Roughing in need help

Hi everyone, I am new to the forum.

I am building 2 detached office buildings in my back yard, both of these structures will be on concrete slabs.

I will be putting bathrooms in each of these buildings and need to know a couple of things so I can get started before we build the foundations.

What size (PVC) pipe should I use for each toilet drain?
In other words where I stub up through the concrete slab, what size should the pipe be for the toilet flange to connect to?

Secondly, I will be digging an access underneath my existing house to connect each of these drains to the existing drain network of the main house, so my question here is where exactly should I look at making these connections?

For a little more detail, lets call these buildings the "east building" and the "west building"

The west building is really close to the master bedroom/bathroom.
The east building is closer to the kitchen drain than another bathroom drain.

In a perfect world, I would like to connect the east building bathroom drain to the kitchen drain of the house and the west building bathroom drain to the master bedroom/bathroom drain.

Please let me know if this is doable and where in the existing drain network I should plan on making the new connections.

Thanks a lot everyone.

Scream

Toilet drains need to be a minimum of 3". The size of the drain lines is dependent on the quantity of fixtures hooked up to them. A shower requires a 2" drain. Some places I'm told require underground drains to be at least 2", but a sink normally doesn't need one that big. You can always go from smaller to bigger as you drain, but never the other way. The drains need slope - nominally, they require 1/4" per foot, so that may be the biggest problem for you depending on the releative elevations of the various buildings.

You might have more problems than you realize...
You can only drain 3 WCs on a 3" main...
Chances are your line exiting the house is 3" and if you have more than one existing WC in the house, you will be over your limit...
A better solution may be to trench around to the front and tie in by the sewer increasing the line to 4" fromt he tie-in on out to the tap...
I would consult a pro on this one - sounds like you are in over your head...

A second thing I thoguht of...
Chances are you will not find a 3" pipe under the kitchen to tie into...
A sink with dishwasher only requires a 2" line...
Even if you have 2 sinks and your laundry room in that area, you still won't have the required sizing...
I cannot percieve any way other than trenching to the front of the house for you to do this...
Assuming you are going to have a permit for this job, the inspections dept will probably want to see a 4" tie-in per code anyway...
As well, the trench to the back can be used to carry the potable water if you choose...
Here the only stipulation is that the waste piping in the trench with the water be "DWV", not sewer grade and that it be tested with a 10' head as if it were in the footprint of the structure... (otherwise you have to bench the trench etc...)

Hey thanks for the replies Mark and JA,
Actually I did a major remodel to the house 2 years ago and replaced ALL of the drains at the same time we did a complete copper re-pipe, we tied into the main sewer line which comes up from the street using 4" ABS, the drain at the kitchen is 3" and includes the sink and dishwasher.

The 4" tie in to the sewer line happens right in front of my kitchen and travels beneath my driveway to the street main.

ALL of the drains under the house are 3" if memory serves me, we never stepped down to 2" anywhere under the house and in fact I think the only 2" we used were for vent lines up through the roof. I will have to look to be sure but I think thats what we ended up going with, it may be that the drain and trap for the kitchen sink are in fact 2" but it immediately hits a 3" right under the house.

I guess the bigger question is in order to comply with the 1/4" per foot slope, am I allowed to run pipe through the concrete footing of each building, if not then I have a big problem, as the grade for the offices and the main house are the same.

What are my options here with routing the drains out through the footing?

Thanks again guys for the replies.

In most cases, waste lines can go through foundations walls.

I've core drilled them, and I've used sledge hammers to knock the holes through.
On a new home, it would take a few minutes to knock a hole large enough for the 3" line.

Terry said:

In most cases, waste lines can go through foundations walls.

I've core drilled them, and I've used sledge hammers to knock the holes through.
On a new home, it would take a few minutes to knock a hole large enough for the 3" line.

Click to expand...

Hi Terry,
Thanks for the reply.
I had read somewhere that some areas do NOT allow waste lines to be run through the footing portion of the foundation, and that was the thing I am most interested in.
It would be much easier to run the line prior to pouring the foundation/footings than breaking the concrete up after the fact.
Any tips there?
Thanks!

For the section through the footing, sleeve it..
Get some 4" PVC and slide it over the 3" pipe going through the footing...
Protects the pipe from damage due to shifting/settling of the footing...

Awesome, thanks for that, that is exactly what I will do and it makes perfect sense.
Thank you!