Sister floor joist to improve headroom


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Old 04-02-23, 12:42 PM
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Sister floor joist to improve headroom

Without me having to pay for an engineer to answer this - In my basement (1910) I have 2x8s spanning 10ft for the first floor joists. I would like to put a total gym down there but need 3 more inches of head space. Is it possible to sister (2) 2x4s on either side of 1 of the joists and support them on both sill plates then cut away 4 inches of the 2x8 in a 4 ft section essentially giving me (3) 2x4x10s spanning 10 ft? I am sure there is a reason this isnt done in homes besides cost but I thought I would ask.
 
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Old 04-02-23, 12:49 PM
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Absolutely not.
 
beelzebob voted this post useful.
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Old 04-02-23, 01:26 PM
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If I wanted/needed to remove a 4 foot section of a floor joist, I would double up the two adjacent joists, remove the 4 foot section, then install double up 2x8s crosswise to the cut ends of the joist and running to the doubled-up adjacent joists. This would transfer the loads to the adjacent joists. I'd use the appropriate metal joist hangers at the ends of the cut joist and to attach the header to the adjacent doubled up joists.
This is how it's done for stairway openings and things like attic ladders and should do the job. But I am not a structural engineer. And if you have wimpy subfloor above, you may end up with a bouncy area above the cut joist. Running a 2x4 (or two) across between the two headers couldn't hurt.
 
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Old 04-02-23, 01:38 PM
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Is that method called something particular so I can research more on it? Thanks.
 
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Old 04-02-23, 05:58 PM
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Here's a vid that pretty much covers it:https://www.youtube.com/watch?v=73_vpD-lLyY

Also, the center of the joist is the area with the most stress on it. If you can move your gear toward one wall or the other it would reduce the impact of the modification to the framing. Not a huge deal, but if you placement isn't critical, moving it helps a little.
 
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Old 04-02-23, 06:48 PM
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This is a bad idea that needs to be stopped before it even begins. You don't cut or notch 2x8 floor joists 4" and 2x4s are not used as floor joists to span 10 feet.

Carbide Tipped's suggestion in post 3 would likely work. But you would not rip, notch or sister your joists with 2x4s.

See: https://up.codes/s/irc-502-8-cutting...g-and-notching

So this thread is closed.
 
 

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