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Old 03-20-2011, 02:14 PM   #1
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Floor bounce and vibration


I have a problem with floor bounce/vibration. Posted here once before and got some useful comments, done a little more research and want to post once more on the issue. It is hard to say whether it is more bounce/deflection or vibration but I think it is more vibration.

Here is the background. New construction, builder went bust. So we are kind of on our own.

36ft span in the basement. 2x4 supporting wall at midpoint. LPI 20 Plus I joists. Joists are 11 7/8 depth, flange is 2 1/2 wide, 16 OC.

Wish we had beam and post support as opposed to 2x4 supporting wall but we don't...supporting wall seems pretty tight to the joists.

Basement unfinished and open from below. Most of probem is on one side of the 36 ft. span (e.g. the 18ft span from support wall to exterior wall) where our family room and master bedroom are.

Wondering how to solve problem:
1) Add two rows of blocking.
2) Adding plywood or OSB to joists (sistering to the chords)
3) Nailing 2x4 or 2x6 perpendicular to joist on bottom of joist (kind of strapping).
4) Replace 2x4 supporting wall with beam and posts.

Don't want to add beam and post in other area of basement--some day may want to finish it out.

In particular I am wondering on whether option 1 or option 2 would be more effective.

Sorry long winded post...

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Old 03-20-2011, 10:12 PM   #2
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Floor bounce and vibration


I would suggest the blocking first.

It seems an odd thing that you should be sensing any deflection or vibration from the floor joist as you described. Those are big "I" joists.

Andy.

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Old 03-21-2011, 06:02 AM   #3
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Floor bounce and vibration


2nd on blocking, either 2x between joists or metal ties. For a 36' span. I would do at least 2 per.

Not sure I understand what you mean by 2x4 supporting wall????
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Old 03-21-2011, 08:37 AM   #4
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Floor bounce and vibration


I agree - 2 rows of blocking.
If you decide to add blocking - 2x8's? - do not cut any part of the existing
joists.
Install the blocking in every-other, "joist-bay" -
(use a High-Quality, construction adhesive - "PL Polyurethane" -
"pricey", but it works very well! - not knowing where you are, and
what's available - "Liquid Nails" Construction Adhesive or equivalent should
be useable - not "Panel Adhesive").
You don't want "floor-squeaks"!
Do not install the blocking, starting from one end of the room, and
continuing to the other end!! (bowing/deflection of the joists!).
Wait 1 or 2 days (so the adhesive sets).
Then, go back and install the rest of the blocking - use adhesive!
Keep the blocking away from the bottom surface of the sub-floor -
unless you use adhesive between the blocking and the sub-floor.
For the blocking - do not use "Treated Lumber" -
"S-P-F" is fine.
As far as the "2x4" supporting wall is concerned -
If it has a double 2x4 "top-plate" - you're probably OK.
(16 inches on center!)
If it only has a single 2x4 "top-plate"; and, the floor-joists above are
not resting directly (or close) on the 2x4's in the supporting wall -
consider adding additional 2x4's - directly, underneath the floor-joists.
Hope this helps!
Regards!
rossfingal
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Old 03-21-2011, 10:26 AM   #5
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Floor bounce and vibration


Hmm.

Since it's mainly one one end of the building, what's different at that end?

Are you sure the wall is tight to the joists? If shims will go, put them in and see if that tightens it up.
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Old 03-21-2011, 10:31 AM   #6
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Floor bounce and vibration


Thanks for the informative replies. Appreciate the paitence because I am not knowledgeable and am just trying to learn how to solve the issue.

Sounds like blocking is the way to go.

Andy Gump--that is my understanding that these are pretty hefty TGIs and spaced reasonably close at 16 oc. Not sure why the vibration. Floor guy says it is because the rooms are open concept above. We do notice it more on the side of the house that is open as opposed to the other side that is chopped up. (FYI subfloor is 3/4 T&G, not plywood some kind of OSB product, no squeaking, but still new construction).

JB--it seems that is most of the quality homes I have seen they have LVL beams and then those adjustable steel posts underneath for support. We do not have that. We have 2x4 wall underneath the joist at mid span--basically a wall that you would use to frame out a room. It was on the plan, I guess it is acceptable vis a vis code, probably not ideal.

Rossfingal, yes the supporting wall is double stacked on the top plate with 2 2x4. As near as I can tell the wall is tight to the joists--however I can only tell for portions of the wall, the rest of the area I cannot see because of duct work on both sides.

Rossfingal--the blocking I am thinkging of is actually a portion of the TGI that would go in the bay. My understanding is that this would be nailed not glued. Also it would go in every bay--there are 38 bays. I would only put it on the side of the house where we are having trouble but would put two rows--6 ft from the supporting wall and 6ft from exterior wall. I am in south bend indiana.

I called Louisiana Pacific--they made the joists, to see what they had to say. They were not of great help but they also said start with blocking.

Finally, is the kind of thing that I should get some kind of structural engineer to look at? I don't have any idea how to find an structural engineer, but appreciate comments if you think it is advised?
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Old 03-21-2011, 10:50 AM   #7
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Floor bounce and vibration


You can hire a structural engineer if it would make you feel more confident about a solution but in my opinion your house sounds like it is well within conventional construction techniques or better.

Andy.
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Old 03-21-2011, 10:52 AM   #8
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Pyper--
The problem area is more open concept. The less problematic side is more chopped up, there is also a staircase down to the basement and up to the second floor on the "better" side. The better side is not perfect, but acceptable to us. THe wall is pretty tight to the joists, in my novice opinion I think they did a pretty good job getting this tight. It would be tough to get shims in, could probably get some in very minimally.

The big caveat would be I cannot see how tight the wall is where there ductwork blocking view. Ductwork blocks a fair portion of it. However, if it is tight on ends of where there is no duct work I am assuming it is pretty tight where the duct work is.
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Old 03-21-2011, 10:57 AM   #9
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Floor bounce and vibration


Is there no Iron beam supporting the first floor?

A picture sure would help.



If it were me, I'd rent 3 jack posts.
Install a beam (or just 2 2x10s) from wall to wall directly in the middle of the issue area. Supported by 2x4s (underneath and on each side) on each end.

Jack the beam up so the floor upstairs is level, then intall the 2x4 supporting.

Again a picture would help.

Last edited by pjordan4477; 03-21-2011 at 11:00 AM.
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Old 03-21-2011, 10:58 AM   #10
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Thanks Andy, appreciate it, it is a little reassuring. Understand it is from CA, sight unseen but you are in the business and know more than I.
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Old 03-21-2011, 10:58 AM   #11
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Floor bounce and vibration


Quote:
Originally Posted by meature View Post
Pyper--
The problem area is more open concept. The less problematic side is more chopped up, there is also a staircase down to the basement and up to the second floor on the "better" side. The better side is not perfect, but acceptable to us. THe wall is pretty tight to the joists, in my novice opinion I think they did a pretty good job getting this tight. It would be tough to get shims in, could probably get some in very minimally.

The big caveat would be I cannot see how tight the wall is where there ductwork blocking view. Ductwork blocks a fair portion of it. However, if it is tight on ends of where there is no duct work I am assuming it is pretty tight where the duct work is.
This is a two story house? Makes me wonder if the structure is porperly supported.
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Old 03-21-2011, 11:29 AM   #12
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Floor bounce and vibration


Yes, you could use parts of the same joist material - done that.
What I meant as regards "adhesive/glue" -
use nails/screws as well as adhesive - of course!
If any part of the blocking is going to contact the floor above -
use adhesive between the top of the blocking and the floor.
Two rows of blocking would be fine.
Measure out from one of the walls and snap chalk-lines for
the rows of blocking.
When you install it, go every other space between the joists ("joist -bays")
- right down each row of blocking.
Do one space between the joists, skip a space, then do the next, skip a
space, then do the next space - and, so on down the row(s) of blocking.
Then, go back and add blocking in the joist spaces that you skipped.
Nails and/or screws - I would still use glue!
As regarding consulting a "structural engineer" - you're not altering
the structure - just doing an "upgrade" that the your local
"Building Code Enforcement" entity (municipal, County, city, etc.)
should have caught before a "Final/Occupancy" permit was issued.
Things happen!?!
Also, when you're installing the blocking - don't assume the spaces
between the joists will be same - measure each one individually.
It sounds like you have a set of the plans for your house -
check on the foundation plan and see if it shows a continuous
footing under the 2x4 supporting wall (underneath the concrete floor).
Regards!
rossfingal
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Old 03-21-2011, 11:44 AM   #13
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Floor bounce and vibration


Pjordan,

Yes, actually 1 1/2 story. That makes me a little nervous. Not nervous like it is going to collapse but the kind of thing that years down the road could cause problem--maybe?

A little more back story. I had the guy that did the floor and I guess kind of design the engineering of the house look at it. He is with the truss company. Unfortunately, this was so early in the process that I knew even less than I do now--so knew very little. Also since builder went bust I feel we have very little recourse. We are on our own. (yes we had liens on the house, builder was not paying a number of the subs, so we got stuck paying for some things twice, not an unreputable builder when we hired, building for 20 years, good reputation).

In any event, right above the 2x4 supporting wall there is blocking. However some the blocking had been removed from some of the bays to permit ductwork. He said this should not have been done. That some of this blocking was load bearing from the 2nd floor. He said the TGIs are not supposed to be load bearing. The blocking was such that it carried the load down to the supporting wall.

He said he could put in some 2x4s, that would run vertically from the supporting wall to the floor and would reestablish this support. It is only a portion of that blocking that is load bearing--maybe a 15 ft. span, but that is where the ductwork is they knocked out some of the blocking--you can still see the nails.

I don't know if this would have anything to do with the vibration, I kind of doubt it. I am planning to get it done for structural purposes. Kind of angry that we have to spend more money to get something done that should have been done right the first time.
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Old 03-21-2011, 12:05 PM   #14
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Floor bounce and vibration


Pjordan,
No iron beam. Just TGI's and 2x4 supporting wall at midspan of 36ft total span.

Rossfingal--thanks for clarifying. Sorry I do need the obvious clarified becuase of my lack of knowlege, but I understand clearly now on the install. Yes, plan says there is a footing under the 2x4 support wall.
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Old 03-21-2011, 12:14 PM   #15
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Floor bounce and vibration


@pjordan4477
Good point!
Even if it's "only" 1 1/2 story.

@meature
From what pjordan4477 brings up and the fact that they removed
the blocking from above the 2x4 bearing wall -
I would probably double-up the 2x4 "studs", in the bearing wall - all
of them (might be over-kill: better safe than sorry!).
Especially, if they cut ANY parts of the double 2x4 top plate!
rossfingal

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