Floor joist cross bracing

I would say about 50% of the crawlspaces I inspect have cross bracing installed between each joist but never compleated. Meaning the top end was nailed but the bottm ends were not.
I have also observed that no twisting or movement issues were found and many homes are 20 years or older.

Would you consider this an issue after 30 years of no problems and would you recommend they be finished.

i use the Bridging comment from this whenever encountered, ymmv and others prolly have differing opinions


Thanks Barry,
Obviously after 30 years with no ill effects it should be fine but I will make a note of it.

Thank you. Nice one.


The bridging prevents rotation of the joist and helps distribute any concentrated floor loads to adjacent joists. While it may not have been a problem for 20 years, if the new owner puts a baby grand piano on that floor a problem could occur. So I agree with others you should mention the defect and move on.

Just returning in kind Barry :smiley:

I agree


you’ll catch on :cool:

me too, prolly…
you’ll catch on :cool:

you’ll prolly catch on ;~))

I agree with reporting the issue and moving on.

I would also explain during our post inspection meeting; that properly installed bridging belongs in the system and give several short explanations of what can occur if left untended.
Squeaking, twisting joists, possible nail lift, slight rolling floor plane and the age of the home relative to the floors condition so far.
Whats happened over time, if anything.

Would this be wrong in anyone’s opinion?:roll:
Thanks for any replies…Robert

No I would not consider it an issue or defect, even on newer construction. It’s considered good practice by many (myself included) to install blocking or cross bridging at 8’ intervals to help stiffen floor framing, but it’s only required for joists larger than 2x12 (nominal depth-width ratio > 6).

And you probably never will for typical framing with proper attachments to the sub-floor and headers.

JMO & 2-Nickels … :wink:

If the floor joists are heavy enough. They do not need cross bracing.

I agree with Randy, I have installed bridging in floor framing since the early 60’s, and it is required to provide a complete diaphragm for proper load support. In the post above, the builder forgot or was to lazy to crawl in and finish the job. It may have lasted this long, only because it was not required to carry the floor load if the framing was the right size for the span. It just went on to provide a floor that was bouncy and never had a concentrated load to accentuate a problem to the framing members.

it was nailed in before the sub flooring and when the sub floor was complete, you went underneath and finished nailing it.
It was not meant for rotation, but more for completing the diaphragm to make the floor system more stable and less bounce.
Any load imposed on the floor system is distributed equally rather than on just the immediate area.
I found this article that says the same thing.


Floor plans or specifications usually call for bridging between joists. Bridging holds the joists in line and helps distribute the load carried by the floor unit. It is usually required when the joist spans are more than 8 feet. Joists spanning between 8 and 15 feet need one row of bridging at the center of the span. For longer spans, two rows of bridging spaced 6 feet apart are required. **CROSS BRIDGING.— **Also known as herringbone bridging, cross bridging usually consists of 1- by 3-inch or 2- by 3-inch wood. It is installed as shown in figure 1-26. Cross bridging is toenailed at each Figure 1-26.—Wood cross bridging. end with 6d or 8d nails. Pieces are usually precut on a radial-arm saw. Nails are started at each end before the cross bridging is placed between the joists. The usual procedure is to fasten only the top end of the cross bridging. The nails at the bottom end are not driven in until the subfloor has been placed. Otherwise the joist could be pushed out of line when the bridging is nailed in.

No one is going to convince me that it is only required for higher depth joist.

Higher depth joist like bar joist, yes, rotation under load comes into play and the bridging is playing a double role.
Standard home floor framing is a different application. Nothing is going to rotate, it will bend and fail.
Higher web members in commercial or engineered floor joist, will rotate and fail. :slight_smile:

That is my experience, too, Marcel.

I will differ with that opinion James.
Hypothetically ( flooring systems ) are subject to loads the interacting structural components exert within the surrounding field.

Squash blocks and bridging are both needed.
Loads , be it horizontal or vertically placed in or on any given element within the field might play a roll in causing movement.
That is the reason for the bridging. The live or constant( dead ) load or loads are shared among the united field.
Nailing and the importance of a tight bridging all come together to act a one united field.
Code Reference: IRC 2003/2006, R502.7.1
NCA/TB/LTB Bridging

Just an opinion from years of education, observation and repair James.
A link to common carpentry terms.

Again I agree with you Robert. I have seen the results of no bridging in a proper designed house. The floor sagged in the center on both side of the beam. This was no wimpy construction either. The floor installers put shims under the sub floor to level it about 2 inches down. Moisture may have been a factor in softening the joists and sub floor but if bracing was put in at this location no movement would have occurred.:frowning:

Guys, bridging is for keeping a joist from rotating, not for transferring load. Sure some load can be transfered from one joist to an adjacent one thru bridging, but the amount of load transfered is next to nothing.

Old style bridging was often 1x3 or 1x4 pieces of lumber with the ends cut to fit the joists, with two small 6d or 8d nails thru the sloped cut end. Load would be transfered to an adjacent joist thru shear and withdrawal of those nails. And the wood is often split. The values are not even worth calculating they are so small. Anyone who has removed them (I have) knows how easily they come out.

Metal bridging is no better. It’s often a metal strap with just one nail at each end. And only one of the two straps in a typical cross pattern is effective in transferring load (the other one actually relaxes). So the amount of load transfered to an adjacent joist from each nailed strap is typically equal to the shear value for a single 8d or 10d nail. The newer claw-end nail on bridging is even less effective. Again, not even worth calculating.

JMO & 2-Nickels … :wink:

You are correct

Sorry James. Thank Mr. O’Conner.
Now if a barring wall is under the joist could not the load make the joist want to wonder? Or is the load going to keep it in place.
I am thinking this because a residential building is always under expansion and contrastive loads. Movement.
I am looking at the floor as a field not just independently.
Again remember I was field trained. Leaves a lot to be desired when you get the wrong foreman or carpenter to work with.
Thank you.
We called them St James Crosses.
Yes 2/3" or 2/4". Always built that way.
Just pulled this up.
Also, bridging is only required when the depth-to-thickness ratio exceeds 6 to 1, meaning bridging isn’t required by code on joists sized 2" x 12" or smaller.
Make sense to anyone. James?

When looking at the floor as a “field” or assembly one of the most important elements is the wood subfloor (e.g. plywood), and the attachment to supporting joists. It does so much more than transfer floor loads to joists, and is one of the most critical elements of a house structure. One of the other functions is to keep joists from twisting or buckling, and why bridging is only needed for deeper floor joists.

And good builders will usually glue-and-screw the subfloor to joists, whereas model codes only require nailing. Many glue-and-screw to prevent floor squeaks and possible call backs, but the benefits from a stronger attachment for the structure are huge.

See here … http://www.nachi.org/forum/f23/floor-joist-cross-bracing-63299/#post812570

That is why wherever joists are supported by a bearing wall there should be blocking between the joists directly above the wall

JMO & 2-Nickles … :wink: