My laundry wall lands DIRECTLY on top of an I joist in my basement. They are parallel so moving one side or another will not allow me to miss the I Joist. There is no method to vent up because a truss lands directly on top of this wall. This means I need to go down, and have to drill a 4" round hole through my I Joist top flange and probably 1/3 of the I-Joist web.

I know this basically ruins the joist. BUT I will not be touching the bottom flange. In addition, I have a wall that is partially below this I Joist, meaning in the basement I have probably 2" of flange bearing on this wall which is parallel with the joist.

Right now all I can think of is: Attach a 4' long 2x4 or 2x6 on the side of the top plate & studs of my basement wall to ensure 100% of the joist bottom flange is making contact with the wall for about 2' on each side of what would be the weakened area. I would also ensure there is contact to this wall at all points with shims if needed (Basement wall is not there as load bearing, so it may be 1/8" shy of making contact with the I Joist flange right now).

I would create an X brace for the top flange to bear load on both joists next to it but I have plumbing on both sides! This also means I can't just run another I Joist or 2x12 near the weakened joist. I am not sure how much load bears on each flange but I would assume 45% of weight is on the top and 45% on the bottom with 10% or less in the webbing.

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    Why not put the hole in the floor next to the wall? – JPhi1618 Oct 25 '17 at 13:57
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    My thought exactly. You could even build a half-wall and finish it with a top cap to act as a shelf. Cutting the joist should be a last resort, and you'll be hard-pressed to get anyone here to sign off on a cobble fix. Is the basement wall fully supported with a footing? – isherwood Oct 25 '17 at 13:58
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    And your reasoning about load percentages reflects a misunderstanding of the joist as a system. The top flange is in compression, the bottom in tension, and the web some of each depending on the momentary forces on it. It's not as simple as proportioning things out. By cutting the top flange you create substantial squeeze on the new gap. By cutting the web you reduce the stiffness of the system markedly. – isherwood Oct 25 '17 at 14:10
  • If I cut the hole in the floor 2 things - the dryer now sticks out 4-5" making it stick out past the bathtub and 2, I can't get the vent in the joist space because there is plumbing. I'm aware it's not proportional, I just wanted to iterate that I know the flanges are the bread and butter of the system. saying each one does nearly all the work while webbing does little. I am looking hard for another option besides the entire flange being destroyed. I'd feel more comfortable with only half of it missing. So far I have found some oval adapters...? This is such a snafu but has to be done! – Nic Oct 25 '17 at 14:17
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    Can you vent it out through a side wall instead of down through the floor? Maybe up inside the wall until you're above the dryer, then come out of the wall and go horizontally to an exterior wall? – Mark Oct 25 '17 at 15:25

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