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Help with new drain/vent/waste system

1534 Views 13 Replies 5 Participants Last post by  MushCreek
I'm currently building my own house (HEAVY into DIY!) and have a few DVW questions. Mostly, I'm having trouble trying to figure out where to put clean-outs. According to the books, you should have one on the high end of every horizontal run. That will be a lot of clean-outs! What about areas where it's hard to fit one in? I have a 3" run draining two toilets that I would like to run through the floor joists. The problem comes with the clean-out. They call for 18" of clearance for a 3" clean-out, but the joists are only 16" apart. Can I drill a hole in the next joist for access? Theoretically, it's more than 18" clearance, but you'd have to bend the snake up between the joists. I'm not sure if an inspector would buy that. The only other option for this run would be to drop the 3" run below the joists- something I'd rather not do with an eye to finishing the basement someday.

The next issue is 3 fixtures in close proximity- a washing machine standpipe, a lavatory, and a shower. According to the charts, that's too much for a 2" drain. Should I combine them into a single 3" pipe, or run two separate 2" pipes?

Lastly- Does it matter whether a vent is 'upstream' or 'downstream' of a fixture? For example, I want to put the vent for a toilet in the wall behind it. This is 15" downstream, towards the main drain. It would be nearly impossible to place it upstream of the toilet. I don't think it matters, but can't find any reference to this.

Any help on these questions would be most appreciated. This all looked easy at first, but is quickly becoming complex. Our local inspectors aren't very helpful (or strict) but I want it to function well. Thanks!
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Here's a sketch of the area in question. The horizontal section of 3" is the one that could run through the joists, if I can fit it in. The branch going up in the pic services the washer standpipe, the lavatory, and the shower. I transitioned to 3", as 2" is not enough for the three fixtures (I don't think). The vent locations shown are laid out to fit interior walls. I can run a vent up an exterior wall, but the house is ICF, which means cutting a channel in the foam. 'WC' is a toilet, 'V' is a vent. The little arrows show proposed clean-outs.The funky 45 degree angles on the left are to work around a wall, and is under the stairwell. The main line with the two toilets would run through the joists or just under them, then drop down about 5', with the elbow having a 2" outlet for a vent, and then transition back to horizontal through the 45 degree angle, and then back in line with the main stack through another 45. I don't think I'll have enough space in the joists anyway, as I have the 3" branch coming in, which also has to have enough drop. The main 3" is about 12' long, and the 3" branch is about 8' long.

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We're under IRC 2006. The joists are TJI's, and I would have enough room to drill them for 3" PVC. That being said, I don't think they are tall enough to allow for the amount of pitch I need.

The venting is a puzzle. I have a code help book, and 2 other plumbing books, and they are very non-specific about where the vents need to be. They say how far away they can be (all 3 books differ on this) but they don't say where they must be in relation to the fixture. What is wrong with the venting? The toilet ones are both downstream of the fixture- should they be upstream instead? If so, I will have to branch off of the main line, and tunnel them up through the ICF foam. As shown, they are all well within the required distance. I have seen diagrams of both upstream and downstream locations for vents.
Something more like this? The drain next to the lav is the washing machine standpipe; I don't think they need to be vented as it's open to the atmosphere. I don't think the lav next to the main stack needs a separate vent(?)

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No further comment? If I wanted to hire a plumber, I would have- this is a DIY forum. My current fairly new house was plumbed by a professional. The master lavatory drain is so high in the wall that it barely drains, and clogs easily due to slow flow. When you run the washing machine, it bubbles up in the master toilet, sometimes with soapy water. If you flush the toilet during the wrong part of the cycle, the toilet will back up and over flow. I'd like to think I can do better than that. I can't tell what they did wrong without tearing out the drywall, so I'm going to focus on my new house. I'm still looking for feedback- Thanks!
An update- I continued my research, and believe I have a valid design now. I had to re-work the shower to get it right. In the course of my research, I found out that the under slab plumbing that was done by a professional is wrong, but will probably work OK. It is for a basement bathroom that will rarely be used. I wish I knew more about this before I signed off on the work and buried it under concrete. The inspector didn't catch it, either. My two experiences with professional plumbers have been 0 for 2. That explains part of why I'm building my own house.
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