Here's a great thread for you. According to the thread's author, 10" is the max unsupported overhang you can have with granite. I'd make the fabricator come back and do it right!

Here is a link that might be useful: Stone checklist

The biggest problem that I forsee with throwing it on to the shoulders of the stone fabricator is that the cabinets themselves have to be designed from day one to have the internal support to be able to support the granite. You have to have some sturdy attachment support for the corbels or brackets. Or, your GC or granite fabricator has to be one that offers steel support bars under the granite. This has be be at the door of the GC to solve, as it's a multi trades task.

I guess the installer stretched the limits. Happens all the time. I have seen bigger unsupported. The homeowner loved it, "Nobody is going to sit or stand on the counter" is how she justified having it like that.

Talk to the guy. The visible gaps concern me more.

David

You could install some corbels under it to support it. I would not leave it unsupported. I have grandkids and you know how they can be! I can just picture a kid climbing up there for something and the granite snapping off.

Corbels will only work if the island back is more than just cabinets w/decorative doors....I seem to recall you also need a 3/4" wood panel for support...I know something like that was done to the back of my peninsula to support the corbels.... We have a 15" overhang.

Perhaps Kevin, Joshua, Mimi, Paulines, or other stone guru will chime in. I think Live_Wire_Oak mentioned this on a different thread a month or so ago.... (Hence her comment "...the cabinets themselves have to be designed from day one to have the internal support to be able to support the granite...")

We don't have supports on our granite overhang and have never had a problem. 2 houses ago, we had a 12 inch overhang that was about 8 feet long. This house and the last house had an arched overhang that was 10 inches on both ends and 15 inches in the middle. It was 8 feet long in the last house and about 6.5 feet in this house. Since the granite is 1.25 inch granite, all three times, we were told that a support wouldn't be necessary. Honestly, we've never had a problem, and our counters have taken a lot of abuse. Our kids like to stand and sit on the island, and It's not been a problem. I don't know, may be over time it will weaken, but so far so good.

How wide (or deep) is your countertop in total? I'm being a bit extreme in my example but if you have a 2 foot wide counter and 11.5 inches of that was unsupported then you'd have the countertop tipping over very easily. However, if your coutertop is 4 feet wide (or deep) and 11.5 inches of that is unsupported then the weight of the supported side is more than adequate to keep that countertop from tipping towards the unsupported side. We have a 3 foot wide counter that is 6 feet long and 10.5 inches of that is unsupported and I can sit (105 lbs) on the unsupported side and it doesn't budge!

But, you also didn't indicate what your concern is...are you concerned with it tipping or with your cabinets not being able to handle the overall weight? I'm assuming the tipping issue, but didn't know.

Also, they should have put a bead of silicone or something to seal the coutnertop to the top of the cabinets.

HTH...

Ordinarily, unless it were a part of the specification and agreed upon at the time the stone was ordered, it's not up to the stone fabricator to come up with supports for the slab. Any supports would be a part of the cabinetry. The stone fabricator simply provides the stone in the specified size, thickness, and finish.

If your stone fabricator didn't agree to supply a support system, I don't think you can go back to him at this point, unless you're willing to pay for any extra after-the-fact work.

That being said, if the fabricator thought there might be a problem with an unsupported overhang, it would have been nice of him or her to mention it at the time the stone was templated. It's entirely possible that in your fabricator's opinion, an 11-1/2" overhang is nothing to worry about.

Was a kitchen designer involved in your project? If so, that's the person to whom you should be talking.

Another option, we have 4" square legs that go to the floor supporting our overhang.

Thanks for all the comments and advice. I'm just sitting here the last couple days not really knowing what to do. Our GC isn't worried about it. He has a friend who is a fabricator whom he called for advice and he wasn't worried about it. Our plumber also works for a granite company and said their guideline is 12" for adding supports to an overhang. Of course, I called the installer and they also said they use supports for 12" and over. All this makes me feel somewhat better, yet after reading other comments there is a part of me that can see myself constantly watching over the kids over the years as they go to lean on it when doing their homework, eating, or simply hanging out. Ugh! Thanks again for the feedback. We are not quite sure what to do, but are definitely sending the installer a letter.

I agree that 12" is the max without support
If you really feel uncomfortable price supports with your cabinet company to match cabs. or maybe you could add matching legs
Sometimes the granite fabricator can put thin steel supports in under the top, but I don't think it's necessary
It's highly unlikely that it would ever tip over so don't worry about that....