Quick easy subfloor question

[Nate R]

I have some 3/4 T&G Subflooring that I will be putting down soon. Is there a preferred direction to face it in relation to the joists? Across the joists or with them?

[jadnashua]

Absolutely...if you want the stated strength, the grain of the top layer of the ply MUST cross the joists at 90-degrees. It also helps if you use construction adhesive on the joists.

[leejosepho]

Yes, you definitely do want the T&G edges to span from one joist to the next. Otherwise, the merely-butted ends of sheets could move against each other.

[frenchie]

Also the lay-up of the layers, in the plywood, provides more fibers going the long way, than the short way. If you laid it with the long side parallell to the joists, each sheet would be weaker / less stiff than running it across.

[leejosepho]

I have some 3/4 T&G Subflooring ...

Is plywood being assumed?! This could be OSB ... ;)

[Bob NH]

OSB is stronger in the long dimension and should be installed like plywood is installed. Plywod and OSB are about 1/3 as strong in bending in the transverse direction as in the longitudinal direction.

OSB flooring (5/8"; 15.5 mm) is about 40% as strong as Douglas Fir Plywood and about 60% as strong as Canadian Softwood Plywood in the strong directions. See link below.
http://www.canply.org/english/products/comparison/comparison155.htm

[Nate R]

It is OSB, I should've specified. Thanks for the answers!

[frenchie]

OSB or ply, no difference - more strands on the long axis, in both cases. That's why it's called Oriented Strand Board.