I have a PVC vent stack that arises from the concrete floor of a one-level home, and rises straight up through the ceiling, into the attic, and out the roof. The stack is currently in a wall.

I want to enlarge the bathroom by moving this wall back about 1-1/4 feet (into the closet). To do this, the stack must be cut and angled back with an elbow, then routed upward parallel to original stack location, and then reconnected with the original stack in the attic.

A contractor says his plumber can angle the stack back by cutting the stack about 6 inches above the floor and installing a long 90-degree elbow, then a small (4 inches) length of PVC angled slightly toward the ground, and then another elbow (45 degrees) connecting to a three-way sanitary tree. The sanitary tree would connect to the new vertical vent stack. The new vertical stack will re-connect with the original stack in the attic.

The small (4 inch) piece of PVC will not be horizontal, but close (maybe 88 degrees), tilted toward the original vent pipe.

The sink waters (two sinks) will drain into the sanity tree arms, which will be connected via PVC pipes pitched slightly downward for drainage.

Will this configuration be safe for venting sewer gas and allowing water to drain downward, then into the curved elbows, and into the original stack, which is coming from the concrete?

Thank you.

Vent Stack Angle Backward (based on previous work)

  • Why do you think the plumber would suggest this if it is not "safe"? Why don't you value the advice of your "plumber" Or is this a 'plumber" you found in the bar?
    – Solar Mike
    Commented Mar 16 at 7:56
  • The soldering skillz do not impress...
    – Ecnerwal
    Commented Mar 16 at 13:01
  • 1
    A picture is worth a thousand words. Why not just ask if the plumbing in the pic is acceptable. It is.
    – RMDman
    Commented Mar 16 at 14:57

2 Answers 2


I do not know where you live, but this arrangement would pass any plumbing code I know.

The section from the bottom outlet of the tee down to the floor receives drainage from the sinks, so it must meet drainage code requirements. When changing drainage direction from vertical to horizontal, you must use two 45° elbows (or, in many US locations, a long sweep 90° elbow). When changing drainage direction from horizontal to vertical, you can use a 90° elbow. This matches what has been done in the provided photo.

Once 6" above the flood-level rim of the sinks, the pipe would be considered a vent and can change direction with 90° elbows.


The bottom section is a wet vent, a drain. This is not subject to the "6 inch above the highest faucet" rule. If the vent is reconnected at 90 degrees and is way up in the attic, this is fine.

If you have a clog below the PVC coming from the floor, the water obviously will fill this area before filling a sink(s) above.

As far as sewer gas, this set up is fine. The gases will rise up and out as if the stack were vertical the entire path.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.