I've been renovating my bath downstairs and have almost reached the re-plumbing stage. The upstairs has no toilet, but I want to be proactive in designing the vent/waste lines so that I can one day run all my plumbing that I need up there. It's all 4" cast iron and I'm considering ripping it all out and switching to a 3" PVC so that it's easier to configure. I understand that if you're going to install a toilet directly above another, you have to have an alternative vent for the 1st floor fixtures so it doesn't cause aspiration in the system. Is this correct? If I add fixtures upstairs, do I need an additional 2" vent attached to the sink drain and vented to the vent stack?

Here's a pic of what I'm thinking. Any feedback would be great.

http://hatcherydesign.com/_images/VentStackConfig.png

Hi Foulpalamont:

You were close.. but need to run a 2" vent stack parallel to the 3" waste stack as drawn in my picture below. Also note how the sink pipe picks up the tub drain.

I have also added cleanouts where they are required.

This is a true WET VENT SYSTEM... it may or may not be allowed in your area. Call a local plumbing inspector and ask him if wet venting is allowed in your area.

If not, let us know so we can draw this up in terms of individual vents for all... ;)

Wow! I can't tell you how much I appreciate the time you put into helping me with this. I understand almost everything except for the sink pipe picking up the tub drain. For clarity, the way that bath was originally plumbed was as follows:

The 2" tub drain led sink drain (as you said) and the that convergence went directly into the 4" 90º toilet drain that in turn fed into the soil pipe. But this was all done in the crawl space and below all of the fixtures. Your drawing looks as if the drain to the tub runs above the floor and meets the sink drain at about where the hot cold water supplies would be. This goes against my limited knowledge of how tubs drain under the floor. Am I taking the drawing too literally?

Drain to tub does not run above floor... although looks like it in the drawing. I was trying to stay with your drawing but still make my point.

The idea was just to visually show that the tub drain connected into the sink drain.

Let me know if need more...

MARK

Thanks. I thought I was reading into it too much. Very, very much appreciated.

As far as wet venting goes, is the reason why some districts—in my case Virginia—don't allow it because of freezing?

You know... wet venting is a debate even amongst plumbers. In my opinion, it is most logical plumbing system...

But, if you plan on say, using your sink and flushing toilet at same time vent can be hindered and won't create the turbulent flow needed for self-scouring of system drain pipes. That being said, I still think this is best system for most average homes. As soon as we start to get into bigger homes with multiple bathrooms then I kind of split the difference and wet vent where my code says I can but also individually vent as seems appropriate.

Anyway, if allowed in your area... use this system as it will work just fine!

MARK

Thanks again. If you ever have in graphic design/computer questions, let me know!
Brian

Deal! Pop back with questions anytime!

MARK