Floor Joist Reinforcement Question
 

I want to reinforce the main level floor in my house by installing sections of 2x10 between the floor joists from underneath. My basement is unfinished so the joists are exposed. I don't have support pillars in my basement as the house is supported by an iron I-beam to meet the code requirement, but this minimum code is not enough and I get too much bounce in portions of the floor. My plan is to run two lines of 2x10 along the length of the floor, each line being half-way between the wall and the I beam.

My question is this - would I achieve greater reinforcement by installing the 2x10s parallel to the floor joists/I beam? Or would it be stronger to "box in" the open section of floor by installing the 2x10s parallel to the floor at the bottom of the joist opening.

Thanks for everyone's input.

how long is the span between the i beam and the wall?

I had that problem in a rental. How long is the span? why not a strategically placed Lally or 2 on a crossbrace spanning a couple joists?

X2

Installing solid blocking from wall to wall will stiffen up a bouncy floor system.

I did this in my own home. Blocking in mid span on the floor joists should be installed on edge perpendicular to the floor joists mid span. So in my case I installed 2x10 on edge to the 2 x 10 floor joist. Cut them tight and pound them in and toenail them with something smaller than 16 penny nails...about four on each side of each end of the block.

This stiffens by bringing five or six joists into support of a point load such as a person walking.

It did a very good job for me.

We did it at my mom's house too with good results.

I doubt you have taken into consideration my Brother-in-law...6'8", 375lbs of dense inertia. May G-d protect you from such a fate as having him clomp about on your floors!

Thanks for everyone's input. The span is about 12 and a half feet from the I beam to the concrete foundation wall.

Tom, if I am reading correctly, you are suggesting I box it in at the bottom of the floor joist, so the 2x10 is parallel to the subfloor?

Carleton, I'm not sure what a Lally is. I'm a bit of a novice with framing.

Thanks again.

Here's a good tip for the required depth for joists:-

Measure the span length you wish to bridge in meters. If you double that number that is roughly the depth you need in inches.

For example a 3.5 meter width would need about a 7 inch deep joist. Buy the next size up and you're gonna be alright.

Tom is suggesting that you insert a piece of same sized joist material in between the floor joists, perpendicular to them, and in the middle of your span. This means that for a standard 16" on center floor, your pieces of blocking will be 14 1/2" long, although you should measure each one separately in order to get the tightest fit and maximum benefit. The blocking, when installed, will essentially act as a joist running perpendicular to the current joists, without taking up space below the existing framework. If that solution does not give you the support you need, then you will likely have to go to a strongback design, with a beam running under and perpendicular to the floor. If one of your questions was whether to run any of your framing with the narrow (2) side vertical and the wide (10) side horizontal, the answer would be no. Lumber should always be utilized with the wider dimension run vertically.

Perfect. Now I understand. Thank you.

And thank you everyone for your input.

Here in the Galveston area, where most of the houses are built on stilts, "lally" columns are generally considered to mean "jack posts" like such:

http://www.marshallstamping.com/jack_posts.html

which are prohibited here for some reason, altho back home in New Hampshire people use them like crazy. What is legal here, are adjustable columns:

http://www.marshallstamping.com/steel_columns.html

I have a room that was once a porch, I'm fixing to put in a row of those under the house to support it better.

I claim to be a carpenter but had not heard the "lally" term either. But that was a thought I'd had, posts under the shaky areas, that is. I did it once in a crawl space - my clients complained that their washing machine would shake the whole damn house on the spin cycle. I put pillow blocks under the area of the two front corners of it (the back was up against the wall and covered by the foundation, taken care of by it rather. I ran a 4x4 under the 3 joist bays in question and dropped 4x4 posts down to the two pillow blocks. Made a big difference.

But posts in a basement can be more trouble. Blocking tween the joists as described above would be good, I'll agree. If you want to go overkill, use some of the newer polyurethane const. adhesive with them, but wear rubber gloves when you use it. If head space in the basement is an issue, you might try 4x6s or 4x8s instead, to run under the joists, perpendicularly. If you go 4x6s you'd still need more of them to equal what 2x10s would do.

Never heard of a Lally column?? or as most guy's call 'em, lolly....What the hell do they hold houses up with out there in California??

The glue would not give any extra strength, the strength is derived from a tight fit, top to bottom, across the joist. This prevents deflection of the joist, which prevents sagging. As glue typically can be compressed more than wood, it could not possibly function as well as custom fit blocking which is tight. I have seen people use multiple rows of blocking as well, in high traffic areas.

California carpenters must not be real men, because any real man knows what a lally column is. Once your testosterone reaches the certain level, 'lally' automatically registers in your brain.