Cross bracing floor joists

[Bill Dufour]

I thought floor bracing was a western thing for sesimic rollover prevention. Supposed to be the outer three joists. and then in groups of three.
Bil lD

[Mark Bolton]

If possible a simple fix that can greatly stiffen your floor without the work of cross bracing after the fact is to simply attach a band/bands of strapping or furring strips to the under side of the joists butted tightly together and running continuously from sill to sill. The cross bracing stops the joist from rolling slightly as it deflects. When the joists roll a a little bit the floor deflects and acts like the skin of a drum. You'd be shocked at how much a single run of furring down the center of a span will stiffen a floor. Its pretty impressive. If your span is of any length you could run two but it'd have to be a long span to make it worth while. We always just ran them straight down the center.

Its pretty common with tall I-Joist/long span floor systems to get some bounce in the floor and adding that single run of strapping will make the floor feel like concrete.

[Bill Dufour]

If possible a simple fix that can greatly stiffen your floor without the work of cross bracing after the fact is to simply attach a band/bands of strapping or furring strips to the under side of the joists butted tightly together and running continuously from sill to sill. The cross bracing stops the joist from rolling slightly as it deflects. When the joists roll a a little bit the floor deflects and acts like the skin of a drum. You'd be shocked at how much a single run of furring down the center of a span will stiffen a floor. Its pretty impressive. If your span is of any length you could run two but it'd have to be a long span to make it worth while. We always just ran them straight down the center.

Its pretty common with tall I-Joist/long span floor systems to get some bounce in the floor and adding that single run of strapping will make the floor feel like concrete.

Like the rat boards on a roof. No need to butt joint. Just overlap across two joists. I suppose even one joist side by side may work..
Bill D

[Jim Becker]

I thought floor bracing was a western thing for sesimic rollover prevention. Supposed to be the outer three joists. and then in groups of three.
Bil lD

It's required here, too...stabilizes for flex, especially since spans tend to be longer these days than "back in the day" because folks don't want posts and bearing walls in the middle of things.

[Mark Bolton]

We have come behind many "properly sized" engineered floors that were well suited for a bottom band. Engineered floors (and any floor) that are frequently pushed to their span limits can have a resonant frequency to them when someone is walking across that will actually make people disoriented and nauseous but they are completely within spec and deflection limits. The simple strapping trick on the bottom side turns the floor into a rigid mass. Its akin to a mini torsion box. I never would have believed it until the first time we did it. Its truly impressive. I dont think I installed a dimensional floor joist in the last 10 years of my time in the field and we used that trick exclusively. Its WAY faster than cross blocking or bridging between joists and it eliminates a million fasteners which are all potential squeaks. A floor that doesnt move doesnt squeak whether its screwed, nailed, glued, or any combination.

I will take a single run of furring from sill to sill over any form of cross bracing any day.