How far can a drain be from the stack before it requires its own vent?

Hi Hwill

That depends on the size of the drain pipe AND what state you live in... ;)

If you have an 1.5" drain pipe then 3-5 feet is maximum distance from the stack until you need to install another vent.

If you have a 2" drain then 5-6 feet is the maximum distance.

As noted, the exact distance requirements will be dependent on your state code requirements.

Mark

I want to move my sink to the opposite wall
Mark's correct about the distance between the trap and vent. That's great if you're going to simply mover it on down the wall. But you wish to move it across the room.
This is major surgery. First the drain will have to be moved and, if you're wet venting the tub. Connected back into the tub drain. But that's just the start. Next you will have to run a vent off the lavatory either out the roof or revented back to a dry vent. I haven't even addressed moving the water but that's got to be moved also. Still want to move your lavatory? If you do we can help.
Let us know, Tom