New Shed - floor weight capacity question

[kingofbytes]

Hi!

I am purchasing a Post Woodworking shed 12'x20'. I'm upgrading a few things, specifically the floor, to be able to store a car in the winter. Pouring a concrete foundation isn't an option at this point.

The shed floor will be built with:

1. 12" OC 2x6 PT Floor Joist
2. Joist hangers
3. Double 5/8" Exterior Grade Plywood Floor (stacked on top of each other)

I'm wondering what the maximum weight this floor could handle? Thoughts?

Thanks!

[KennyG]

From an old beam table I have, a 12 foot span 2x6 will support 420 lbs (distributed load) at a Fiber stress of 1000 psi, which should be a reasonable value for pressure treated. With 21 joists, that would give you a total distributed capacity of 8820 lbs (neglecting any contribution from the plywood other than distributing the load). Given the point loads of the tires of a car and the need to consider some live load, I think you may be a little marginal on the design. I don't think it would be safe with less than 2x8 joists and, if I was doing it, I would go to 2x10 or 2x12. The cost won't be that much higher.

[kingofbytes]

Thanks KennyG, that helps. If I have a choice, I'll see if I can upgrade. I'd love to see how 1.25" of plywood stacked changes the distribution/load on the 2x6 though.

Again, thanks for checking!