Removing old cast and installing PVC , existing back to back with double 90 ??

[FishingDave]

Hi I am removing the old cast iron and installing a new PVC . I have two toilets that are back to back on a double 90 on the horizontal to a 3" pipe that runs horizontal about 2ft and connects to the main vertical stack. My question is can I install a double wye fixture(or double wye with 45) horizontal in place of the double 90 ? And do I need to vent it even though its only 2 feet away from the stack??

 

[wwhitney]

It would be easier to understand your configuration with a diagram. What's connected to the stack above the WCs, and anything drain into the stack from a story above the WCs?

Cheers, Wayne

 

[Sponsor]

 

[Terry]

A bathroom or multiple of them would need venting before entering a waste stack from above.

A double wye works, but it needs to be vented before the waste stack.

 

[FishingDave]

Here is the way it is now

 

[wwhitney]

I assume in your drawing, up and down the page is vertical, except for the "double 90" and upstream WC fixture drains, which actually are horizontal and run in and out of the page.

A flat double 90 is not a good geometry, as even with the outlet sloped at 2%, each inlet will be level with no slope. For that connectivity a wye is called for.

But with the lavs on the stack above, you have a vertical wet vent. And the IPC calls for each wet vented fixture to connect to the stack "independently." https://up.codes/viewer/connecticut/ipc-2015/chapter/9/vents#912.1.1

So you'll either need to figure out how to connect the WCs to the stack with an upright double wye (as WCs are required to connect at the same elevation), or add a revent (a dry vent that comes off the fixture drain before the stack and then reconnects to the stack at least 6" above the lavs). The revent would let you use a single 3" drain connection to the stack, with a horizontal wye to combine the fixture drains. And the revent could be between one WC and the wye (thereby dry venting that WC and letting it wet vent the other WC) or between the wye and the stack (as the IPC allows common venting in that configuration).

Cheers, Wayne

 

[FishingDave]

Would this work? Double Wye 3" horizontal then hook up at vent line above the sink lines? The Two sinks are back to back off the same 3" line I was going use a a double fixture wye tee

 

[wwhitney]

No, the vent takeoff can't be horizontal, the vent has to come off vertical (at least 45 degrees above true horizontal) and stay vertical until at least 6" above the fixture flood rim. [And BTW, the kitchen sink's vent has to rise up to join the bath (tub?) vent at least 6" above both fixture's flood rims.]

So you could do something like below, assuming it would fit, where red is drain, green is vent, the drawing in is plan view (overhead), and vertical pipes are shown as circles (stack, vent, and two closet flanges). The vent takeoff is best done with an upright combo (rolled up to 45 off vertical) or an upright wye, but if space is tight the IPC would allow a san-tee on its back (rolled up to 45 off vertical) for the vent takeoff.

For the sinks, you need to use a double san-tee or (better, perhaps required) a double fixture fitting. A double combo (tee wye) is not appropriate for venting, and your sinks rely on the stack connection for their vents.

Cheers, Wayne

 

[Reach4]

No, the vent takeoff can't be horizontal, the vent has to come off vertical

IPC. Suppose that drawn-in toilet vent were not there. Looks good for a 2-bathroom group with the lavs venting the two toilets?

 

[wwhitney]

IPC. Suppose that drawn-in toilet vent were not there. Looks good for a 2-bathroom group with the lavs venting the two toilets?

Not with two WC drains joining each other before the stack, and with two lavs on the stack above that.

If the stack were split, with two parallel vertical segments that combine together above and below, and one lav and one WCs on each stack, that would be fine. Or if the WC drains join the stack individually, but at the same level, that would also work.

Cheers, Wayne

 

[FishingDave]

Thanks for all the advice its helping me figure it out alot. The problem the main stack is only about two feet away from where the the wye would be and the toilets a little over 14" from that. So i don't have any real room to install a vent on of the legs going to either toilets . I can install a double wye and use a long sweep at the end and pipe it up to the vent in the attic but from what your saying that's not approved. Do you always have to vent the toilet even if its under 6 feet from the main stack?

 

[wwhitney]

Yes, every WC needs a vent, the IPC allows it to be far away, but it generally needs to connect before or as any other drain joins in.

If you have the height available, the simplest option is to put a double wye with the barrel vertical in the stack, then going upstream each wye branch gets a quarter bend to turn horizontal for the 2' run to the WC (at the proper distance from the wall between the two WCs), with another quarter bend under the WC as a closet bend.

Slightly shorter, but still fairly tall, would be the upright double wye, a street quarter in the branch entry, and a street LT90 into the quarter bend. For a 4x4x3x3 reducing double wye (is the stack 4"?), I get that that configuration would put the entry to the street LT90 about 13.75" from the stack center line (along the dimension between the two back to back WCs). I think that's about right, but could be 0.5" to 1" too small, not sure if that would be a problem.

So if the upright double wye fits, that's definitely the simplest way, it lets the stack vent both WCs. If it's too tall, let me know and I'll look at the dimensions of the horizontal options I mentioned earlier.

Cheers, Wayne

 

[FishingDave]

Thanks Wayne for all the help ,I have a better idea on what to do now. I will take some pics and post it . Its a really tight space and I forgot to mention that its between two finished walls . but I might be able to do a 3" double fixture on the vertical , and then 45 that to the main stack with a Tee wye . I can run a 2" vent from the the top of the double fixture fitting up to the roof line and connect it back to the main stack for the vent . Its amazing with all these vent requirements now a days compared to what's there now lol. I will take some pics tomorrow thanks for all the help!!

 

[FishingDave]

Hi Wayne

Here's some pics on what I am dealing with.

 

[wwhitney]

Is the wall above (last picture, I presume) stacked over the wall below?

Cheers, Wayne

 

[FishingDave]

Is the wall above (last picture, I presume) stacked over the wall below?

Cheers, Wayne

Yes the last pic with the offset is the second floor. You can also see the double tee , where one side of the bathroom sink is

 

[wwhitney]

One option to consider is putting an upright 3" double wye between the two closet flanges. A street 45 to a quarter bend (or reducing closet bend) with the double wye should fit within the height of the floor framing (needs verifying). The stack above would receive the combined lavs via a single san-tee, as the IPC allows common venting. Then the stack could jog back to join the vent (if necessary). And in the story below, the drain can jog to be wherever it needs to be.

Cheers, Wayne

 

[FishingDave]

Thanks Wayne I'll see if I can make that fit. if not I might have enough room to install a vent connection ,between a double tee wye on the horizontal (connects wc) and sanitary tee at the stack. Tight but might work