Multilevel toilet DWV design

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roundrightfarm

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Greetings everyone,
I am getting ready to install a DWV system for new construction. 5 toilets total will be run through 2 DWV sub-systems that connect under the basement slab before exiting the house to the septic drain.

One DWV subsystem has three toilets. These are on the first floor, second floor and finished attic, and will all share a 3" drain stack, which will combo wye into a 4" drain, running horizontally in the first floor joists (first floor toilet has a 4" drain). This drain then drops through the basement to the septic drain.

I live in an area with no building codes, but If I understand good DWV design, I should not wet vent the first and second floor toilets through the soil stack because they have toilets above them.

question #1. For my first and second floor toilets, should I use a sanitary tee as a closet bend, which would then serve as a vent out the uphill end? If so, do I need to get vertical before reducing to a 2" vent, or can i do this immediately while still horizontal?

question #2. Since the attic is finished, there is not a lot of room to connect vents without going through the load bearing exterior walls. For a 2" pipe, the hole I would have to drill would be more than 40% of the 2x6 studs. Consequently, this house will have 4 or 5 roof penetrations for vents. I'm considering venting though the attic exterior walls rather than through the roof, since we also live in heavy snow country where ice dams can tear off roof vents.

I read a code that says you should not do this where the roof soffit is vented. Ours will be. Will this be a problem with a finished attic that is closed to the under-roof air space? is it ok for sewer gases to be under the roof line, especially after they have mixed with outside air?

Thanks for your advice
 

Cacher_Chick

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Fixture vents are downstream of the fixture's trap. No part of a dry vent can be horizontal until it is at least 42" above the floor.
The vents can normally be routed so they are at or above the upper half of the roof deck to avoid problems with ice on the roof.
 

roundrightfarm

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You CAN'T use a sanitary tee for a closet bend and vent, but this is too extensive a project to even try to design it using the Internet.
What is the typical way of doing this. Can a closet bend be part of a tee, so that venting can be done the opposite direction from drainage? If I use a combo wye, I'm afraid I would lose too much vertical to properly slope the horizontal drain before running out of room with the 2x10 joists.

thanks
 

Terry

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Wye off downstream of the toilet, with a wye. Thinking you can stack it vertical is wasting time. Nobody plumbs them in that way that knows what they are doing.
I've cut plumbing out where someone has installed a santee on it's back to pick up a toilet, and the solid waste drops down and spreads out both directions, blocking the uphill section.

Normally on a horizontal, you wye off for fixtures. Those wyes my be vertical, or they may be horiztonal. In a slab, they are mainly horiztonal. Before the fixture enters that main line, you pull a vent off.

I don't care if you have inspections or not. They don't in third world countries either, it most places I stay at smell very bad. Their excuse is that they don't have anyone making them do it right. And yes, you can tell.

dwv_b1.jpg


http://www.morgantownwv.gov/government/city-government/code-enforcement/
 
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WJcandee

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From your questions, we can tell that you need to educate yourself before even thinking about doing this. Just because you can go to ACE and buy all the parts without a license doeesn't mean that you can assemble them in a way that's safe.

Read these two guides, cover to cover, and understand them. That should help put you in a better position to converse intelligently with our experts.

http://www.klickitatcounty.org/documentcenter/view/103

Helpful Plumbing Hints for Residential Construction by Bert Polk Plumbing Inspector Lincoln County
 
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roundrightfarm

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Thanks for the help. I only mention that I have no building codes because a common response in these forums is that it depends on the local code. Thanks also for the guides. The two above are very informative. Since I don't have the benefit of an inspector, I am studying as much as I can to help make sure I get it right and am not cursing myself as I have to redo it.

I think I need to ask a more general question that I have not seen covered in any DWV guides- Can a toilet drain into an elbow, then immediately to a combo wye, laid horizontally, and which is connected to a horizontal drainpipe, and then vented with another combo wye (now positioned vertically)? From what I have read this seems to be ok, but I have never seen a diagram of a toilet connected this way.

I am also looking for guidance on what constitutes a proper closet elbow. Is this a specially formed fitting, or can it be a medium 90 or a long sweep 90?
 
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roundrightfarm

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I've attached a couple photos of what I'm wondering will work. The toilet wye is on it side, as well as the 3" long sweep. The other bends are going vertically. I need both vents and the upper level drain to go up through the interior wall, which is lightly sketched in for the first picture. Even if the arrangement in the first picture works in theory, I still don't have the space to put the toilet vent before the long sweep. I will run in to the exterior wall, which I don't have easy access to get under, as it fully supported by 2 band joists. This is shown in the second picture. Please let me know your ideas on the second picture. Is the 180 that the toilet drain does a problem? I also need to check if this will allow me to get close enough to the wall for a 12" rough in on the toilet flange.

Thanks for your advice.

drain.jpg
drain2.jpg
 

roundrightfarm

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here is another idea, which avoids the 180 on the toilet drain, but the toilet vent looks unorthodox. Any opinions on if either will work, which is better, or a different idea would be much appreciated.

Is there such a thing as a combo wye with side inlet on the straight part. I only see them with the inlet on the curve. If it was on the straight, it would solve my problem I think

Thanks
drain3.jpg
 

Terry

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Wet venting is for a bathroom group on the same floor.
Not for running an upstairs bathroom group through the lower bathroom group.
Take your lower floor, and vent it properly "before" it ties into the waste line from above.

wet_vent_upc_back_to_back.jpg


Here is an example of a wet vented bathroom group. This can wye into other waste downstream, but you can't bring in an upstairs bath upstream of this.
 
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roundrightfarm

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Thanks Terry for your help. I've come up with an arrangement which I think fits the bill. Below is a birds eye view. Please let me know if you see any problems with it.
drain4.jpg
 
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