Sheathing strength question

[wfopete]

Can somebody tell me why it is that builders & code say to place sheathing perpendicular to floor joist? I’ve heard it’s because when plywood was the standard in sheathing, the veneer would be applied in lengthways fashion requiring the sheathing to be laid perpendicular to the joist for strength. But now with OSB’s popularity, does that same structural integrity logic still hold true? Or is reasoning something else altogether?

 

[blkhonda1991]

the only reasoning i can see behind it is you are getting more structure tied together with that one sheet rather than 8' of structure joined you are only joining 4' if you run it parallel

 

[viper86]

there's still a "grain" to OSB, hence being called 'oriented strand board'. I would imagine that once you got below the outer surface, most of the chips and flakes primarily lie in the long direction. Don't know that for a fact, however. But blkhonda is right as well, you have 4 continuous spans of sheathing vs. 2, making it a bit stiffer as well.

 

[NUTTSGT]

the only reasoning i can see behind it is you are getting more structure tied together with that one sheet rather than 8' of structure joined you are only joining 4' if you run it parallel

I'd agree with this. Running it long ways with the joist you have a piece that is basically spanning 16"x96" vs 16"x48" running perpendicular.

 

[MrMark]

There is a strength axis marked on osb. The strands are oriented as noted above.

 

[wfopete]

I’m using Advantech sub flooring, I’ll look to see if it has strength axis marked on it. What should I be looking for to indicate the strength axis?

http://www.advantechperforms.com/dare-to-compare/product-testing.aspx

 

[ddawg16]

Flooring? Different reason....

If you place it parallel to the floor, you end up with more seams on top of a joist. You might want to check that building code because I bet it says to T&G (tounge and grove). With the t&g installed perpendicular to the floor joists, the t&g is what spans the spaces between the joists....thus it is much stiffer...if you don't use t&g, if you step on the edge of the OSB between joists...without blocking, it's going to give.

Additionally, you stagger the how you place the sheets....In other words, you don't just lay them all down together in the same line. One full sheet goes down...then the next one is offset by one half sheet.

In case your wondering if this is really important.....it is.....please don't ask how I know....

 

[wfopete]

Oh yeah, don't worry 'cause I be staggering 'dem joints!

 

[Falcon67]

If it's floor, install longways and use tongue in groove. If you don't use TnG, then best lay the long seams on the joists and you'll have issues on the ends even at 16" OC. I've got a whole bedroom floor of 1/2" ply not TnG installed longways, it's ****. Your carpet will last, oh, maybe 9 months on that kind of floor.

 

[kbs2244]

The more joists or rafters you span the greater racking strength you have.

 

[Rockey]

In case your wondering if this is really important.....it is.....please don't ask how I know....

I have to ask because I didn't stagger mine. I'm guessing the inspectoris going to make me tear it up?

 

[blkhonda1991]

I have to ask because I didn't stagger mine. I'm guessing the inspectoris going to make me tear it up?

ouch...thats going to be a tough lesson to learn if so, even if he doesnt make you tear it up, i certainly would redo it

 

[KMR Construction]

If you run advanch with the floor joist it will come up short. It measures 47 1/2", 48" to the outside of the tounge

 

[nate379]

I don't know what you mean by parallel or whatever.

If the floor joists are going west east, then the 8ft long part goes north south. That is how I have always done it anyhow.

 

[archirelic]

It is what one of my instructors calls a 'cross-stitching' effect. The overall ability to resist loads is greater when the subflooring is 'cross-stitched' against the joists.

 

[southernfriedcj]

I’m using Advantech sub flooring, I’ll look to see if it has strength axis marked on it. What should I be looking for to indicate the strength axis?

http://www.advantechperforms.com/dare-to-compare/product-testing.aspx

Advantech is great stuff! Yoiu might also want to check out Edgegold. It is just as good in my experience and you can save $2-$3 dollars per sheet.