DWV design help

[JoeNotThePlumber]

Hello,

I am not a plumber but a fairly experienced DIYer. I am currently remodeling a second story bathroom in my 100 year old foursquare in Michigan. I have completely gutted the thing and am beginning to put it back together. I need a bit of advice and input on the waste lines and vents. I will try to keep this organized as clearly as I can.



How it is now:

The cast iron stack is directly behind the toilet. Toilet sat on a closet bend with a side inlet on either side. The lav drains into one side and the tub into the other. Neither the tub nor lav have a vent. It is just 1.5” galvanized pipe from the trap to the inlet under the toilet. The tub used a canister trap, the lav a modern P-trap.

In the basement a previous owner removed the cast iron stack from the basement floor up to the basement ceiling. There is now PVC to the floor and a 3” branch that serves 1st floor powder room. The iron stack runs up the first floor wall with no connections on the first floor at all.

What I am setting out to accomplish:

Bring this up to modern standards to avoid waste water coming through the ceiling(again).
Add hook-ups for laundry machines in the very large hallway closet.

My plan:

I will remove the cast iron stack in the wall I have exposed (second floor and attic).
I will run 4” PVC from the basement all the way to the roof.
I will plug the top and bottom of the old stack and just leave it in the wall. There is plenty of room in the wall cavity and moving the toilet over 6” does not bother me. I do not want to tear up the first floor walls to remove it.
The toilet will drain directly into the new stack.
The only other connections to this stack are an existing vent, a vent in the attic I will add and a 2” PVC pipe that I will describe below.

This pipe will start 4 feet off the floor were it will connect to the new stack. It will run behind the lav and down into the floor. It will travel across the floor turn 90 degrees and down to the basement where it will connect back to the stack.

This pipe will drain the lav, laundry drain, and tub and vent the lav and tub. I will run a vent for the laundry trap up into the attic and connect it to the new PVC vent stack.

There is a drywall soffit/column on the first floor below the bathroom that I can run the 2” pipe in.

Questions:

1. Any issue abandoning the cast iron in the wall? (at least until there is another reason to tear into the first floor walls)

2. Does my design make sense? I thought of coming across the floor in front of the toilet and draining everything down the main stack rather than down the soffit to the basement. I thought avoiding the big notches in the joists was a good thing since the laundry and tub will need 2” pipe. By the time I account for .25"/foot of drop the notches will be way to deep.

3. I was going to add cleanouts under the lav and below laundry trap. Any place else? Most of this will be completely covered by wall tile and floor so my options for clean outs are limited.

Thanks in advance!

 

[JoeNotThePlumber]

 

[Sponsor]

 

[Terry]

That should work, the lav is wet venting the shower and the washer is downstream of all of that and has it's own vent.
When going through joists, no more than a 1/3 and leave 2" at the top and bottom of the joist. Which for me means no 2" if it's a 2x8 or smaller.
I would rather fir down the ceiling downstairs for that. A 2" pipe being almost 2.5" would have to be dead center of a 2x8 and getting grade would be an issue.

 

[JoeNotThePlumber]

Thank you Terry. The joists are 2X8. Previous handymen had hacked away at them over the century since the house was built to the point that some were effectively 2X3s. I sistered new lumber on them and also corrected the fact that it was 1" out of level across where the tub will be installed. I was not keen on taking Sawzall to that work.

Any comments on cleanouts?
What about suds from the washing machine? Is the long drop and issue for that?
Is the wye where the laundry ties in vertically the correct fitting? Somebody had suggested a sanitary tee .

What about abandoning the cast iron in the wall?

 

[Terry]

Some codes like a 3" where the washer ties in. In Washington State they don't require that.
The washer p-trap trap arm goes into a santee, but downstream you can enter the line using the wye. You have the option of using a santee on the vertical.

 

[JoeNotThePlumber]

Thanks again for the advise. Today I got most of this plumbed but I stopped at replacing the stack. It is going to be very difficult to run the 4" PVC up the wall without tearing up walls on the first floor. 3" will be no problem though. Since this is only draining the toilet I am thinking 3" should be ok. Every vent ties in above the toilet and the kitchen and powder room get thier own vent on the other side of the house.

I am wondering why it was originally plumbed with 4" cast iron from the basement floor all the way up to the roof just for a toilet, lav and tub. Was this just the customary way it was done 100 years ago?

 

[Michael Young]

Thanks again for the advise. Today I got most of this plumbed but I stopped at replacing the stack. It is going to be very difficult to run the 4" PVC up the wall without tearing up walls on the first floor. 3" will be no problem though. Since this is only draining the toilet I am thinking 3" should be ok. Every vent ties in above the toilet and the kitchen and powder room get thier own vent on the other side of the house.

I am wondering why it was originally plumbed with 4" cast iron from the basement floor all the way up to the roof just for a toilet, lav and tub. Was this just the customary way it was done 100 years ago?

Your vent ONLY HAS TO BE HALF THE DIAMETER of the pipe it serves. If you already have 4" cast iron, get up on the roof and slide a 20' piece of 2" or 3" pipe THROUGH the old case iron. just ue that old 4" CI as a chase to run your vent. I'm pretty sure 3" PVC will slide freely through 4" cast iron.

 

[JoeNotThePlumber]

Your vent ONLY HAS TO BE HALF THE DIAMETER of the pipe it serves. If you already have 4" cast iron, get up on the roof and slide a 20' piece of 2" or 3" pipe THROUGH the old case iron. just ue that old 4" CI as a chase to run your vent. I'm pretty sure 3" PVC will slide freely through 4" cast iron.

Thanks for the reply. That is not a bad idea. it wont work in my case though. The 4" iron pipe turns almost 90 degrees in the attic the goes vertically trough the roof a few feet over. I think this was done to avoid the aesthetic problem of the pipe sticking 2' out of a dormer roof. it penetrates in a large area of the hip roof where it is much less conspicuous. I plan to go into the attic and over with 3" PVC like the cast pipe does. I'll leave the well supported cast iron elbow and the part that penetrates the roof and connect the 3" PVC to it with a reducing coupler and shielded rubber coupling. If I have some other reason to be on the roof in the spring I will change the flashing and run the PVC the rest of way.