Tgi Framing

Tim Garrison PE

Yes, I would agree that well-installed x-bracing would share the load around and cause the joists to work together. Regular old blocking, not so much.

It seems like a lot of work to mess with all those x-braces. A good floor diaphragm also spreads the load. And we're only talking a few % stiffness increase either way. Why not just design the floor joists stout enough so that no bracing is required?

neolitic

I understand that in theory it isn't
statistically significant.
What we are telling you is that long experience
in the real world says it is a noticeable difference.

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loneframer

I see your point and it may well be the case. However, I have framed many homes that are either basements or crawls and they don't get rocked right away, if ever. As for the ceilings that do get rocked, I feel more comfortable knowing I've done the absolute best I could do to make it a better floor assembly. It takes me about 3 hours total to bridge an average 1600 sq. ft. floor. That includes cutting, installing and bottom fastening. The rockers love it because the joists stay straighter between framing and hang time. I always straighten the joists while decking and the bridging pins the bottoms straight.

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Timuhler

Again, I'm not arguing this point or any point in this thread. What I'm trying to do is reconcile real world experience vs available data.

For instance, in a floor that your or Lone are talking about, does the bracing mean there is 1/2 as much vibration? Did it vibrate 1/8" before and its now 1/16"?

Would adding furniture do the same thing? In my dining room, which is I-joist, you can hear things moving in the china cabinet. But I don't feel it. It is about 10' deep x maybe the same wide. Would adding 1 row of cross bridging get rid of the sound of the china cabinet?

The data that I'm finding show that first off, the right size joist should be used to the "feel" we are shooting for. I-joists are typically designed this way, for a stiffer feel.

2nd to that is that if we are constrained to a design that will bounce more, what is the most effective way to deal with this? It appears from the data that adding strapping is the best way, and arguably faster.

This is a good topic. Its getting the wet brain cells to move a little

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Warren

Seems like to me what really occurs with the cross bridging is lateral stability. We all know that a joist is strongest when it is perfectly vertical. Tip that joist a few degrees and it will have less strength. To exaggerate this point, visualize the strength of a joist while it is laying flat. I agree whoever said that adding drywall creates a similar feel. This keeps the bottoms from moving and keeps them more vertical. I think the argument against the solid blocking not being as effective is due to the fact that no matter how well it is cut, it will not have 100% contact with the mating surface. The cross bracing on the other hand, will be in contact with the bottom of the joist where it is needed most. This same principal applies to rafters as well. I have seen where an engineer dictates that the chord of a roof is laterally braced with the sheathing.

I think the biggest problem with the drywall is that over time it will be prone to crack and move, thereby lessening its ability to work as a brace.

loneframer

The first time I saw a 300+ pound customer walk across a 2x10 floor with 3/4 T&G and metal strap bridging, I saw with my own two eyes that every joist his foot landed on deflected noticably, not to mention the sound of the bridging creaking under foot. Decided that day that metal was not the answer and that something else needed to take it's place, something like 1x3 pine or 1x4 if the price is right.

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Timuhler

We had a customer years ago, mid 90's or so. It was my job after school to screw off the floor just prior to carpet. He was a pretty big guy and he found a squeak after living there for about a year by his bed that drove him nuts. None of us could find the squeak. Finally Dave, my framing mentor, told him in a joking way (this customer had a sense of humor) that there is no squeak for the avg guy.

He laughed and told us don't worry about it.

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loneframer

Nearly every squeek I go to address is either gaspipe, plumbing or a central vac line rubbing in its hanger, or duct panning for the cold air return. Once in a while a guy will shoot into the red zone marked over a steel beam in the floor, but we usually catch them before we're done the framing. Hanger connections can pose some issues as well.

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Warren

Had a squeak one time that baffled me. Turned out it was caused by the pocket door attachment. The nail in the bottom shoe was creating a squeak whenever anyone walked by. That was the last time I ever used nails on the floor attachment. Screws from then on.

Tim Garrison PE

When I get called in to remedy overspanned floor joists here's what I try to do in order of preference:

1. Add support somewhere near mid-span if possible.

2. Sister every other joist with full depth joists, or if too much plumbing, wiring, etc., partial depth sistering is better than nothing. Certainly, every joist could be sistered but usually every other works fine.

3. Add depth to the existing floor joist by gluing and nailing a 2x4 flat to the bottom of the existing joists. At supports the 2x4 flat can stop - it doesn't need to go all the way (actually, the middle third of the joist is all that's necessary.)

4. I might try nailing a CS18 continuous strap to the bottom of the existing joists. Now the joist is a hybrid wood / steel unit with a bit better bending resistance.

That's it. I would not suggest blocking or bridging because it just doesn't do much structurally. But that's just one man's opinion.

UpNorth

Thank you, Tim. Good to hear from an engineer on this one.

neolitic

Science demands that you add some
and report back!

BTW:
Tim, I'm the last guy on the planet
who'd want to argue framing with you.

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Framer53

You starting a fight tonight?

Timuhler

So's yo mamma!

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UpNorth

"I understand that in theory it isn't
statistically significant.
What we are telling you is that long experience
in the real world says it is a noticeable difference."

That "noticeable difference" is all in the mind's eye, put there by the cross-bridger because it makes him feel good, because he did the work and "knows" it is right. Noticeable differences like this are what fuels the biz of those organ lengthening treatments one reads about in spam mail.

If there is a difference, please prove so with data. Engineers test things and have facts, and they live in the same real world as carpenters and builders. They may work inside a building and not outside, but they work nonetheless. They cooked up the elegant F150s that some drive, and those tools used by all. Theory, science, laboratory work, materials sampling, quality control, invention, product development. It is all work, too. Engineers are salt of the earth, just like carpenters. Furthermore, they are not all alike, just as carpenters are not all alike. There are good ones and bad ones in each profession.

Bridging may be required by some building codes if the joist depth is 6 times or more its thickness. However, it is usually not necessary if the joist ends are supported laterally against rotation and their top compression edges are restrained by sheathing or subflooring. Weyerhaeuser's engineers have worked their butts off to understand, develop, and improve engineered lumber products, and nowhere in their lit is there a call for bridging.

If you want stiffer floors, engineer the project with deeper floor joists.