More modern multi-family dwellings usually call for a fire stop between units, and a sound isolation wall is a nice upgrade...yours has neither. Fiberglass isn't all that great of a sound isolator, but mineral wool is better, but fiberglass hold together easier sometimes...denser packing can help.

How about some R-tech moisture resistent foam board?