I need to move a toilet to the other side of room approx. 6 ft. I will have to drill a 3.5 in hole for the waste line in five floor joists on the second floor. Can I double them and still drill the 3.5 in hole and be in compliance?

  • You won't get a 3" pipe through 3-1/2" holes unless they're perfectly aligned and you have end access, but even if you do they're likely to creak and squeak. You need 4" holes. – isherwood Oct 2 '20 at 13:42
  • Far more important than the number of joists you're crossing is how deep the joists are. If you've got 2x6 joists, heck no! If you've got 2x10 joists, maybe, if you've got 2x12 joists, probably. Please edit to let us know how big they are, what the span is, and how close to the end of the joist the hole will be. With that info, someone should be able to give you a reasonable idea if your plan will work. – FreeMan Oct 2 '20 at 15:07
  • Does this answer your question? What are the guidelines for holes in joists? – Ack Oct 2 '20 at 15:51

enter image description hereThis bracket provides a building code approved solution for holes up to 6" through as many joists as you want - Joist Hole Reinforcer. Full disclosure, this is a product that I sell for the exact application in question. There are other ways to reinforce joists with holes, but I believe this is the only one that is code compliant out of the box. Hope this is is useful and helpful to others, not intending to spam.

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    Structural engineer here. I reviewed your site and did not see information to support your "building code approved solution" claim. What exactly do you mean? That it's not code disapproved? - Also, what problem / issue does this product does this address exactly? – Ack Oct 2 '20 at 16:04
  • Ack - We have a Code Compliance Research Report CCRR-0279, by Intertek addressing compliance with 2018, 2015, 2012 IBC and IRC evaluated for structural performance. What this specific report addresses reinforcing of 2x10 joist with holes up to 6" diameter. The report details specifics of code compliance. A copy of the installation instructions and the code compliance research report are included with each bracket. I will post a link to the report shortly. – Daniel Wensley Oct 2 '20 at 18:42
  • Link to Code Report and Instruction for further clarification - cdn.shopify.com/s/files/1/0275/0169/1018/files/… – Daniel Wensley Oct 2 '20 at 19:12
  • FYI, that report expires in only a few days, and the new one will replace it. :) I hope you all don't mind me posting about one of our products. Holes in Joists is a common issue and many people seem to appreciate finding a simple solution instead of having to spend sometimes thousands to replace joists. I hope it helps. – Daniel Wensley Oct 2 '20 at 19:24
  • Thanks, Daniel. Please add the relevant portions of that information to your answer. Comments are temporary. – isherwood Oct 4 '20 at 14:53

Not unless they are 2x12 floor joists and it goes exactly through the center. The maximum permissible boring in a floor joist is limited to 1/3 of the height of the joist (with a 2" minimum). See IBC 2308.8.2.

Sistering the joists would not effect this restriction, as it is an issue of the structural integrity of the framing member - not an issue of the required lumber dimension for a given span.

  • That's what I figured, I was hoping by doubling them it would work, I couldn't find a solution to this in the building code – Joe m Mar 23 '14 at 23:20
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    You run the pipe somewhere else (possibly straight down in a plumbing chase), you put in a pair of support beams below, you rethink moving the toilet, you sell the house and start from scratch elsewhere... – Ecnerwal Mar 24 '14 at 0:57

You need to box off that floor joist. You can remove an section of the joist in the way. You then build a box connecting the ends of the cut off joist to adjacent joists with perpendicular ties of the same dimensions of lumber. 2X10's for example. These ties transfer the load to the adjacent joists and give you an opening for plumbing or duct work.

  • How are you proposing a person box five joists? – isherwood Oct 2 '20 at 14:08

Bored Holes

Simply following building code, you'll only be allowed to bore a 3-5/64" hole through a 2x10 joist. A 2x10 is actually only 9-1/4" deep, and building codes set the maximum hole size to 1/3 the depth of the member (9-1/4" / 3 = 3.08333").

Adjusted Framing

If it was only a joist or two, boxing off the section might work. Using this approach for 5 joists, may or may not be the best way to go.

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Joists before

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Joists after

Engineered Plans

Another option, is to consult an Engineer. The Engineer will be able to provide a solution, and will include all the documentation required for the solution to pass inspection.

enter image description here
Engineer approved solution

NOTE: While the above image was a solution designed by an engineer, it is not a solution that will work in all situations. This solution will not pass inspection without the proper documentation.

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