Direct vent bathroom and kitchen sink into main stack?

[rdubbs]

Currently, the bathroom and kitchen sink drain directly into my houses main 4" stack individually. The connection for the bathroom sink is broken at the stack so I am going to replace the whole stack and drains with pvc. I want to tie the lav sink and kitchen sink into the same drain using a wye connection. This is a single floor house with basement. There are no other connections into the main stack above these.

My question is, since they are both very close to the main stack (within 3.5-4 feet) can I just direct vent both into the main stack without having to build a new vent up and around back to the main stack? Take a look at the illustration of how I want to set it up. Thanks!

 

[Terry]

Is this 4" a vent for below?
Is this a vent for a toilet on the main floor?

If you intend to rerun the pipe in plastic, using the 4" as a vent, you would use santees at the 4" vent, no combos or wyes.
The trap arms would grade at 1/4" per foot, with a max of 42" on 1.5"
Longer than that, and you should revent back to keep the distance within the proper limit.
A lav can install over the kitchen sink, but not the other way around.
If you use fittings to turn the pipes up, you lose your venting. In that case you will be adding vents and tying them back to the stack.

 

[Sponsor]

 

[rdubbs]

Thank you very much for the info. I plan on using a 4"x2" sanitary tee at the main stack. The 4" stack is the main stack for the house and does have two toilets from main level that vent into it below what is pictured.

I am not sure what you mean by using fittings to turn the pipes up... do you mean that I should not have a vertical drop from either of the connections from the p traps to the drain? So pretty much staying horizontal with a 1/4" grade per foot from the connection for the p trap all the way to the 4" main stack - which is pretty much how it is now? Height wise, the bathroom sink connection would be slightly higher than the kitchen sink connection, this is ok, but not the other way around? Something more like what is pictured below?

 

[Terry]

If you jog a pipe above the 1/4" grade, it no longer vents itself.

 

[rdubbs]

Thanks again for the reply. Not exactly sure what you mean by joggin the pipe... I am guessing you are saying that there can be no curves above the grade? Would I need to run separate 2" pipe for each sink to the 4" main stack - which is exactly how it is now - then have two sanitary tees on top of each other on the main stack? The top would have to be the lav sink and the bottom the kitchen sink? Similar to picture drawn below?

 

[Reach4]

If you plan to cut that cast iron, make sure you secure the part above the cut before cutting.

 

[Jadnashua]

The trap arm to the drain must have enough room in it to allow both the waste water to flow while also allowing air to move above it. If you exceed 1/4"/foot, the max distances to the drain no longer apply, and you have to have a separate vent (or revent) for that fixture. For example, a 2" pipe, your trap can be no more than 5' from the drain. 5' at 1/4"/foot, 1.25" (leaving only 3/4" space if you drew a level line from one end to the other), which should provide enough air space above so that the trap doesn't siphon. Smaller pipe, shorter distance, longer pipe, longer distance.