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Old 11-30-2010, 09:08 AM   #1
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Bouncy i beam floor


main floor really bouncy in my 15 year old home. Open underneath and has wood ibeam joist construction, approx. 20 foot span with no supporting columns.
What would be the best approach to "stiffening" or "dampening" this floor. I am concerned about marrying or sistering to this engineered beams as that may effect their intended design.

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Old 11-30-2010, 09:22 AM   #2
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Bouncy i beam floor


In no particular order of recommendation, standard remedies for your situation includes some or all of the following
1) Addition of a beam and quash blocks at appropriate locations
2) Blocking
3) Sheathing the bottom of the TJI's with nominal 1/2" material

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Old 11-30-2010, 09:39 AM   #3
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Bouncy i beam floor


If I were called in to do that job and it was a crawl space under the floor I would install a drop girder with supports at 8 foot centers.
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Old 11-30-2010, 10:28 AM   #4
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Bouncy i beam floor


Quote:
Open underneath and has wood ibeam joist construction, approx. 20 foot span with no supporting columns.
Ayuh,... Put supporting columns in the centers,... Problem solved...
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Old 11-30-2010, 05:29 PM   #5
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Bouncy i beam floor


If you don't mind the beam in the middle like Bondo said, it is cheap, fast, and will kill the problem. The other suggestions will do, too. You could also cut 1/4" (or thicker) plywood and glue/nail it to the joists to box them; stagger your joints on opposite sides, and get 10' plywood if available. Myself, if I did this, I would try two, ten(or 8) foot pieces on one side and a centered, 10' (or 8) on the other side. You're just looking for a boost, not full support. Many ways to do this. j
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Old 11-30-2010, 05:57 PM   #6
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Bouncy i beam floor


If you add center blocking, do not nail through the main span joist top/bottom chords to fasten, toe-nail instead.

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Old 11-30-2010, 08:04 PM   #7
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Bouncy i beam floor


If the bottom of the joists are not drywalled, they should have minimum 1x3 strapping, not more than 8' spacing, perpendicular to the joists.

Solid blocking, cut to fit snugly between the webs will also help to stiffen the floor.

Whenever I do I joists, I use 1x3 or 4 cross bridging, stapled with medium crown staples, into the joist flanges. This will help with the bounce associated with long spans on I joists. I like to put 2 rows of X-bridging, 4' apart, centered mid span of the joists.


When walking across a floor, joists with large spans will deflect independantly as you move. Bridging helps to unify the joists and make them work together, as a system.

Strapping the bottoms will have a similar effect.

I was goofing around one day and decided to do a mock floor system, using only wood X-bridging to support the floor. No end bearing on the "joists". I then loaded weight in the center of the floor, to show how bridging provides load sharing across the assembly.
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Old 11-30-2010, 08:06 PM   #8
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Bouncy i beam floor


couple more.

The first pis is before the bridging is stapled and the box is attached. The second is after stapling the bridging. Remember, the bridging is providing all the support at this point.

The box is nailled into the end joists only. It is not providing any support to the field joists.
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Bouncy i beam floor-001.jpg   Bouncy i beam floor-003.jpg   Bouncy i beam floor-009.jpg  

Last edited by loneframer; 11-30-2010 at 08:09 PM.
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Old 11-30-2010, 08:13 PM   #9
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Bouncy i beam floor


Excellent display loneframer.
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Old 11-30-2010, 08:16 PM   #10
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Bouncy i beam floor


I had 270 lbs. on the center joist before the assembly failed. The staples pulled through the 1x3 strapping, which had been laying outside of my garage in the rain. Normally, I would use 1x3 or 4 pine, which would have easily held much more weight before failure.
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Old 11-30-2010, 09:00 PM   #11
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Bouncy i beam floor


Very informative pictures to illustrate the point, and another route to stiffen a floor. Instead of stiffening parallel to the I joists, you are building trusses perpendicular to them, as well as spreading the load from one joist to its neighbors. I think blocking has the same effect, but with more wood, no?
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Old 11-30-2010, 09:53 PM   #12
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Bouncy i beam floor


Quote:
Originally Posted by jklingel View Post
Very informative pictures to illustrate the point, and another route to stiffen a floor. Instead of stiffening parallel to the I joists, you are building trusses perpendicular to them, as well as spreading the load from one joist to its neighbors. I think blocking has the same effect, but with more wood, no?
Blocking will have the same effect, as well as add a level of fire protection in enclosed ceilings.

Here's why I prefer X-bridging.

When using conventional lumber, I fasten the bottom of the bridging as soon as the decking is completed. As the lumber shrinks, the bridging actually tightens itself against the joist, making an even stiffer assembly over time.

Wood blocking has the potential to check as it shrinks, which can lend to squeeks in the floor, not to mention, it's hard to fit blocks snugly if the joists are cupped or twisted slightly. In addition, I have seen block after block hammered out by mechanical trades to make way for equipment, pipes, wires, etc.

With X-bridging, more often than not, it won't pose an issue with tradesmen.
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Old 11-30-2010, 09:56 PM   #13
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Bouncy i beam floor


Thought I'd throw in the destruction after catastophic failure.

As you can see, the staples didn't pull out, they pulled through the bridging.
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Old 11-30-2010, 11:16 PM   #14
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Bouncy i beam floor


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Originally Posted by loneframer View Post
In addition, I have seen block after block hammered out by mechanical trades to make way for equipment, pipes, wires, etc. With X-bridging, more often than not, it won't pose an issue with tradesmen.
That is certainly a big benefit. A long-time home builder once told me that he almost quit finishing on a job when some plumbers showed up with a chain saw to work on the lower level. He said what they did to his nice, 2x6 walls nearly brought him to tears.
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Old 01-19-2011, 02:15 PM   #15
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Bouncy i beam floor


If i wanted to "stiffen" the wooden i beam, how would I do that?
Could I add 3/4"plywood in 8-10' strips and glue and screw to the upper and lower elements of the i beam or should the plywood go in the area between the upper and lower support elements of the ibeam?
FYI, I do not want to use lally columns, etc., structure is stable just noisy

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