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How big a hole can I cut into a floor joist and be okay?

How big a hole can I cut into a floor joist and be okay?

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Old 11-13-20, 04:35 PM
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How big a hole can I cut into a floor joist and be okay?

Good afternoon

Hopefully someone has some insight for me. I'm renovating my kitchen and found about the worst hood fan ducting job someone could do. They used plastic vinyl flexible pipe., went horizontal across a wall cutting completely through a load bearing walls 2x4 and did not double up on either side.Its also got effectively 8 X 90 degree bends in it. It looks to me like they meant to install the stove 4 feet to the left of where it ended up and that's how they made it work.

My plan is to tear all that vinyl crap out. Replace the 2x4 they cut right through and run new solid metal 4 inch duct out with only 2x 90's. My issue is that I'll need to cut a second 4 inch pipe hole through a 2X12 floor joist (16 inch centers) . The original 4 inch hole is 3 feet to the left of where the new one will be. Is that okay to do code and safety wise? Its just the one joist I have to go through. I was thinking I'd piece in the old hole with screwed and glued 2X12 on either side if need be to shore it up.

Thanks!

Edit: In case you are wondering its a 3 story house kitchen in the middle so no easy attic route.
 
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Old 11-13-20, 06:57 PM
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The second worst thing was using 4" duct unless you mean 4"x10".

The hole cannot be larger than one-third the depth of the joist,
so the maximum hole size for a 212 joist (actual size 1-1/2 x 11-1/4 in.) is 3-3/4 in. diameter.
 
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Old 11-13-20, 07:01 PM
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Old 11-18-20, 08:48 AM
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I've pulled some drywall out on the other side of the wall and it dawned on me this span is not just a free span. Its nailed cross ways to the floor in the kitchen every 16 inches. I've attached a rough drawing from a top view. This must change how big a hole I can cut but by how much? In an ideal world I would like to go with a bigger pipe like 6 inch.....

Red line is the hood vent path outside.

 
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