Bath Design (2012 IPC)

[readytowork]

Does anyone see a code violation with this design? My municipality uses 2012 IPC.

It's for stacked bathrooms, with lav, toilet, tub/shower + a washing machine in two-story home. Slab on grade, so the lower fittings are in the earth.

I'm proposing 1.5" fittings for everything except the main stack (3"), toilet (3" after the closet elbow), and washing machine (2").

The third photo sort of shows where the slab/footings will meet the plumbing.

 

[wwhitney]

No kitchen sink?

Your lower story bathroom venting doesn't work, at least not without looking into something exotic like Single Stack Venting. For normal venting, the lower story bathroom requires at least one dry vent that connects to a roof vent without seeing any drainage from above (or I guess it could be an AAV), typically on the lav. And then if you want to use that dry-vented lav to wet vent your shower and WC in that bathroom, the upstairs drainage needs to be kept separate from the downstairs drainage, i.e. the downstairs lav joins the downstairs shower/tub and then WC (or WC and then shower/tub), and only then does the upstairs drainage join in. So typically for stacked bathrooms, if you cut your DWV system at a plane on the first floor but near the ceiling, you'd have one 3" drain line coming down from the story above, and one vent line rising up from the story below.

A good practice is to use a minimum size of 2" under the slab, and possibly to use 2" for tubs and showers.

Cheers, Wayne

 

[Sponsor]

 

[readytowork]

This is an addition, which is why there's no kitchen. (Good observation, though.)

Based on your comments and the layout, I need to add a vent to the 1st story shower/tub and a vent to the 1st story sink, right? They are far apart on the layout, which is why I'm proposing a vent for each one. That would leave the 1st story toilet still venting through the 3" line that serves the toilet. Would that cover the venting problem that you addressed?

 

[wwhitney]

Based on your comments and the layout, I need to add a vent to the 1st story shower/tub and a vent to the 1st story sink, right? They are far apart on the layout, which is why I'm proposing a vent for each one. That would leave the 1st story toilet still venting through the 3" line that serves the toilet. Would that cover the venting problem that you addressed?

Not sure I'm following what you propose, but for standard venting, nothing on the first floor can be vented via a path that goes through a pipe carrying drainage from the second floor. What I was trying to describe is expressed at least schematically in the diagram below. There are other ways to vent things, but the schematic just shows the idea of having one vent and one drain passing between the floors, and the upstairs drain joining the downstairs bathroom group after everything in the downstairs group has been vented.

In the drawing below, the downstairs bathroom group uses wet venting via the lav, while the upstair bathroom group has everything dry vented. Either approach is fine for either bathroom; the point is that everything gets vented before any drainage gets combined between floors.

Cheers, Wayne

 

[readytowork]

Thank you. What requirements for a single stack vent are missing from my initial drawings? All of the fixtures are within 4 feet of the main drain/vent stack. Since each floor has one tub/shower, toilet, lav, each floor has 6 DFUs (for a total of 12), which I thought I could vent via a 3" stack like this. Based on what you've explained, I'm misunderstanding a concept from the code. Do you know where I can read to understand the concept your describing about nothing on the first floor being vented via a path that goes through a pipe carrying drainage from the second floor?

 

[readytowork]

I think I see now. It's because of the toilet on the 2nd floor, right? If I didn't have that, I think the stack would have worked. Thank you.

 

[wwhitney]

IPC 913 Waste Stack Vent and IPC 917 Single Stack Vent System are the more exotic options I mentioned in my first post, which you don't normally see in single family residences. IPC 913 rules out WCs, so that leaves IPC 917.

You could do a Single Stack Vent System very close to your original diagram. But I'm not particularly knowledgeable about that so I wouldn't be able to say what complies. I think you may have an issue with your diagram with 917.5 on the upper shower drain vertical offset and possibly 917.7 and/or 917.8 on how the bottom WC joins. Again, not sure.

And on that vertical offset on the upstairs shower drain, that's something I missed and would need to be eliminated for any venting other than IPC 917. Generally the vent connection to a trap arm must be made within one pipe diameter of fall from the trap.

Cheers, Wayne

 

[readytowork]

Would IPC Section 917 allow for the design given that it is only 2 floors? I'm trying to understand what a design would look like using that code section for single stack vents.