Main vent stack size needed

[ineedagarage]

Hello all

I'm putting in a half bath plus a slop sink. So one toilet and two sinks. All within four feet or so together. I have the 3in waste pipe coming in so do I need to run the 3in all way up and outside or can I get away with 1 1/2 or 2 pipe? If I use the 3 I'm going to have to remove a stud and use a 45 angle to get it to clear. Thanks for the help.

 

[thooks]

2" is fine if you have another vent through the roof in the same structure.

 

[2Big2Ride]

2" is fine if you have another vent through the roof in the same structure.

We have a similar situation - what if I don't have any other vents since it is a new detached garage that will have a full bath, plus a second sink? My plumbing books are not clear on this subject. Can't decipher if the vent must stay 3" or it can be reduce to 2" pipe. I am assuming needs to stay 3" because it is the first and only vent in structure - and it isn't going to be fun to run up through the wall.

 

[brownbagg]

legally the pipe can be one size smaller than the drain pipe, so on a three inch pipe, 2 is legal

 

[motorcycle79]

It depends on your state or city code it is different every where. in Wi u have to have one 3 in stack vent Min

 

[kbs2244]

The code I have seen most often in freezing areas is 2” is OK to within 18” of the roof.
Then you have to go to either 3 or 4 inch to the outside.
The concern about small pipe outside is that frost from the humidity will freeze up and block the venting.
By going to a bigger pipe they reduce that chance.