ABS/PVC to Cast Iron question/waste stack question

Hello, a (hopefully) quick question. I'm planning on replacing the main waste/vent stack and associated vent and drain piping at my house in Seattle. The current stack is 4-inch cast iron, and my plan was to replace all of it down to the hub coming out of the foundation with 3" ABS and use a Fernco (or equivalent) donut at the junction of the CI and ABS. The issues is that I relayed my plan to my brother-in-law who's a plumber out east and he said that the first three joints in the waste stack need to be leaded. I looked through the code (International Plumbing Code 2009...I think there's a newer version, but couldn't find it online) and couldn't find anything like that. It could be that the three-joint thing is a local code that he has to follow. I guess I can see the logic in having a very tight seal at the entrance to the building sewer. If the three-joint rule is real, then conceivably I could cut the CI higher up, above the first three joints and join it with a Fernco coupler, but that doesn't seem like a better joint than the donut. Or, I could use a manhoff fitting to transition from the CI to the ABS (do they make ABS manhoffs? I've only been able to find PVC ones...) at one of the CI hubs.

Anyway, I guess the big question is: can I just transition from CI to ABS at the first hub out of the foundation using a donut or manhoff, or do I need to go three leaded joints up (seems arbitrary) then transition?

Thanks!

There is no requirement in Seattle to maintain three joints.
We're under UPC plumbing code.

Great, thanks Terry! What about the ABS-to-CI hub connection? I guess I was reading the IPC (rather than the UPC) and it looks like a donut would be allowed as long as it conforms to ASTM C 564 (thought I have to admit the phrasing of the requirement in the code is a little unclear), but it doesn't seem like Fernco makes reducing donuts (i.e. 4" to 3" since I want to put my new 3" ABS into the existing 4" CI hub) that meet this standard. They do make single-size ones, so I guess I could do 4" ABS into the donut/gasket, then put a reducer to 3" on top of that, but that seems kind silly...though not a big deal...

Upon further review (this time of the UPC) it doesn't look like there's a standard for the donut, so it looks like I can just go straight in to the hub with 3" ABS using a 4" to 3" donut. (I think...)

Cast Iron hubs in Seattle can be three different sizes.
I like to use the 4x4 inside hub Fernco, I pick up all the sizes while I'm there so that I don't waste trips.
I would consider installing a 4" santee with cleanout and then reducing on the top of that with a 4x3 flush bush.

Sounds good, thanks very much Terry!

It would be very "difficult" to follow the "3 leaded joints" requirement if the entire system was No-Hub cast iron.

Yeah, I'm not sure how that works...and in fairness to my BIL, he hasn't seen the current configuration and I might not have explained it super clearly...

At what point does the drain above switch over to 3"? You cannot go from 4" to 3" along the flow line...you can only go the same size or bigger as it flows down. THere's also the issue of fixture units in the house, which would decide the size of the drain pipe. You may be fine with 3", but if it is 4" above, you need to maintain it at 4" unless I'm missing something. IOW, you cannot insert a section of smaller pipe in the middle of a run.

The 4" would be at the end of the pipe right before it goes into the CI sewer, so the flow would start in a 3" pipe and expand to a 4". Right now the vent stack is 4", but I can size it down to 3" per code (less than 24 DFUs), so I'm going to take out all the metal piping above the slab (well, not all of it, just down to the last CI hub that's about 8" above the slab) and replace with 3" ABS. The issue Terry and I were discussing was that transition to the 4" CI hub. I was thinking of using a 4" OD/3" ID donut, which I think would work per the UBC (though, I was originally looking at the IBC and it would be tougher to use such a donut under IBC because it has to conform to a certain ASTM standard, and I was having trouble finding a reducing donut like that that met the standard).

stencil said:

Right now the vent stack is 4", but I can size it down to 3" per code (less than 24 DFUs), so I'm going to take out all the metal piping above the slab (well, not all of it, just down to the last CI hub that's about 8" above the slab) and replace with 3" ABS.

Click to expand...

You can have vent pipes get bigger on the way up just as you can have sewer pipes that get bigger on their way down. You might as well keep as much as that 4 inch cast iron vent that is supported well.

I suppose that's not a bad idea, it would keep me from having to put a 3" to 4" transition at the top to match with the roof-top vent...what kind of coupling does one need for an ABS to CI vent though? just your basic Fernco flexible coupling? Or does one need to use a no-hub (do they make reducing no-hubs? Seems unlikely...).

It depends on where you are cutting and then splicing in the plastic pipe...if above it, it is only a vent, then it would seem 3" would be fine. But, if there are ANY drains going into that pipe above, then you cannot reduce it to 3" in the middle of the run. IOW, if ANY of the drains above the point you are going to change are 4", it has to stay 4". Above ground, any couplers must be rigid. So, you'd need a banded coupler to go from the CI to the ABS. If you need to reduce it, you may need a short chunk of 4" abs, a reducing coupler and then continue on with the 3". Attaching the 4" chunk with a nohub or banded coupler. THe unreinforced couplers are only allowed underground where the two ends of the pipe will be supported by backfill, otherwise, above ground, they could become offset.

Before you cut any CI pipe out, make sure what you have above you is well anchored with approved clamps to something sturdy.

Ok, that's pretty much what I was thinking, thanks! The 4" CI that I leave in place will be well above any horizontal drain or vent inlets, it would just be the top of the stack going up through the roof. BTW: apparently here in Seattle vertical pipe needs to be supported every 4 feet (do I have that right?)...if so, what do folk use to support ABS or PVC? It seems like all the riser clamps I can find are metal, and I assume that's not compatible...