I often use 3/4" baltic birch plywood under the granite with a double thick granite perimeter edging. There are many metal brackets made for this purpose too (see link).

Here is a link that might be useful: counter supports

Not so sure that we would like the look of a 6cm edge.

I've seen the flat brackets, but there is no pony wall to secure them to.

We could use two of their "islandbar" brackets, but what to do about having a center bracket? The cooktop will be in the way of mounting one.

Stretcher bars and table legs in the middle will work.

But personally, I'd prefer to actually face the seated people and not splatter them with burning grease. 70% of your kitchen tasks are prep related, not cooking related. Only 10% is spent cooking. 13 1/2 inches also isn't enough safety clearance behind a cooking zone to have seating there.

I am interested in this topic too! bump

Since you will have a cabinet there, even if a cooktop will be on top of it, your carpenter can reinforce the back wall of the base cabinet so that you do have a "stud" to attach a brace to. That is what we did with my island overhang. My braces are from Federal Brace. Under the pictures of my island braces, I linked below to one of the four "hidden braces" they offer.

Since you will have a base cabinet on the right and left of this 5 ft knee-hole opening, though, can you not put steel reinforcements between the right and left hand cabinets? You would just need to trim down the sides of the two base cabs for the width and depth of the flat steel supports. What, a quarter of an inch deep and two inches across at most? I would make sure the supports spanned both sides of the base cabinets on both ends, fitting snuggly across the top of the right cab, the empty space, then the left cab. Make it a 2" wide flat steel piece, situated six inches out past the cooktop cabinet, laying in the right-to-left direction. Do another support bar another five inches out. The steel supports will be flush with the top edge of the cabinet sides. That means the stone will be supported at 6" for 2" and at 11" for 2". The steel is only a quarter inch thick, a simple decorative edge will hide it from anyone looking at the kneehole from a distance. Since the support steel is inset in the top edge of the cabinets, and the weight of stone is holding it in place, it is not going to move. You will have a quarter-inch of steel coming down into the top of your drawers in the left and right cabinet drawers. I doubt you can even see it. Shouldn't that provide enough support for the 5 ft opening that is just under 14 inches deep?

Here is a link that might be useful: Federal Brace Hidden Braces.

Why would you assume a thickness of 6cm (2 3/8"). I was describing a 1 1/2" counter which is standard in the US.

This is a common design issue that should be easily solved with standard hardware without knee-knocker brackets. A drawing might make it possible for others to help.

Here's a drawing of the island, with and without the counter top, if that helps visualize the issue.

@hollysprings - The seating will only be used occasionally. More likely while prepping for a holiday meal than while actualy cooking.

@nancy_in_mich - I'm the carpenter for this project;-) I'll have to get the drawings for that cabinet from our cabinet maker, so I can see what type of space I will have along the back wall of the cabinet for any bracing to be added. There, of course, needs to be room for the cooktop to drop in, but also for the drawers to close all of the way.

Metal is far better than wood.

Wood flexes under load far more than stone.
Grooves in the underside of stone do not have to be wide so much as deep.
Even steel only 1/8 in thick and 3/8 high is surprisingly strong if you try to bend the 3/8 dimension, especially if it is in a groove filled with epoxy.

You need steel.

But, you also need to reconsider the cooking zone on the island. The space beside the cooking zone isn't large enough for a comfortable prep zone, and you will end up with your back to anyone seated because of that. Plus, I agree that it's a safety hazard with that minimal amount of overhang behind the hot stuff.

@GreenDesigns - To me, it seems like a good amount of prep space on the left end of the island. As for a safety hazard, this is not intended to be a breakfast bar. It will likely only be used on rare occasions, like holidays. We certainly aren't going to have our guests sit there if we have grease or other hot liquids splashing around the cooktop;-)

Anyways, I think that we will just hide a stud wall inside of the island, so we have something to mount the hidden brackets to. Our cabinet maker can make the one back cabinet a bit deeper to compensate for the depth of the wall.

Forgot to post the new drawing.

I am not crazy about your knee-wall idea. Then you really have no place to put your legs when you try to sit in that space. Why not just run steel supports parallel to your planned stud wall and cut out the edges of the cab boxes so that the steel supports are flush with the top of the cabinet sides? They will be practically invisible and no one is going to bang a knee on them.

As for space, see the top of my island, below. Ours is an induction cooktop, so a lot less heat is involved. We also tend to boil, saute' and pan fry, not high-spatter methods of cooking. Measuring from the back edge of the cooktop (there is a black downdraft behind it that I am including in my distance), we have 19" to the edge of the island where our guests sit when we gather to cook. My sister-in-law always suggests that we have a family brunch at our house when we get together, so we have five or six adults around the island cooking, chopping veggies and sipping mimosas. We all enjoy it. So I have to say that 19" is sufficient for an induction cooktop. I wonder if folks will be sitting at yours when others are cooking, with a much narrower overhang. Oh well, it still makes a good place for the cook to sit and chop veggies!

On each side of my cooktop there is about 18" close in, but the island quickly widens and within reach of the cooktop, you get 29" of prep space on each side. On your drawings, you have at least 30, since you have a 30" cabinet to the right. You probably will have an inch or more of the cooktop cabinet that is not under the actual cooktop, plus an inch overhang at the edge. You will have 31" to 34" and should do fine with that amount. It looks like you have a similar space on the other side. I agree that your prep space looks plentiful.

@nancy_in_mich - That ends up being the same overhang depth as the original drawing. We just pushed some cabinets forward to fit in the stud wall. On your island, what is the actual overhang?

It is certainly not ideal for sitting, but as I mentioned before, it is not expected to be routinely used for that purpose. We expect that space to be used more while entertaining, for setting out food and drinks.

We could have filled that space with cabinets and not had an overhang. Though, that would have added to the cost of the project and we already end up with a ton more cabinet space in the new kitchen design.

This post was edited by gpraceman on Tue, Apr 9, 13 at 12:31

Iron L bracket that secured on the back side with notches out to stay level would prolly work??

I’m using The original bracket Company to try to do a 32 inch ( at the longest part bistro ish bar over hang.

they do custom stuff, so we’ll see if we can have it floating! Lol

"I’m using The original bracket Company to try to do a 32 inch ( at the longest part bistro ish bar over hang."

Bad idea. You need a custom made frame.