2" Shower drain into smaller cast iron pipe

[Zayd]

Hello, folks.

I've learned a lot referencing this forum through the years (as well as johnbridge.com for tiling expertise) and appreciate the time you experts give for DIYers like myself. I finally encountered a problem that I couldn't find in the archives, so I registered and here I am.

I am renovating an older (c 1951) bathroom and going from tub to a curbless standing shower with a single shower head/handheld. The tub had 1.5" drain pipe (with a 1.25" p-trap... one of many things I've had to correct from the previous owner's sins). I've pulled the tub and restructured the floor to accommodate the curbless pitch. I know that 2" drain pipe is generally recommended (and often required) for showers. I live in Michigan, which according to my research has adopted the IPC. My reading of the IPC suggests that a shower requires a minimum 1.5" drain pipe. I planned to go 2" anyway, especially with my vent stack only about 3 feet from the drain and fairly easy to access.

The question is this: would there be benefit in going 2" p-trap/drain line to a cast iron stub that is smaller anyway? Hopefully the attached pic can give an idea of sizing. The current line is the previous owner's handiwork and is 1.5".

I'd appreciate the guidance.

zayd

 

[Jadnashua]

Some codes will allow a 1.5" shower drain, some won't. Functionally, if you aren't planning multiple shower heads, it probably won't be an issue, but with a curbless shower, you really cannot afford it not flowing properly.

They broke at least a few plumbing rules:
- drain pipes cannot be necked down into a smaller pipe
- that rubber sleeve is not approved for use above ground - it requires a banded coupling to ensure the ends stay aligned.

What's above where the line gets into the drain now? Ideally, you'd replace that CI piece with a wye with the proper sized leg off of it. It appears that the threaded fitting into it now is probably 1.5" which can't be expanded to fit a 2" fitting, which is why it would be best to replace that piece.

 

[Sponsor]

 

[Zayd]

Thanks, Jim. To answer your question, the shower drain is the highest drain connection on the vent stack. There is one more vent connection coming from the basement that connects higher than the shower, then the stack exits out the roof. The other CI pipe in the background is the toilet and the PVC coming in from behind is the sink.

I am tempted to leave the shower drain at 1.5" to save me from other troubles of switching to 2", but I know that I will not sleep well if I don't. I've never tampered with lead/oakum connections and wouldn't try either, so I may call in a pro to take out that section and install a proper wye.

Another possibility: could I expand the actual 1.5" inlet in the CI? Reaming it to 2" and tapping seems it could be an option if there is enough meat in the boss. But if it's not an accepted solution by pros, I'll avoid it.

zayd

 

[Jadnashua]

I've taken out some CI and replaced it with pvc, but I've not tried to install new CI with leading it. A possibility if you did want to replace that with CI verses pvc might be to use hubless CI. You'd have to cut off the hub(s) of the remaining pieces you impact, but then, other than getting the new parts sized properly, everything goes back together with special banded clamps verses leaded connections. There are some plumbers who still work with leaded connections...it's becoming a lost art as it takes longer, and today, speed is the preference. That's one reason why they came out with hubless CI bits...they go together lots faster with less skill required. FWIW, CI is still the premium drain line...fireproof, doesn't sag or bend, much quieter as it muffles the drainage going through it. You tend to only see it in higher end homes and taller buildings these days.

 

[Zayd]

Well CI would be nice, but I'm not married to it. I've researched PVC replacement and feel it's reasonable to take on as a DIYer -- especially given the ease of access. Bracing the upstream pipe should be straightforward and it looks like there are a few different methods of cutting the pipe. I'm leaning towards a special blade in a reciprocating saw to mitigate any risk of crushing the pipe with the strap cutters.

I'll report back with results within a couple of days. Thank you again for the guidance.

zayd

 

[Zayd]

Jim -- wanted to bring this back full circle for anyone with a similar problem. I ended up cutting out a section of the CI stack and splicing in a PVC fitting with a couple of banded couplings.

It was an easier process than I expected. I used a diamond encrusted reciprocating saw blade to make the cuts. Slow going, but not unbearable -- maybe 10 minutes per cut. Even with water lubricating the cuts, I did notice that the blade was considerably slower on the second cut, but it eventually got through.

It passed a leak test and I buttoned up the floor the same day. Thanks again for the help, Jim!

 

[Jadnashua]

Glad it worked out well for you.