Drain vs Joist! Help needed!

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Ed Rogers

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We see this is a common issue on quite a few posts however ours is unique: Our new install of a prefab shower pan has the drain coming dead center of a joist. Today we spent 8 hours (literally) searching for answers. We found boxing and sistering and understand them all however if you take a look at our images you will see just how unusual this problem is. Boxing is out of the question is seems so where to go from here is a mystery.

Unfortunately, we invested in the pan, glass doors and everything else needed to complete the job. We expected some creative challenges regarding the water lines but not the drain. We're extremely competent with plumbing and electrical and have done our fair share of "complicated" projects but this one seems to have stopped us dead in our tracks like a brick wall. Our absolutely last resort would be to do a custom "mud" tile pan which we really want to avoid. We have two professional plumbers coming in tomorrow for advice.

Attached are two images which will tell you all you need to know. All practical suggestions are welcome.


The Plumbing Wizard
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Bothell, Washington
Wow! What you have there is all wrong.
That should have been a wye off the main line, not a santee.
You can't raise the trap arm with a fitting. It stays at a 2% grade or 1/4" per foot.
You can't use a vent 90 on the drain, it should have been a 45 or long turn 90 and at the least a medium 90. There is no justification for the "vent" 90 which is used above the flood level on a vent. Typically 42" above the floor.

How far back can you go on the floor joists? You may be able to offset some, like about 3" if you don't want to box it out.
Of course going with a custom pan also fixes it.
Hey, wait a minute.

This is awkward, but...

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