How can I stiffen a bouncy floor? Will another layer of 3/4" OSB work?

Question

It's an unfinished room above a garage, 2x10's at 12" oc spanning 16 feet, and it's very bouncy. I have extra 3/4" OSB I was thinking of putting over the existing. Will this do anything or do I need to beef up the joists from below?

Answer 1

2x10 spanning 16 feet sounds like it maybe on the edge of what is allowed.

Since they are 12"oc I'd vote for beefing up from underneath.

Can you install a beam between posts that will cut the span in half?

Eric

Answer 2

You may be able to strengthen the floor joists by adding another 2x10 to the existing member. These can be nailed in place and may give you enough rigidity to solve your problem without ruining the garage space with posts.

Answer 3

You need to "sister" on deeper, wider joists and possibly re pull the electrical wires. Adding more weight will not help. There may also be  possibilityy of adding a wall to wall flush beam of greater width and going wall to wall in the center if you don't mind encroaching into the garage ceiling a bit at center span. You must then support the center cut joists from both sides of the cut.

Answer 4

added more weight , another layer of 3/4" will make it worse, probaly cause it to sag over time if it is already bouncy.  Like all the other answers, a lot more structural support underneath is the only option.

Hmmmm,  you can place a couple of poles centrally underneath in the garage.  Is your garge a two car garage and able to have 2-3 poles in the middle?  This would be the quickist and easiest method whilst still complying structurally.

Answer 5

You need to beef up the joists from below.  If something is not supporting the floor, then putting more flooring on it won't help.  You need to support it better.

Answer 6

more support under the floor is the first step.. then add additional osb

Answer 7

2X10, 12" OC should be fairly sturdy on a 16' span.  Well within code requirements for a living area.  Keep in mind that while the room may be 16' wide, the span is measured between the supports.  The span on this type of roof is usually considerably longer than the room.

Adding OSB to the top will do little to help your situation if the floor is bouncy.  If it is spongy between the joists, the flooring may be to thin in which case another layer will help, but I don't think that is your complaint.

The best thing you can do to help this situation is to add blocking between the joists.  If there is not any blocking or bridging in place now, this will help bounce and vibration considerably.  If you have access to the joists from below, this is not expensive or difficult.  If you don't have access from below, it may be worth it to pull up the existing floor, install blocking and use your 3/4" OSB for a new floor.

Blocking should be perpendicular to the joists, at least one row middle of the span.  Cut the blocks to the width between the joists so it is snug, nail in securely.  You can offset the blocking 1 1/2" from joist to joist so you have room to nail from the ends.  The row in the middle is very important, that is where most of the movement occurs.  If you want more than one row, install the another row on each side of the middle run, mid way between the center and the supports.

Also, if you do take up the floor to do this and put the OSB down, make sure you glue it as well as nailing.  This will help stiffen the floor as well.  It would not help to glue the OSB on top of your existing floor -- it must be nailed to the joists to have any effect.

If the bridging is not in good shape, that is certainly the place to start.  The bridging must be tight to be effective.  Sheathing the bottom of the joists may help as well, but the effect of sheathing on the bottom will be greater if the bridging is in good shape.