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!

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

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.

BobK207 wrote:
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

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

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?

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.

If the calcs I did are correct, cross bracing won't do s...t for your
situation.

From a vibration point of view; 2x10's spanning 15' appears to be way
undesized.

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

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.