Slab On Grade DWV Design Questions

[jb9]

Hello,

I was wondering if anyone has any thoughts on the best practices for running DWV under a slab on grade. I am building a small accessory unit with a "wet room." The unit is going to be 12'x16' and I am designing a very small wet wall between the kitchen and bathroom. The shower will essentially be a concrete sloped floor with a drain in the bottom.

Here is a question I have:

-I am trying to keep my pipe runs UNDER THE SLAB to a limited length. I know where I am going to tie in to a main line once outside the structure foundation. Is this a best practice? Or is it ok to run as much piping under the foundation as needed. I am in a cold climate so I am curious as to what the pro's consider to be a well-designed DWV under a slab on grade.

Here are some pictures. Am I missing any vents? Does anyone have any better suggestions on how to run the DWV? Again, I don't have much space and I want to keep pipes off the exterior wall. In the picture, I haven't drawn the slab so just imagine I will be deep below the frost line too.

Thanks.

 

[jb9]

I think I am missing a vent so I drew a Combo Wye with a Side Inlet (3x3x3x2). Is this better? I am assuming that flat fitting has to be a Wye. I just don't know if that 2" side inlet can accept waste (sink).

 

[frodo]

.............

 

[jb9]

Thanks Frodo. I'm not that great at reading DWV Isometrics... Can you annotate this bottom view of my model with the most intuitive way you would route just the drain pipes under the slab? What does the 3" tee with 2" side outlet look like? I have a good feel for the venting part (and the fittings), but I don't have a good feel for the horizontal. I can use your DWV to see where the fittings you suggested will go. Sorry for being so ignorant. Your knowledge is impressive!

 

[frodo]

if the distance from the SO tee to the 2'' trap is more than 6'
swap position of the tee from under the lav to under the kitchen sink, so it is within 6'

 

[frodo]

if the distance from the kitchen sink to the drain is still over 6'
you can move the drain for the sink closer to the shower and use a trap arm to drain the sink
as long as trap arm is not longer than 3'

so your 2 critical distance measurements are 6' and 3'
do you understand?

 

[jb9]

Ok. I think I got it now... I think one of the strengths of your idea is that it reduces the amount of sewer main under the slab by bringing the shower and the toilet together. I added a dimension of the depth that will be required to bring my main to the street from the rear of my building site. This accessory unit will be towards the back of the lot and my frost line is 32" deep. What do you think?

PS. The shower drain is about 3' 6" from the lav stack.

 

[frodo]

it will work

 

[jb9]

Thanks Frodo. I appreciate it. I will use a 90 degree 1/4 Long Sweep for the fitting at #6. I will draw it in as well as the two way clean out you indicated. What is the difference between using two wyes as directional cleanouts vs. using the single multi-directional cleanout Tee that I see?

 

[jb9]

Like this one...

 

[frodo]

one is just as good as the other, I prefer using 2 combos like you have in your drawing