Doing a bath remodel and upon tearing out the drop in tub, I came across a notched TJI joist. (and then some at 4 1/2") There is another joist 5" away so it makes me wonder if the notch is OK?

To make matters worse, my new stand alone tub drain needs to sit smack in the middle of the two close joists. A 5" hole (white circle in picture) is needed to accommodate the jacuzzi mz20000 adapter.

Can I go ahead and notch the already notched joist for the new drain, or do I need to cease and desist with joist notching?

Any ideas here are very much welcomed, I am stuck.

The setup: Setup

The notch (4 1/2") Notch

Logo - No series number found Logo

Closeup of master blueprint Closeup of master blueprint

2nd floor blueprint 2nd floor blueprint

First floor blueprints enter image description here

  • 1
    Based on a quick look at mine (same logo, TJI silent floor) the series number should be on the side of the bottom, but is only printed every 10 or 12 feet, so it might take a camera on a selfie stick to find one from that size hole. – Ecnerwal Apr 8 at 1:30
  • How long is the span of the joist - i.e. how far is this from the nearest support? Figuring out what sort of load it has on it will be important. – Luke Briggs Apr 8 at 3:46
  • Also the close together joists might exist for the purpose of supporting the tub anyway - you'd need to inspect more under the floor to find out why it's like that though to be sure. – Luke Briggs Apr 8 at 3:49
  • Consider whether you can raise the tub slightly and build an offset in before you drop it in. Notched joists are bad. – K H Apr 8 at 4:04
  • I looked at the joists in the basement and found the series to be 15 DF. I found the design specs here techsupport.weyerhaeuser.com/hc/en-us/article_attachments/… – Cory S. Apr 9 at 17:14

Don't notch the flange of an I-joist

But don't panic! There's likely good news below too.

The flanges - that's the top and bottom pieces of an I-joist - take a significant proportion of the actual load. Cutting them makes a quite dramatic difference in the load bearing capability of the joist, according to manufacturer load tables like the ones below.

enter image description here

I-joist manufacturers provide documents on how to safely cut into an I-joist, and this manufacturer document directly states that they should never be intentionally cut:

The flange of a TJI®joist should never be deliberately cut or notched and TJI®joists subject to damage prior to installation should be discarded and replaced.

The document goes on to suggest suitable ways to repair a side notched joist (this isn't one of those unfortunately!) by essentially nailing a board to the side of the joist, or "heading off" the I-joist by nailing a new flange to the side:

enter image description here

The doubled up joist is a good sign though!

Builders will double up a joist when extra load is expected and that's typical in bathrooms around a very heavy tub full of water. There's a good chance that the additional joist exists for the purpose of supporting the tub, meaning one of them being a bit damaged to accomodate the tub in the first place isn't a major issue, but you should absolutely check where those joists go or have a surveyor take a look to be sure. An easy way to find out quickly is to check the joists around the other end of the tub if they're also doubled up.

Aim to get the weight of your tub spread evenly across the doubled joists. If the jacuzzi is notably larger than your original one, additional joists might be needed to support the load, and avoid cutting the flange as much as possible. Raising the tub up a little bit such that you can add pipework that bends around the joists may be your best option there if you're limited on moving the tub around.

  • Thank you Luke for the detailed response. I have seen the manufacturer literature, but found it a bit confusing. You response helped clear some of that up. Unfortunately we have very little wiggle room for an alternate location. I have considered building a platform for the tub as you suggested, but that will be a tough sell for my wife who wants "seamless" floors. – Cory S. Apr 8 at 13:48
  • @CoryS. any scope for flipping the tub around so the drain is at the other end and maybe then happens to land on a space anyway? – Luke Briggs Apr 8 at 15:19
  • I had considered that, but since it's a soaker tub, one end is taller than the other and would look silly flipped the other way in the space I have. Thanks for the suggestion. – Cory S. Apr 9 at 17:09

If you only replace the old tub with the same, I would have told you not to worry too much if you can bridge the notched wood with the same kind (the cord is under compression, as opposed to tension, which can be a serious matter). But I don't think your floor was designed for the Jacuzzi. You should obtain a nod from a structural engineer before proceeding with anything.


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