LVL or 2 layers of plywood for stair treads

[Vipul Acharya]

I want to build a stair case and clad the treads, so the appearance of the tread is not important. I am wondering whether to use 2 layers of 1" plywood or 1.75" LVL laid flat. I can't find the modulus of elaasticity for the LVL about the weak axis. The stair treads are 48" wide x 12".

Thanks!

 

[milkshakelake]

I'd go for the LVL. The two layers of plywood wouldn't act compositely, meaning you have a much lower moment of inertia, which would result in vibrations/deflection. You could stick them together with nails to have them work together compositely, but then you'd have nails sticking out and it's extra labor.

 

[BridgeSmith]

I agree with milkshakelake about the LVL being stiffer. However, I don't think nailing the plywood layers together will provide substantial composite action, particularly with regard to stiffness. To get the stiffness of a composite section of the 2 layers of plywood, you'd need to glue the layers together with a rigid adhesive, such as PVA wood glue.

 

[Vipul Acharya]

Yes - I was thinking about screwing and glueing the 2 layers of plywood. 1.5" - 1.75" screws, both ways would make it stiff. I'm just curious if anyone has the E for LVL (lowest grade) about the weak axis. Is it different from the published value about the strong axis.?

 

[driftLimiter]

Have your Reviewed Weyerhauser document TJ-9000?

There is guidance on determining deflections, Section and material properties, and there is some info about 'plank' orientation.

 

[Vipul Acharya]

No I was not aware - I just looked it up. Thank you. I am surprised that there is no difference in youngs modulus in the plank direction...interesting. I would have thought that they manufacture and orient the strands so that strong axis is stiffer than weak axis.

 

[Vipul Acharya]

So comparing 2" plywood (assuming it is properly glued and screwed) to LVL (1.75")
Plywood - E = 8GPa
LVL 2.0E = E = 13.8 GPa

Tread is 12" wide

EI plywood - 8 x 305 x 50 x 50 x 50 / 12 = 25.4 .......

EI LVL - 13.8 x 305 x 44.5 x 44.5 x 44.5 / 12 = 30.1.......

LVL is stiffer.

 

[kissymoose]

Depends how far apart the stringers are, it could not matter.