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Unread 06-08-2021, 09:07 PM   #1
Chibo22
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Looking for deflection advice, new kitchen reno

Hi there!

I recently purchased a 1950's house and I'm beginning my kitchen reno. Adding in the numbers to the deflection calculator shows that my floor is NOT suitable for porcelain tile, but I have a few questions. I have 3/4" non-TG planks that I recently screwed down to reduce squeaks.

My joist dimension are as follows:

Spacing : ~ 15.5"-16.5" on center
Length: 11.5' with a metal IBeam and sistered joists spanning the middle of the room
Height : 7.5"
Width: 1.75"

The width of the room is 8.5' and total length is 23'. I've attached a few images for reference.

The plan is to add 3/4" or 5/8 plywood atop the planks with Ditra and porcelain tiles. Is this doable? Thank you so much!!
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Unread 06-09-2021, 08:31 AM   #2
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Hi Chibbo,

I don't think anybody here is going to guarantee that the floor would support tile as is, but just looking at the picture it appears to be sturdy. You could give it the "jump test."

You could also call Schluter, or just go ahead and sister the joists.
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Unread 06-09-2021, 10:59 AM   #3
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Welcome back.

Some confusion on my part.
Quote:
Originally Posted by Chibobo
Length: 11.5' with a metal IBeam and sistered joists spanning the middle of the room.
The beam is in the center of the room to be tiled? The 11.5' span is on one side of the beam? The span on the other side is?

Which joists are sistered? I'm not seeing them in your photos.
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Unread 06-09-2021, 10:14 PM   #4
Chibo22
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My apologies! Here's a diagram of the kitchen so far. I may have mislabeled the amount of joists that are sistered. They are the thicker lines. I've also included some future plans for a bathroom in the basement directly below the kitchen. Though I am unsure of when this would go up, but i could always rough it in to help lower the span of the lower half of the kitchen.

The beam is evenly distributed under the kitchen so the span is equal on either side. The beam spans the entire width of the house with several support beams.
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Unread 06-10-2021, 09:13 AM   #5
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Little more help here Chibbo. The black outline in your drawing is all part of the new kitchen?
Quote:
Originally Posted by Chibbo
The beam spans the entire width of the house with several support beams.
I'm guessing you meant support posts rather than beams. Would that be correct?

The 11.5' measurement is the unsupported span of the joist and not the joist length? That is, the measurement between the support beam edge and the exterior support walls?

Do you find any sort of grade stamp on any of the joists? Something to give a species and grade of the wood?
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Unread 06-10-2021, 10:39 AM   #6
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Yes! Support posts, my apologies. The black line represents the exterior shape of the kitchen and house ( the remainder of the house is on the right hand side, I didn't include it in the image other than the staircase. The staircase has additional support joists surrounding it, as seen from the basement)

I'll have to confirm wether 11.5 is the fully unsupported length, i measured from the wall to the inside of the support beam, would that be correct?

I'll also check for stamps today and report back.

Thank you!
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Unread 06-10-2021, 12:46 PM   #7
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That measurement would be the correct one for purposes of evaluating your joist design deflection.

The connection, or lack thereof, of the joists over the center beam is also a serious consideration in your application, but let's see what your joist material is before we continue that discussion.

My opinion; worth price charged.
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Unread 06-11-2021, 07:38 PM   #8
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I looked but was unable to determine the wood used. There are no visible stamps. I took a picture of the wood up close.
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Unread 06-12-2021, 08:58 AM   #9
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Not enough of the lumber visible for me to make a accurate judgement of species or grade, but if your measurements are accurate I'm reasonably sure I can find you a span table that says your joist structure met the code required (USA) L/360 deflection criterion. Whether you're comfortable tiling over what you're got is entirely up to you.

The biggest hazard I see is the joist splicing over the center beam. without those joist ends being very well fastened together, you can get a very substantial uplift at the joist end there when a significant load is applied to the center of the unsupported span on either side. You want at least to ensure that the plywood you must install over the board subflooring does not have any joints directly over that area.

My opinion; worth price charged.
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Unread 06-13-2021, 07:12 PM   #10
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Thanks for the responses CX, really appreciate it. How would you recommend fixing the two joists together? I'm also planning on adding several joist struts as seen in the photo attached.

If there are any other photos that would help identify the wood I can do my best.

Thanks again.
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Unread 06-13-2021, 09:42 PM   #11
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The best way to fasten those joist ends is to use construction adhesive and mechanical fasteners when they are installed. That ship, of course, has sailed. Adding some decking screws at this stage can help.

If you're talking about the cross-braces I think I see in the photo, save yourself some work. Those will not improve your joist deflection at all.

Someone else might give you an opinion of your joist species. The only thing that might help in that arena would be photos of more of the material. A grade stamp would be far more helpful. Technically, the only way to determine the grade of the piece is to see both sides of the entire board. It would take at least more of several for me to even hazard a guess.

My opinion; worth price charged.
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Unread 06-21-2021, 12:23 PM   #12
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Thanks CX! I'll look into fastening those two joists together wherever I can.

I remeasured the unsupported spans yesterday and I was initially off by a few inches. Both unsupported spans are 11.1' and 11.3'. Would that drastically affect the deflection?

Based off all this information, would tile be ok? I'm looking to go ahead with something and I have to make a decision between porcelain and wood asap.

Thank you for your help thusfar, it's unfortunate I could not find any mill stamps.
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Unread 06-21-2021, 01:46 PM   #13
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It would make a difference. Again, I can almost certainly find a span table that says your joists meet building code, which makes them sufficient for a ceramic tile installation. Can't make them fit our calculator, which is more conservative. Up to you what you're comfortable tiling over. With the addition of a properly oriented plywood layer over the sawn boards, I'd likely install ceramic tile. See my warranty information below.

Potential cracking in the vicinity of the beam is still a consideration.

My opinion; worth price charged.
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Unread 06-21-2021, 08:27 PM   #14
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I'm no tile expert...

But it looks like your floor is marginal, with 2x8 joists over a 12' span. That's a L/D of 300 and you require 360 for tile.

But I'm also concerned about tile over the I beam - Especially with 2x8 joists. Wood creeps and sags over time. You see it in all the older homes... joists in good condition regularly sag by 1/2" or more over a few decades.

If tile was only over the span of a single joist, the entire field of tile would be in compression if the joist were to sag. Less risk of cracking since ceramic materials are strong in compression. In tension, ceramics crack. The area over the I beam will see tensile strains, both from live loads and stress over time.

When I did my kitchen, which was also 2x8 over a 12' span, I sistered.. glued and screwed all the joists and then installed TG 3/4 ply perpendicular to the joists. It really wasn't expensive or labor intensive considering the overall project.

If I was tiling over an I beam.... I'd probably sister all the joists and add an additional 16' 2x8 over the I beam. Might be overkill but I'd rather spend 10% extra time upfront then have to tear out a kitchen later.
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Unread 06-21-2021, 11:32 PM   #15
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Quote:
Originally Posted by Jason
But it looks like your floor is marginal, with 2x8 joists over a 12' span.
Quote:
Originally Posted by Chibbo
Both unsupported spans are 11.1' and 11.3'.
Jason, there is a substantial difference in deflection between a joist spanning 11 feet 4 inches and one spanning 12 feet. Most residential building code would allow me to span your 12 feet with #2 SPF in nominal 2x8. And the ceramic tile industry permits ceramic tile installation over any wood framing that meets building code, which is also L/360.

Would it be my favorite? No. And I'm more concerned with the area over the support beam than the overall joist deflection, but I'd still be inclined to add plywood, a suitable tile substrate, and ceramic tile if that's what I wanted.

My opinion; worth price charged.
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