Granite countertop installation on top of 4x4 outdoor

Question

I am planning to have a piece of granite countertop 2' x 8' outdoor like the below photo.

I could run two (2) 2x4 on the side of the 4x4 posts to make the bottom materials 7" wide. Then lay the outdoor plywood (black color ones) on top. The granite will be on top of the plywood.

(photo doesn't show the plywood)

My questions:

1. Is this "setup" strong enough to support? The 4x4 are mounted on top of deck beam and joists. So those are OK. I am wondering if I need to do three rows of two 2x4 each (total of six 4x4) instead of using three 4x4.

2. Is there regulation / best practice on the two 4x4 on the side in term of how far from the granite edge? I am thinking about 3" from the edge. That leaves me 1.5" plywood overhang. And then another ~1.5" for the countertop bevel edges. So basically, I should try to get the 4x4 as close to the side edges as possible, right?

Thanks.

Answer 1

1). The answer is really time. Nothing lasts forever. The more activity it sees the shorter the lifespan will be. Obviously, supporting the edges would make it more robust.

Your design may last many years, but I would be tempted to use angle brackets or cross members on the ends to prevent wobble, or perhaps use four legs (one in each corner) but that may be a matter of function vs. style. Otherwise, there are a vast array of angle brackets which would be suitable for this. Some factors to consider are whether or not you want the brackets to be ornate or hidden; material considerations (wood, wrought iron or even cable possibly); and of course, budget.

2). There may be regulations (safety tests) for commercial chairs (depending on what the retailer wants)... or if you build this for someone else, as part of a contract, you might need to stipulate repairs and liability in the contract.

As for three-leg-placement options, I think that the golden ratio is generally good. As such, I would center the outer posts at 2.472 feet (approximately 2', 5-11/16") on either side of the center post. Of course other arrangements will also work.