Hi I am in the process of installing a range hood in my basement and I need to snake the 6” vent through a I-joist to get it to a place where I can drill it out through the rim joist. The question I have is that all of my I-joists run left to right (see picture) but for some reason there is a small area where it’s running the other direction only for a short span. I don’t believe it’s load bearing but for some reason the builder doubled up on the ijoist in that spot so I’m worried it’s structural. Any advice greatly appreciated! enter image description here

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    How deep (tall) are the I-Joists?
    – Ecnerwal
    Dec 5 '21 at 5:30
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    If the joist wasn't bearing any load they wouldn't have put it there. Dec 5 '21 at 6:05
  • I believe the i-joists are 16" tall. Its a strange setup I haven't seen in other parts of the house. I am not sure why they didn't just put another long span and put those short sections. Could it be that the width was too close to put another long span so they decided to put short diagonal sections with hangers to bridge the next span to the foundation wall? I'm kind of stuck at the moment with my install because I am not sure what I need to do here. Dec 5 '21 at 6:39
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    The most common reason for a framer to box out joists in that manner is to make space for a plumber’s pipes— very often a toilet in the room above. And yes it’s structural in the sense that joists are always structural. They hold up the floor above!! Dec 5 '21 at 6:56
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    The doubled up i-joist is carrying 1/2 the load of the two i-joists that are hangered into it. The area to the left of the double is the area that was framed out - maybe the builder boxed it out for the 6" hood fan duct you are trying to run. Who makes your i-joists and have you verified you can drill a 6" hole in the i-joist based on their joist hole chart? Here is an example - mavbldgsys.com/joist-hole-chart.pdf Dec 5 '21 at 7:23

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