Misaligned rough in drain pipe and HVAC vent

Question

I roughed in a VERY small bathroom in the basement, then had an HVAC crew replace some old vents with more discrete boxes to create more headroom. Every inch counts. Problem is, the washer drain on the floor (bottom of image) is now directly under the box vent branch going upstairs (top of the image).

I was going to frame the washer drain inside the shower wall, but now I'm not sure how to frame it under a vent. If I shift the wall 5" to the left, it makes the shower too small. 5" to the right makes the shower bigger, but it puts the washer drain inside the shower. My dad had the bright idea of shifting right and building a corner shower seat over the drain to hide it inside the seat/wall.

Is that doable? Or is there a way to build the wall underneath the vent? Thanks for your help!

Answer 1

If I understand correctly, the wall will be where the darker lumber is on the floor. If you extend that wall vertically, it will end up under the silver duct on the ceiling and you'll be left with no way to attach the wall to the ceiling so it'll wobble.

Based on that understanding, I'd build a small soffit on the ceiling to box in the duct and attach the soffit to the floor joists on either side of the duct. You'll now have lumber spanning across the duct and will be able to attach the new wall to that lumber, giving it the needed stability.

Of course, as you mentioned, headroom is at a premium, so you will want the soffit to be only deep enough to conceal the drain pipe when it gets to the ceiling. You'll need to provide enough room to hide the hub of the 90° bends necessary to make it turn horizontal (to avoid the duct), then back vertical to pass next to the duct. Depending on pipe size, you'll probably only need a 2x4" (4" dimension vertical) to hide the fittings in the ceiling.

The other option of building a seat into the corner of the shower to hide the pipe in the floor and the necessary bends to get it into the new wall (shifted to the right in this photo) is entirely reasonable as well, so long as you can stand to loose the floor space.

Answer 2

Install firring strips perpendicular to the joists and attach the top of your wall to the firring strips. Then run your vent horizontally through the wall and in to the existing wall. From there you can keep going sideways until you clear the duct, and then go up.