Replies

1. 
   mike4244 | Feb 25, 2006 04:26pm | #1

   X bracing or solid blocking between joists might solve the problem. I imagine the joists are undersized for the span.

   mike

1. 
   jhausch | Feb 25, 2006 04:34pm | #3

   The joists are probably "properly sized"  - but they are finding that the allowed amount of deflection is too noticeable.

   Then again, it may be that the cabinet load was not considered by the folks that spec'd the floor.  Full cabs in the middle of a clearspan may not have been planned for. . . .

2. 
   jhausch | Feb 25, 2006 04:30pm | #2

   Assuming you have access to the underside of the floor:

   Start with blocking between the I-Joists

   You could then glue and screw 1/4 or 1/2 inch ply to the underside of the I-Joists to create a stiff "torsion box"

   I am sure others will have more suggestions, but blocking is the most common first step.

1. 
   txlandlord | Feb 25, 2006 06:15pm | #5

   Start with blocking between the I-Joists

   You could then glue and screw 1/4 or 1/2 inch ply to the underside of the I-Joists to create a stiff "torsion box"

   Ditto

3. 
   dieselpig | Feb 25, 2006 04:41pm | #4

   This sounds like one you'd be able to help with Boss.  Got a link to that essay on floor vibration you posted awhile back?

   View Image
4. 
   IdahoDon | Feb 25, 2006 07:25pm | #6

   There have been some good suggestions already. 

   I'd first start by checking how well the floor joists match the span.  The situation is probably marginal at best, especially considering there is a tile floor above. Personally, adding additional joists is the best route as it will help both the longevity of the tile above as well as eliminating the rattle.

   Then consider the situation between the exsiting floor joists.  If there are pipes and wires everywhere then adding additional joists is greatly complicated.  On the other hand if you're lucky enough to simply slip in the new joists then go buy a lotto ticket before your luck cools off. 

   Choosing between the better fix of additional floor joists vs. additional blocking and perhaps sheathing the underside is a cost/benefit issue that you'll have to decide on.

   If you go the route of additional blocking and sheathing and it doesn't fix the problem then you've greatly increased the problem.  Now you'd have to rip out everything you've done and install the floor joists. 

   Having said that, the torsion box effect of sheathing the underside of the joists is so effective that the shelves in my storage garage are built that way.  The shelves are 8' long x 2' wide with a single 2x4 on each edge and 3/4" ply on the top and bottom.  Supported only on the ends, a 700 lb load spread evenly over the surface barely deflects the shelf at all.  A 200 lb. person standing in the center deflects maybe 1/16"--very stiff.

   If a client's floor joists will span the distance with no more than L/240 deflection then I'd add plywood with blocking at ply seams.  Technically, if I weren't to bring the joists to this point before trying other options and the relationship with the client went south for some reason, they could have it inspected, showing that I didn't first bring the floor joists to a minimum code requirement.  

   "He said he'd fix my floor, but the inspection showed that he didn't even do the work required to meet basic codes, and instead spent all his time trying to look busy and steal my money."  "Blah, blah, blah--steal my money! Steal my money!"  Plywood, despite how effective, doesn't technically make an overspanned joist meet code unless an engineer will put his stamp on it.

   If you are going to sheath the underside of the joists, do it well.  Follow a nail pattern similar to a shear pannel--something like 8d nails every 4" and block all edges.  Springing the floor up slightly during installation would help to tension this ply and provide the most benefit, although for anything other than my personal house I'd pass on this idea since there is a tile floor above and it might crack grout or even tiles.

   Protect wires and pipes from the 8d nails by adding nail plates AND nail around these items as much as humanly possible by carefully marking locations on the ply.  Also make sure wires and pipes are well clear of the ply in-between joists as the joists will be hard to locate and the surface will get peppered with nails and screws when the sheetrock goes up.

   Some would suggest a thinner ply and do the entire underside of the floor, but I'd use 3/4" ply and cover 4' wide strips the length of the joists directly under the most obvious problem spots.  As soon as the rattle goes away I'd stop.  It may be that one or two strips are enough.  Heck, it might only take one or two sheets.  The rest of the ceiling can be furred out before sheetrock if that's in the plan.

   Cheers,

   Don 

   (edit)  PS  As sledgehammer said below, if the space under the floor isn't open finished space, then the beam in mid span is easiest.  Those of us who suggested the ply are assuming the headspace under the floor has to be left open with beams and colums not being an option.

   
   

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   Edited 2/25/2006 12:18 pm ET by IdahoDon

5. 
   sledgehammer | Feb 25, 2006 08:07pm | #7

   Reduce the span. 

   Add a beam.