I need help on supporting a 12" countertop overhang.

My kitchen island is two sock 24 x 36 cabinets butted up together.
They are typical builder particle board Lowes / Home Depot grade of cabinets.

So the island length is 72" and width 24"
On two adjacent sides there will be a 12" overhang.
So the granite will be 84" by 36" with 3” radius corners.
Picture a rectangle with a bigger rectangle hanging over it.
The granite is 22/sq ft x 7’ x 3’ = 462 lbs.

I am getting 3 cm Black uba tuba granite. No lip on the granite. My granite company says I am fine but can't guarentee it without support.

I have done some exhaustive analysis and here is what I came up with.
3 cm granite does not need sub-counter (3/4” plywood)

1) I can get a 81" by 33" Steel sheet. Don't know if I need 3/8” or ¼”. I am concerned about the weight and appearance (no lip on granite). If I go with this which thickness do I need and how much will this weigh?

2) Korbels or metal angles. Should be 6” from end, then 40”, 72” on length.

a) Korbels are big and expensive. The will be knee knockers. How to hang from cabinet.

b) 8 “ metal angle. I can use some sort of oak char rail and route out the back. Cover 8 “ metal. Do I need a boad or do I have granite sit on the metal? A ¾” board would be ugly.

c) metal shelf bracket. Celtic knot shown in picture.

3) I have seen people use steel bars and route them in across the top. I have not found any steel bars.

I did find a stock steel shelf rail. The kind with slits in it that you wold put shelf hangers and then shelfs. The rails are about ½” wide and deep and solid on 3 sideds, It can be purchased 6 feet for about $5.

I would put the U with the flat side up. And cut half inch slits in the top of the cabinets so they would lay plush. I would cut them 32” (4" short of the overhang) and lay at at 3”, 18”, 36”, 54”, and 72”. The rails would extend 8" along the long side.

Not sure what to do on short 3' width side. Could probably rig the same rails or on go with a 9” overhang on that side.

I am leaning towards the black shelf rail functioning as a bar.

Hope you can picture this. Can I attach a picture?

 

Typically, there is no problem with the standard overhang. Some take extra precautions by installing a piece of sheet metal to support the island top. Others fashion a variety of support systems. Corbels make for great overhang support. They come in a variety of sizes and styles to complement your cabinetry. They do not have to be 'knee blockers.' Some make their own corbels.

 

Let the installers/fabricators make the decision on what needs to be done to that overhang. You'll want them to warranty it - yes?

 

Here is what I came up with.

I glued plywood to inside of cabinets with construction adhesive.
I also use 1 inch lag bolts to get it tight. 3/4" plywood + 1/2 particle board.
Be very careful drilling hole for lagbolt. I used blue painters tape to mark off 1 inch on drill bit. Just wrap it around bit.

I then put 10" steel brackets on inside of cabinet.

NExt to drawer was trickiier. I used 3/8 inch plywood, glue on twice and then had to recess bracket so I would interfere with the drawer. I also had to cut the bracket short.

The sales guy said brackets were not necessary. The installer said they were.

The island looks great and you can not see the brackets.

http://img02.picoodle.com/img/img02/7/2/10/ncdad/f_Bracketsm_81d38a3.jpg