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Old 01-04-2017, 02:21 PM   #1
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Shaky floor


Yes, it is another post about a bouncing floor, dishes rattling in the cabinets and vibrating nick knacks. Joist are 16 OC, 2x10, 14 foot span. One end of the joist are supported by a concrete outside wall, other end by a steel I-beam. Don't really know how thick the sub floor is but it is CDX plywood, and at least 16/32 thick. I suspect its two layers thick, well I hope it is.
Finish floor is laminate wood product of no structural value. We stretched a string across the floor, same direction as the joist, and observed a small gap in the middle, floor sags, of maybe 1/8 to 1/4 inch. The problem is when walking by the china closet the dishes rattle, which really hasn't bothered me but SWMBO wants it fixed. For the past few days I have read numerous postings about how to stiffen the floor and have tried x bracing and blocking with no noticeable improvement. Underneath the floor in question is a finished basement with a drop ceiling. I'm thinking the proper way to fix this is to increase the depth of the joist by gluing and screwing one of three products onto the present joist: 1) 2x12 SYP, 2) multiple layers of 3/4 CDX plywood with staggered joints 3) laminated veneer lumber. From the bottom of the present joist to the drop ceiling the distance is 9.5 inches which means I could have a joist 19 inches deep.
There is a complication, an A/C duct that runs under two of the joist under the china closet. Of course the duct is located pretty much center of the span. The duct is 8 inches in diameter. I will replace the duct with flexible ducting so the 8 inches can be squished down to an oval of maybe 4 inches in height providing a distance of 15 inches for additional joist. The duct supplies air to a laundry room. My questions:
1) Will adding joist depth of 19 inches eliminate dish rattling?
2) How much of a horizontal gap can be tolerated in the additional joist before performance is affected? There is a main A/C duct that occupies the space between the bottom of the joist and the top of the suspended ceiling. The duct is rectangular, 9x25 inches so there would be a gap of 25 inches in the added on joist. And the duct is again pretty much centered in the span. There are two joist between the china closet and the end of the main A/C duct.
3) Do I need to beef up all the joist in the room or only those under the china closet?

Regards
Jerry
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Last edited by JerryE; 01-04-2017 at 02:34 PM.
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Old 01-04-2017, 03:18 PM   #2
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Re: Shaky floor


Floor joists 14 feet long, 2x10 SYP construction, 16 inches on center, for a room rated 10psf dead load, 40 psf live load, have an l/d (length to deflection ratio) stiffness of about 400, which is generally considered adequate, unless you are putting down stone floor or large format tile.

There may be something else going on there, like a damaged joist, improperly attached subfloor, improperly supported joists. I would take a hard look at everything before I began sistering joists or adding additional depth unnecessarily. And if you do, I would only work on the area around the cabinet, since the joists appear to be adequately stiff as they are.

You may be able to put some rubber or foam under the cabinet, do NOT TELL your SO what you did, make it seem that you worked you ass off sistering joists, adding blocking, tell her anything but the truth, but at least try it first to see if it solves the problem. Or maybe put some rubber under the shelves at the supports, very thin, no one will notice, problem goes away. Just saying.

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Old 01-04-2017, 04:06 PM   #3
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Re: Shaky floor


Daniel I like your answer, shock mount the cabinet. I have a call in to my AC guy to come over to give an estimate on modifying the duct runs. Maybe once she sees the cost of that the rubber under the cabinet will not bother her. I looked carefully for a crack joist, nope, and not too many knots. I didn't see any adhesive between the top of the joist and the subfloor. which doesn't surprise me.
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Old 01-04-2017, 04:27 PM   #4
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Re: Shaky floor


See if she will accept rubber shelf liner.

This cushions the contents well, and usually stops all dish rattles.

Unless someone is playing Basketball through the room, it should work.


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Old 01-04-2017, 07:18 PM   #5
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Re: Shaky floor


Hi Jerry,

As Daniel said, that floor should be sturdy enough as a base for even a ceramic installation, something is missing. Are the joists grade #2? Your not-glued to the joists suspicion is concerning and not right, subfloors should be glued to the joists as you know. Is this the only thing? Beats me.

Rather than going thru the steps you mentioned, why not simply sister 2x6, 8 or 10" lumber to the joists? You can even laminate ¾" ply/OSB if you'd like. You can go the entire 14' length or at least the mid-⅔ span. Glue and screw or bolt. Jack up the center about ⅛" before installing. I can see 3 joists that should be easy, two you can sister both side, the 3rd one side. What do you think?

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Old 01-04-2017, 09:12 PM   #6
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Re: Shaky floor


Jaz man, those are some of my thoughts. That was one of the questions I had yet to ask, should I jack up the joist prior to installing. Glad you answered that. The AC guy said he would be here Friday, which Friday was not mentioned and it is not safe to assume here in east Tennessee that the immediate Friday was intended.
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Old 01-04-2017, 09:40 PM   #7
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Re: Shaky floor


I agree that jacking it up to re-level it, and sistering some narrower 2Xs in will be the best chance of stopping the shakes, but I interpreted the post as if you wanted to do as little as possible.

Which is why I suggested shelf liner.

If I mistakenly thought that, my apology, but raising the sag and reinforcing the joists is my advice too.


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Old 01-04-2017, 10:10 PM   #8
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Re: Shaky floor


I like shelf liner de-nagorg and that would work but the problem is what would the next owner do? Maybe they won't have a china closet or care about a shaky floor. The other option is to attach the china closet to the wall studs just off the floor. Let it float off the floor. I'm going with the added depth using 3/4 plywood glued and screwed on both sides of as many joist as possible then add some strapping to tie the bottoms of the plywood together.
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