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Unread 12-01-2019, 12:03 PM   #16
Madumi
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OK, sorry... toward the one side (away from the supporting wall), there is 43" unsupported, and toward the other side, there is 19" unsupported (for a total of 62" measured across the width of the bathroom).

Just let me know if I'm still being ambiguous :-)
thx!
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Unread 12-01-2019, 12:08 PM   #17
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The span across the room to be tiled has no bearing at all, Bert. You need to know the unsupported span of the joists.

I'll ask again about your drawing. On the bottom you show a center support vertically in the drawing with joists extending horizontally in each direction. Is that the same under the bathroom area?

Under the bathroom you have joists extending each way from a central support? And those joists have the same unsupported span as in the lower portion of your drawing?
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Unread 12-01-2019, 12:44 PM   #18
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Yes, I think that's right. The drawing on the right is only the bathroom.

I'll attach a drawing with a few more lines on it.

so sorry for the confusion...
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Unread 12-01-2019, 02:36 PM   #19
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That's very helpful. I though your first drawing was a plan view rather than an elevation section. Hence the confusion.

You've got a problem.

It's actually worse than just having overspanned joists. Depending upon just how the joists are treated where they overlap under your proposed tile floor, you could have a significant uplift in the center of your bathroom when a load is placed over that 13.5-foot joist span. The height of the movement may not be great, but it would be powerful and vertical movement is anathema to ceramic tile installations.

If the joist overlap is long and the joists well fastened together, that uplift would be reduced, but if the builder elected to use 2x8 floor joist material with wide spacing over that span, I doubt much attention was paid to the joist overlap, but that's just a guess.

My opinion; worthp price charged.
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Unread 12-01-2019, 03:20 PM   #20
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Hmmm, is there anything I can do? I am willing to set up joint sistering... Presently I don't think the joist overlap has been secured at all together.

Would you suggest any method to make the floor tileable?

Here's a pic (if that helps). I colored the top of the supporting wall red. Sorry for not moving the 2x8--it was placed there just to make walking easier.
Oh, and yes, the joist coming from the left, ends at the supporting wall. The joist coming from the right is the one that overlaps, probably 24" or so.

thx!
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Unread 12-01-2019, 03:25 PM   #21
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Bert,

I’ve run into similarly overspanned 2x8 and it was a bear to correct and required removing a bunch of drywall from the ceiling below. Do you have access from below and are you will to remove wiring and plumbing to sister in new joists?

Edit: just saw the latest picture. What’s the material under the joists?
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Unread 12-01-2019, 03:35 PM   #22
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Bert, you can tile over anything you feel comfortable with. We can only tell you what the industry standards are and what potential problems we see.

Some of the notching we see (not necessarily the ones over the support wall) are not good for your plan, either. Specifically one I see near the top left of the photo.
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Unread 12-01-2019, 04:02 PM   #23
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thx again for replies--much appreciated.

I am quite willing to do extra work to strengthen the floor. I'm just wondering what specifically I would need to do--at least to ball-park the appropriate stiffness required for tile.

eg. Bolt the overlapped joists+place a new 2x8 over the notched plank & then sister the joists on account of the 19-21" spacing?

The material below the Joists is 3/4" shiplap, yellow pine (I think).
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Last edited by Madumi; 12-01-2019 at 04:29 PM.
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Unread 12-01-2019, 05:45 PM   #24
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Living space below? Can you remove the boards to access the area? You will need to sister the joist over 2/3 - 3/4 of the span to be effective.

The link to my thread is below. I documented all of the painful details of the effort.
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Unread 12-01-2019, 06:53 PM   #25
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Here is what I would do.

I would add joist hangers and a header on the right hand side of the picture. Then I would add a full length sister from the outside wall to the new header. I think you only need to worry about the left hand side of the as long as you have a continuous joist.

If you want to go with a more risky option. For your tile to be safe only the floor under it has to meet the defection requirements. For this to work you would triple up the joists and add headers at both ends. You have some things good on your side, being over the load bearing wall, and the bathroom is small.

When sistering you want to use either nails, lag bolts, or structural screws. You want to ensure that you have enough support for shear load. Do not use drywall or deck screws.
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Unread 12-01-2019, 07:03 PM   #26
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A joist acts sort of like an I-beam...the top and bottom are the biggest components of the strength for stretching and compression...the middle holds them in place. Yes the more in the middle, the stronger it is, but it's the continuous top and bottom that make a huge contribution. That is the reason why codes do NOT allow notching the top or bottom of the joists, and where in relation to the ends it can have through holes. THey broke all sorts of those rules when they built your bathroom. When you notch a joist, it acts more like one that is the depth of the notched area, not the depth of the rest of the thing.

If tiling is really that important to you, you might want to contact a structural engineer.

The planks on the top and bottom of the joists helps make it more like a box beam IF they are really well attached.
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Unread 12-02-2019, 09:29 AM   #27
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Thanks again for replies

Yes, it's living space below, but removing the shiplap to sister 2/3-3/4 of the joist span is a little out of my reach presently.

I know it's also risky, but tripling the joists under the bathroom area is definitely attainable. If I went with that idea, just to check that I'm on the same page, one would bolt the joists to either side of the present joist along the length under the bathroom (i.e. it's intended to strengthen that span, not float when the original joists flex, right?)
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Unread 12-02-2019, 02:02 PM   #28
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Installing short sections underneath the floor over the beam won't help all that much. The real solution was mentioned earlier...sistering the middle 2/3rds of the joist runs. Think of those joist ends like a pair of scissors where the joint is at the beam. Any movement outwards in the span will cause the scissors to open. Trying to prevent that only at the middle is nearly impossible. You might be able to help if that was steel plate, but that's something a structural engineer would be more likely to be able to help with. Just bolting the bare joists would likely end up with them splitting.
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Unread 12-02-2019, 08:08 PM   #29
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thx again for replies.

Hmmm, I feel a little daunted by the prospect of putting in new joist spans, but oh well... There was some mold that occurred in the 1st floor ceiling from a leaking tub, so it might be just as well to check out the damage & attempt some sort of sistering.

my wife isn't going to like me...
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Last edited by Madumi; 12-02-2019 at 08:38 PM.
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Unread 01-03-2020, 05:19 PM   #30
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So... This is me a month later, saying "Thanks" for the guidance and suggestions. Three of the four supporting joists had cracks, so I ended up sistering in joists both directions, trimming them below level, so movement wouldn't impact the middle & placing 2x8's on the outside to support the floor. Oh, and cross joists, yes, well, the whole structure has a nice silent response when stomping on it now... :-)

I've attached the before & after.
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