Plywood - stiffest configuration?

[Darro]

Can anyone tell me which of two plywood sheet configurations would be the stiffest, or do they have the same stiffness?

Any other observations about the stiffest configuration of plywood sheets under 5/8" thickness?

Configuration 1: A bottom layer of sheets of 1/4" plywood plus a top layer of 1/4" plywood sheets overlaid in the centre of the lower layer's joints and glued to the lower layer.

Configuration 2: A single layer of 1/2" plywood with the same outside dimensions as Assembly 1.

Thanks in advance for your helpful replies.

Darro

[Edwin Pawlowski]

In configuration 1 you mention joints.Are you laying out a series of sheets and then staggering the second layer? Done properly, that would have marginally more stiffness at the joints. Lots more labor and no assurance the glue joint is as good as the factory ply. I'd go with the single layer.

[Wayne Whitney]

Assuming you are doing a large area with multiple sheets, how about

5/8" T&G CDX plywood?

Cheers, Wayne

[G Henslee]

For what application?

[bigcat]

not enough info.

fwiw a wood frame sandwiched between the 2 would give even more stiffness in some ways, less in some.

NT

[Josh]

"Darro" wrote

The local lumber yards here, sell 1/2" CDX with 3,4, & 5 ply. Five ply will be your stiffest (and most expensive out of the 3 choices) plywood, the plys are alternated when glued/compressed together.

IMHO, stay away from 3 ply for any application except when hung vertically for exterior walls.

[Joseph Meehan]

All else being equal a single sheet composed of the same total number of layers as two sheets half as thick and having half the total layers as the single will be stiffer. However that difference is not likely as the total number of layers will not likely be equal and you need to consider the overlap of joints that will add overall application stiffness. In addition there are many other factors relating to stiffness.

[ConcreteFinishing&StuccoGuy]

Iff stiffness is the only consideration and water resistance is not a factor, then wafer board offers greater stiffness than plywood, not overall strength, just stiffness.

-- Troweller^nospam^@canada.com

[calhoun]

4 ply? that would be strange, grain would run different front to back. Guess it would make no dif if installed across the joists or parallel to them. Don't see much straight dif from 3 ply.

[Josh]

"calhoun" wrote

Being _normal_ building grade sheets are 4'x8', it sure does make a difference how it is installed.

Guess if you've never used the better grade of 4 ply compared to 3 ply, you wouldn't see any difference.

[BobK207]

In 4 ply, the two center plys both run the same direction.

Go figure.

Bob