Need fast opinion on 4" hole in joist!

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Old 12-05-11, 07:03 PM
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Need fast opinion on 4" hole in joist!

My basement is coming along very well now because we have a small crew working daily on it, seem pretty competent and I like their work.

My question is this--and we are dry walling tomorrow so I need to know fast--for the bathroom exhaust we can either run 20' down a joist bay and cut the 4" hole in the rim joist only OR we can cut the hole through a joist that is next to the rim joist at the other corner of the house and then the rim next to it. This is a much shorter run and slightly easier install but I am hesitant about that big a hole in a spanning joist, even if it is pretty close to the edge of the house.
 
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Old 12-05-11, 07:50 PM
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No to cutting through the joist, yes to cutting through the rim joist.
 
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Old 12-06-11, 02:17 AM
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Yeah I really hate to do it even though it's in a great spot to do it (if one had to) from a structural perspective. Cutting the middle third out of the joist is ok, but a 2X10 joist that gives about 3" since they are barely over 9" high, so this would be over that (and 4" to 3" reducer on duct work gives a fairly serious reduction in airflow). However, if I get it sistered first it should be ok, so I'm going to ask him to do that, that way he gets his short run he wants and cut through the joist and I get my joist strength
 
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Old 12-06-11, 04:17 AM
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Brant, I wonder why the question was asked if the OP was going to cut the joist anyway?
Skoorb, since you are going to cut it anyway, you will need to support the joist on either side of your cut with 2x10 perlins to each of the adjacent joists, in addition to sistering it. He is using solid metal duct, and not the plastic or corrugated cheap stuff, right?
 
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Old 12-06-11, 09:15 AM
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I wasn't going to cut it anyway I was leaning away from cutting through it, but then I saw some pretty big holes in joists (online) made structurally sound with sistering the joist beforehand, so I figured this would let us cut through it.

It is going to be solid metal duct.
 
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Old 12-12-11, 03:50 PM
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Ummm... if you cut a hole in both joists, it's still a 4" hole and still likely not enough structure to keep things from sagging..... It probably needs more support than that to carry the load it is handling. You really ought to be consulting a structural engineer to see if you need a support pole or something to help with that load.
 
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