Can I cut a notch out of 3 floor joist?


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Old 07-28-22, 10:27 AM
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Can I cut a notch out of 3 floor joist?

Need to run a shower drain and my center hole ended up right along side my floor joist. I'm going to have to cut out a notch about 3 inches on top of my 2x12 joist. I'm also going to have to notch out 2 other joist to the right in order to connect my piping to my sink drain. Will this cause any problems taking a 3 inch notch out of the top of my joist?



 
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Old 07-28-22, 10:31 AM
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If you search online there are many sites that go into full detail of what you can and cannot do. It looks like your notch will be near the end of the joist which is permitted but can be no deeper than 1 7/8".

 
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Old 07-29-22, 04:04 AM
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I've been reading online that putting a notch in a floor joist is worse than drilling a hole through it. I'm right along side of my joist but that's the center of the hole I have to drill for 2" pipe, still need to go a good inch or so into the joist. I may just be better off to cut a piece of the joist out and make a box opening, even with a box opening I'd still have to drill a 2 1/2" hole through the cross brace for my piping but I believe I'd be safe seeing it's a 2x12 and I'll be within the 1/3 of the span..



 
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Old 07-29-22, 05:19 AM
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I've been reading online that putting a notch in a floor joist is worse than drilling a hole through it
In case anybody is interested, the reason for that is the bending moment of a beam.

A hole placed in the middle of a beam be it wood or metal puts no stress on the member to hold a load. The outside or edges of a structural member is where all the stress and load is being brought to bear and therefore needs as much material before no bending takes place as indicated in the attached sketch.


If material is removed from the top or bottom edge then you are effectively reducing the ability (or size if you will) of the member to support a load as the second picture shows.


This can easily be demonstrated by taking clay or any flexible material in the shape of a wood beam. Put a hole near the top edge and then bend it and watch as the top surface breaks apart. Then put the hole in the middle and do the same. It take longer and more force to break the fibers on the outer edges than before.


Removing material from the middle of a beam does not affect the outside strength or bending moment of material. Most steel and aluminum member will purposely have holes in the middle of the beam to reduce weight without compromising strength.

 
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Old 07-29-22, 05:23 AM
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Eh, if it's a shower, I've seen floor pan drains that are dead center, AND some that are offset to the back.
And (Realtor 24+ years) I've seen a few homes where the owners turned the floor pan 90 right or left to avoid cutting through a floor joist.

HOWEVER, have also seen where a homeowner ran a saw-z-all along the top and sides of the joist to cut the nails, pounded the beam over 2" with a sledgehammer, then used screw-in joist hangers to re-connect everything.

I'd consider sistering the beam- and you don't necessarily need to have the sister-beam the same size as the beam, don't know if there is a code specification, but rule of thumb is 2x the size of the hole you are cutting. (round hole is much better than square notch)
 
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Old 07-29-22, 05:48 AM
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Originally Posted by Norm201
​​ ​​​​​Removing material from the middle of a beam does not affect the outside strength or bending moment of material. Most steel and aluminum member will purposely have holes in the middle of the beam to reduce weight without compromising strength.
A common example is the I-beam or box-beam, where all the material is at the exterior.

The neat example is probably early WWI wooden biplanes and triplanes, which IIRC, would have wooden spars and crossmembers 'lightened' by running and deepening a circular profile router along the wood to remove as much wood from the center which was NOT under stress* from compression or tension, leaving most of the wood at the edges where the stresses produced movement / strain.

*Stress is the force applied. Strain is the deflection/deformation of the material in reaction to the force.
Sounds more 'science-y" than just saying 'squishy-ness'.
 
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Old 07-29-22, 10:50 AM
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Don't think I can notch the joist anyways, I need to have a 2" tee or elbow right below the stand pipe of the drain. I would have to notch the top of the joist at least 2 1/2 inches which would put me way over the depth allowed. Guess the only way to do it is to cut a piece out of the joist and make a open box frame. It was the last drain I had to run, couldn't get lucky enough to have that joist just a few more inches over to the left....



 
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Old 07-30-22, 04:24 AM
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Originally Posted by mark249
Guess the only way to do it is to cut a piece out of the joist and make a open box frame.
I don't see any nails or screws connecting the beam to the flakeboard-

In that situation, I'd disconnect the beam from the plate and sledgehammer the beam an inch or two over to the left to get the clearance. Minimal effect on floor load, major simplification to the project.
 
 

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