Yes, preferably either a steel strecher bar system or at the very least the Federal brackets. No way around it safely.

What is the thickness of the granite. Rods can be set in grooves to reinforce it; ask the fabricator. There are numerous hidden brackets available.

3 cm (about 1 3/16") will cantilever 12". 2 cm would not.

A 12' Long Island is going to require muliple pieces of counter material, with a seam. You may want to rethink that. The NKBA recommends a 15" overhang for a seating at 36"H counter, not 12".

Yes, insist on the brackets. Would you like to take a chance on the stone cracking and/or crashing down on the overhang end because it’s not properly supported? Buy the brackets yourself and install yourself if you have to. We have the ones RES posted and they are awesome (ordered direct from their site though, not via amazon) and the company was great to work with when I had questions. While you’re insisting on things, also listen to GreenDesigns and increase the overhang to the NKBA minimum of 15”. 12” is too shallow and it’s not comfortable for anything exceeding a quick snack or drink. If you don’t want to be banging knees on corbels then you probably don’t want knees and shoes banging on the back of your island cabinetry. You wouldn't think 3" makes that much of a difference, but it truly does. Don't build a huge 12 foot island and skimp on the overhang.

"National builders" are typically selling a finished home to their specifications, plus some extras. If it isn't offered as an option, don't expect to get it.

Can you replace with corbels with L-shaped steel (steel L shaped corbels). Maybe. Its important to have good attachment points on the cabinet in order to transfer the load. Once you modify, you take on the responsibility if the slab cracks, etc.

Corbels have to be attached to something more robust than a 1/8" cabinet back. The whole support is only as strong as its weakest point. The whole has to be designed, from the beginning, to work with the support chosen.

If the brackets are put in BEFORE the granite, it is a easier to put in the needed support on the inside back wall....why would you do it after? They will be almost invisible if done before especially if you paint them to match the underside of the granite. Corbels with no added cab reinforcement is not really helpful.

What is your guy’s issue...I do not get why you are getting pushback on this! Pay him extra if you have to.

An 18" overhang needs at least 36" of cabinets to anchor a cantilever properly and meet the required 2/3 to 1/3 cantilever ratio. In addition to steel. Better would be table legs and stretcher bars that create an attached table. If you want to cantilever, stick with the 15".

Countertop fabricators often sell support brackets. Whoever is installing countertop should be able to assist with this.

Well done!!! I have 15” with metal supports, no legs or stretcher bar...15” works well, but we have a nearby table. The island is not our only seating.

Most stone slabs run around 60" in depth. Which would limit your overhang to 10" by the time you account for the overhang at the front. You might be able to find a 65", but you lose an inch or so all around. Slab widths are around 108".

You're asking for something beyond Jumbo size in both width and length. You are already going to need 2 bookmatched slabs, just due the oversized length. If you don't get the depth under control, and within the real world size limitations of stone slabs, you are going to need 4 bookmatched slabs, just for the island. No one wants a 20K stone bill just for the island.

You need to reduce the depth of the cabinets on the island if you want a significant overhang. As in take off the cabinets on the back. Then 2 bookmatched slabs can have the seam in the middle, front to back. Or remove cabinets to reduce the width, to fit within one slab length that way. Then 2 slabs can have the seam horizontal instead of vertical, and you can have the extra deep island.

You will need an excellent stone fabricator to make any of this work. This all takes above average skills, which come st a price.

Post the actual layout, with all of the cabinets, and the cabinets specs of how they are built. The island isn't created in a vacuum and then plopped in with a crane. It has to fit in the space with adequate traffic paths on all sides. Plus, it has to be structurally strong enough.

Any added support needs to be every 18" and come within 6" of the edge. The cabinets themselves will need to be more robustly built and reinforced so accept large brackets that will resist so much weight from leverage. The cabinets will also need to be securely fastened to the subfloor.

Legs with stretcher bars are always the better choice. Large cantilevers, floating in midair, are not a good design look.

Rather than corbels you could add cabinets with open shelving or glass doors on the ends for additional support. Could be a very pretty accent. Our island is just a smidge under 12' but we only have two seats - one on the short end and one on the long side but have an 18" overhang. DH is 6'5" and it works better than the 15" we had in the old kitchen.

If your kitchen is a modern design, you could use exposed metal brackets instead of wood. The apron under the overhang helps to hide the metal supports.

wildon853, you do have additional steel under that, right?

Side panels do nothing real. You need steel.

Newfie, I have a narrow island with only two seats. The drawer base in the foreground is shallower at 21" deep to give us more legroom behind it. There is 22" to the right with the countertop. A deeper overhang will give you more choices in stool depth which is important for a taller family.

An update: Thanks to your advices, I did have a meeting with the PM, and was able to ensure there was enough support. The final size of the island is 13’ x 5 1/2’. We now have an 18” overhang, proper support, and hopefully, we will close in a few more months. The island looks like this now.

Question. How high are the pendants from the counter? In the photo they look too hight but that could be the photography.

Glad to see you have proper support and that stone looks gorgeous.

It's really hard to tell from photos. You'd have to be able to see the entire room from different angles to really know. I have on occasion raised pendants noticeably higher than what standard guide lines say, and the results were much better for all the sightlines.

Fortunately, I had a really good electrician who took the time to let me try out different configurations.

That's why I said it might just be the photos.

Like you mine were hung a bit higher than guidelines because hanging them lower with our 10' ceilings just made them look too low.

Newfie:

What specifically supports your 18" cantilever, please?

That is one pretty island! :-)

Glad that you were able to get all of that worked out. Those kinds of things can be so stressful. I imagine big parties with lots of food around that beautiful island!