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Help with new drain/vent/waste system

1537 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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I know what you're going through. My wife and I built our log home almost entirely by ourselves. Lived in our RV on the property for over two years while doing it. If you don't already have them, I highly recommended a couple of Code-Check books. There's one for plumbing and one for electrical. Maybe framing and structure too, but I didn't buy that one. The actual codes themselves are nearly incomprehensible to most non-professionals.

When I started laying out the DWV system, it soon became clear that proper venting was a total mystery to me. The applicable code at the time (2008) was IRC 2003, which approaches venting entirely differently from the UPC, which I was moderately familiar with. So what I did was pay a licensed plumber a few bucks to design what I needed and I put it in.
Don't be too sure. Log homes are different. I actually think mine is seriously over-engineered. The floor joists are 2x12 at 16 oc for a 14-ft span. And those for the second floor are 4x10 beams at 24 oc, same span. But those are exposed, and more for looks than structure.
If your house was indeed plumbed by a licensed plumber and passed inspection, you have a clog somewhere. Probably in your main sewer line.

As for the lack of comments, please understand that the IRC is used in far fewer places in the U.S. than the UPC, so correspondingly fewer plumbers know it. And in some respects, the two codes are quite different. I'll repeat my earlier suggestion that you pick up a Code-Check book for plumbing. It covers both codes and has lots of useful illustrations.
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