My island (8 feet long with overhang of 6 to 13 inches, curved) is supported with three steel flat pieces that run the depth of the island. The plywood was routed to hold them on the underside. It doesn't look pretty from beneath, but unless you're cleaning the floor you don't see it. My cabinet guy didn't think it necessary, but my marble fabricator said yes.

Here's a link to another thread that may be helpful. If you scroll down you can see some photos of supports that some people use that you can't see unless you look underneath.

Here is a link that might be useful: Overhang thread

Thank you everyone!

ca mom, so do you have the piece of plywood cut JUST the right shape as your stone? If then did you get the exact template from the stone person for a carpenter/cabinet person to do it for you?

I don't think I will mind having a layer of plywood. It's just finding out how to exactly cut the plywood and having the steel embedded.... an yu tell me how wide and thick the steel pieces are? THank you again!

Not the best solution; but, assuming you are using 3cm granite, cut the overhang back from 12" to 10" This is about the maximum you can cantilever without any underlying support.

This is what we did. Its a bit tight, but we have no problems sitting and eating at the counter, and our knees don't hit the cabinets.

Both our cab and soapstone guys said we would be fine going without a support with a 12 inch over hang.

I think it can vary with the type of stone. Some is more fragile.

The plywood is put on before templating and cut to be flush with the cabinets on the side without seating overhang and extending about an inch or two less than you want the overhang on the overhang sides. The templater than measures the plywood and the granite top is made to fit. At least that is how it was done for us.

Our steel bars are about 2" wide and 1/2" thick.

The steel bars can't crisscross. There isn't enough thickness of the plywood for that. To support an overhang on two sides, the steel bars could run at angles so that they radiate from the corner opposite the overhangs. Our bars were angled to avoid the prep sink and range top cut outs. Our bars are long enough to run all across the top of the island.

Our granite has a laminated edge that hides the edge of the plywood. I have friends who don't have a laminated edge who used a piece of molding stained to match their cabinets to cover the plywood edge. The bottom of our plywood is unfinished. I wish I had thought to ask our GC to use one with cherry veneer facing down and stained to match our cabinets. Nobody but me notices it.

I talked to my templator and he said something along the line of "we did not tell you about the support since we did not see those plastic legs the island is standing on." ?! I thought the overhang support was for the stone not to bend/crack along the overhang area, not to prevent my island from topling over! If that's the issue, we have to get better legs for these IKEA cabinet and anchor those legs down.

I talked to one of the steel fabricators in town and he can help me to get some steel plates 1/2" thick and 2" wide. I just have to figure out how to anchor these onto the cabinet...

Oh, thank you, cloud swift for your information. We must have been writing at the same time! How thick is your plywood? how spaced are these bars?

Glad I read this thread. It reminded me that we are supposed to have 3 steel supports @ our granite overhang (sorry I don't know the overhang dimensions). I did not see any supports underneath so I just called my GC to check on it.

check out these overhang supports on wholesalehiddenbraces.com, just did a quick search...

Here is a link that might be useful: hidden brace