Floor bounce joist sistering

joehomeowner

I have a problem with floor bouncing. I have 2x10s with a span of 15ft 16” on center. I would like to finish my basement and I’m afraid the bouncing will crack the drywall and/or I would just like to fix the annoying bounce. I’m looking into sistering the joists. I can’t get a 15’ 2x10 down into my basement maybe 10ft at most. Can I use two 8 footers glued and nailed to the original joist then a shorter piece over the joint. Would a 10 footer attached mid span work as well? Would an I-beam be better than wood? How would I attach an I-beam to the original joist?
Thanks

Wildie

I'm not a carpenter by trade, but my thought would be to sister 2X8X10's to the 2X10's. Centered, leaving 2 1/2 feet at each end, open! Two 8' would allow flexing in mid span, just at the point where stiffness is most important! I'll be looking forward to seeing the comments from our expert members!

joehomeowner

Thanks for your comment. Would it buy me anything to also put the 2.5ft pieces at each end? What combination (s) of lengths or materials would be best? I’ve read about someone using steel or manufactured wood I-beams? Wood I-beams are lighter and would be easier to carry. I just can’t get a 15ft long board down into the basement.
Any thoughts would be helpful!!

Wildie

I doubt that a filler at each end would be of much good! One thought that I have had since, do you have any cross bracing (X) in place right now! You should have two rows of these, 5 feet out from the walls! Its amazing how X-bracing will stiffen a floor.

buletbob

say Joe! what type off floor bridging do you have installed?? is it continuous between all beams right to the foundation or girder???. and also what is the finished floor above. that floor beam is rated at 15'- 2" for northern Fir. I would check the bridging before doubling up the joists. even put two more rows in if need be. BOB.

joehomeowner

My basement is about 30ft across with a steal I-beam down the middle. The one half of the basement is below the family room where I notice the bouncing or give in the floor. The finished floor is carpet. There are cross bracing (x) (floor bridging?) between each joist about 5 ft from the one end near the steal I-beam. This is where the most foot traffic is above. Does x bracing really help the flex? One person I asked about x-bracing said that it does little to help flex or bounce it’s there to keep the joist from twist. I have also seen were people use solid wood 2x10s between the joists. Which is best X or solid wood? How many would be best??
Thanks!!

buletbob

what type of bridging do you have wood cross bridging or is it metal cross bridging. the solid blocking would be your best bet. the bridging DOES help to support the floor. when the weight of the floor above is pushing down the bridging will help the floor joist from deflecting down and from having the bottom of the joist kicking sidewards. by installing the bridging you will dispurse the weight to the surrounding floor joists.

joehomeowner

The x bridging is wood pieces approx 1x 4 stapled in place. If the solid blocking is best then that’s what I will go with. I may have to run some wires through since I’m adding recessed lights.
Thanks for your ideas

buletbob

try nailing the bottoms of the cross bridging tighter to the floor joist hammering them in a upwards direction. with the wood shrinking over the years from first being built they will loosen up as why I don't like using the metal cross bridging, I have witnessed the metal pinging as you walk across the floor.
I personally would do three rows of bridging on a 2x10 15' span ,its over kill but for an extra 20 minutes a tighter floor will be appreciated. BOB

Wildie

I like cross bracing, rather than solid blocking because downward movement of the floor is transfered across the diagonal brace to the bottom of the adjacent joist, therefore the weight is transferred to both joists on either side. Whereas, blocking is pulling on the side of the adjacent joists. X bracing does prevent twisting of the joists also! And I do agree with 'buletbob' about placing 3 rows of bracing! I would also suggest that the bracing would be screwed in place, rather than stapled! This may account for the limited advantage of your existing bracing!

ponch37300

What kind of windows do you have in your basement? You should be able to get 2x10s in from the outside threw the windows. I have done this with ceiling grid before.

joehomeowner

None, there are no windows and the stairs is finished with a 90 deg bend.

ijs12fly

Joe, Here is a great article. The metal strapping may be your easiest solution.

http://www.taunton.com/finehomebuild.../021184090.pdf

I too have joist issues but my concern is cracking a travertine floor.

Do you have space below the joists? If so you can make an upside T with a 2x4 or 2x6 and really strengthen the joists.

joehomeowner

Thanks for the link - good stuff! I was going to finish the basement so I was trying not to reduce head room any more than it is now 7' 8". The pdf shows gluing and nailing 2 layers of 8ft plywood and overlapping the seams. Is this article using plywood because it has better strength or just easier to work with?

Nestor_Kelebay

Ijs12fly:

I'm assuming you mean and "upside down T with a 2X4 or 2X6..."

If so, can you link to any online literature on doing that?

I graduated as a mechanical engineer, and doing exactly that makes perfect sense to me, but I've never come across any technical articles on it. What I have come across is people saying "Nope, you can't do that. I've worked in the business for 600 years, and every beam strengthening design I've ever seen involves adding wood to the SIDE of the joist, never the bottom of the joist. Ergo, it won't work."

It's like beating your head against a wall trying to get that person to understand that if the wood you add is as strong as the wood the beam is made of, and you use a glue that make a joint that's as strong or stronger than solid wood, what you have is a stronger beam.

But, there is a certain wisdom in knowing when to quit arguing.

__________________
Bashing my head against the walls in some of the internet's finest chat rooms.