Floor shake = Squeaky Floor?

I moved into a 25 year house (built in 1979) last summer which has hardwood floors throughout. While I love the hardwood floors I have a problem in several areas on the first floor with "floor shake".
On several spots, If I walk across the floor, there is excessive "shake" on other parts of the floor. For example, I'll walk across my dining room and the china cabinet which is placed againced the wall will will move (presumably up and down), enough to make noise. Same with the TV cabinet in the Family Room. But I can't ever hear the floor squeak.
My guess is that the subfoor in certain areas has pulled away from the joists causing this problem. Which is the same problem as squeaky floors, correct? Is this just an extreme example of squeaky floors without the noise?
This is a 1st floor problem only (why?) and the joists + subfloor is exposed. What should I be looking for to identify the problem from the basement? How do I fix it? Shim it or tighten it up with screws and such? There seems to be a number of solutions for squeaky floors these days... what's the best solution provided that it is indeed squeaky floors that I have? Thanks!
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The guys in this ng (myself included) are going to need a lot more detail to pin point the cause of this behavior
But w/o the info, IMO this is a problem of inadequate floor system stiffness.
It is different than the squeaky floor problem.
I'd guess that the floor joints run parallel to the wall that the china cabinet is up against. I'll bet that the TV cabinet is arranged similarly.
What size are the floor joists? what is their spacing? how long is the span (unsupporte length)?
Without knowing all the details, these ideas are just guesses.
If the hypothesis is correct, the solution is to stiffen the floor joints. The exact method of stiffening would be dictated by the details of the as built condition.
The fact that the floor is over a basement will make fixing the problem much easier.
You can search this ng for similar recent topics cheers Bob
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Have someone in the basement look carefully at the joists and subfloor for any movement while you make it shake, bounce on it. Simple sistering of new joists to old may be it. If joists are solid and it is the sub floor it will require some designing to to reinforce. It is probably the joists since the shaking is transfered far away.
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BobK207 wrote:

To add one thing to Bob excellent post, the reason the first floor is less stiff than the second floor is because the second floor likely gets a little help from the ceiling on the bottom of the structural members.
--
Joseph Meehan

26 + 6 = 1 It's Irish Math
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Ah... Sorry... Here's more information
2x10 floor Joists 16" on center, laid out as below, Hardwood floor , the span I'd say is about 15 feet., x represents wood cross bracing.
-------------------------------------------- x s -------------------------------------------- x -------------------------------------------- x -------------------------------------------- x p -------------------------------------------- x -------------------------------------------- x -------------------------------------------- x s --------------------------------------------
The hardwood flooring obviously runs up and down. A person standing in p can shake the furniture in s.
I have been in the basement with another person shaking the floor above and I really can't notice any movement. A coworker suggested that the cross braces (1 per span) is grossly inadequate ana a simple solution would be to add additional blocking as stiffeners as such...
-------------------------------------------- | | | x | | | -------------------------------------------- | | x | | | -------------------------------------------- | | | x | | | -------------------------------------------- | | x | | | --------------------------------------------
2x10s, circular saw and a framing nail gun should take no more than a day. I guess I'll try this since there's hardly any cost.
What kind of lumber should I use? 2x10s would be the best right? But wouldn't any stiffening member work including plywood? How far apart? How to get around plumbing + electrical wires? Cut notches in the blocking?
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Hmmm... 2nd time posting this... maybe it'll work this time.
--------------------------------------------- x --------------------------------------------- x S --------------------------------------------- x --------------------------------------------- x K --------------------------------------------- x --------------------------------------------- x S ---------------------------------------------
HW floor boards run vertical --- Joists, 2x10, 16" OC, 15' span x cross braces (a couple of anbled 2x4s) K 35lb kid bouncing here S shakes the floor here
A coworker is convinced that the cross bracing is not adequate and suggested additional blocking
--------------------------------------------- | | x | | --------------------------------------------- | I x | | --------------------------------------------- | | x | | --------------------------------------------- | | x | | --------------------------------------------- | | x | | ---------------------------------------------
Looks simple enough. I might try it since it won't be that difficult or costly. Should I...
Use 2x10s (same as the joists) or can I use other scrap lumber? plywood? notch out for pipes/electrical? nail or screw? I'm leaning towards a round head framing nailer.
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If the calcs I did are correct, cross bracing won't do s...t for your situation.

here is a link to a report that discusses this type of problem
http://irc.nrc-cnrc.gc.ca/cbd/cbd173e.html
taken from the report
"Studies of light joist (wood or steel) floors with wood deck, in progress at the Forest Products Laboratory at Ottawa, indicate that for spans up to 15 feet acceptable vibration performance for most residential occupancies is obtained if the static deflection does not exceed 0.05 inch under a point load of 220 lb."
also
http://www.inspectamerica.com/html/bouncing_floors.html
I calc that your joists will deflect ~.19 under a 220 lb point load or nearly 4 times more than desireable.
Maybe I made a mistake on the calc but the current floor behavior seems to agree with the calc.
cross bracing will provide little or no gain.
IMO you need to glue & nail (or screw) a 2x6 flat to the bottom edge of the existing joists and that will get you down to ~.07" (not perfect but much better)
Pre drill the 2x6 with a clearance hole do you get good clamping effect on the glue. I'd prop the joist slightly so the system is preloaded when you remove the prop. Wait until the glue drys.
cheers Bob
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I also say forget cross braceing. Get someone heavy upstairs and put a pole on the ground nearly touching the brace or a weighted string , put a ladder under the string and measure deflection. It is there.
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