Our house is 1.3 yr. old and we're not happy w/ the bounce in our first floor kitchen. Floor joists are 2x10s on 16-inch centers over a full unfinished basement. Joist length is 13.5 ft. Wood X braces between joists were installed at 7 ft. What's the most cost effective way to stiffen the floor? Would installing additional 2x10 blocks between joists help or should a 2x12 be nailed to every other 2x10 joist?

Kimosher

I personally use a rule of 2 feet over the intended dimensional lumber used. That means, for a 2x10 joist, I would span 12 feet without noticeable deflection (bounce) regardless of what specification loads say.

The engineered I-joist are now the most popular for a solid floor system and can span much further than conventional KD lumber.

2x12's are no help because they won't fit over the plates and headers unless you notch the ends and then they are no longer 2x12's.

Instead, if possible, add 2x10's so that you have 12" o/c instead of 16". If wiring and plumbing prohibit this, then try to double up as many joist as you can and use 3-5/8" ledger lock screws to secure them together instead of nailing.

Alternative is to add an additional support underneath.. good luck.

To get the deflection "bounce" out of the 2x10's first you must jack each joist up in the amount of deflection you have...then sister(attach)2x12's to the 10's. When you let off the jack your floor shoud be level. I would check the span tables for yellow pine 2x10's there's probably 1/8" varience in deflection. Nothing structurally wrong...but does bounce a little. If its a raised house cast iron post piers are also and easy solution if placement is permittable.