Supporting a Granite Countertop Overhang

Under a thin granite slab top, a plywood subtop is needed — for support and to attach legs. August 7, 2006

We have a kitchen cabinet job with a peninsula and a 3/4" granite slab overhang of 12". The design calls for freestanding legs to support the overhang. The top of the legs will be about 3" inward from the outside edge. The legs are 34-1/2" in height with a 2" round surface contact point on the floor and a 3"x3" square top.

I'm aware that I can use a sure-tite bolt for the bottom. However, what is the best way to secure the top to the granite? The slab is only 3/4" thick. I was thinking about using a strip of steel flat bar 1/8 x 1-1/2 x 6 and attaching with screws to the top of the post. I would then ask the granite fabricator to dado out a channel roughly equivalent to the size of the flat bar so I could epoxy the wings of the flat bar inside the dado channel. Any ideas would be appreciated.

Forum Responses
(Cabinet and Millwork Installation Forum)
From contributor A:
Our granite supplier tells us that any overhang more than 10" needs full support. We solve this problem by calling for a 3/4" full finished plywood pad that cantilevers the cabinets. This gives you all the support you need, plus something to attach the legs to. Inset the pad to match the countertop overhang with the rest of the cabinets, and they won't even know it is there. Without a pad or apron tying the legs to the cabinets it will look like something is missing.

From contributor B:
The plywood subtop is the best way. Screw the leg thru the plywood and put a rail bolt in the floor. The subtop will also give a more even flat surface for the slab to sit on, then there is less chance of getting uneven pressure potentially cracking the slab.

From contributor C:
The plywood sub-top is the way to go. Whatever you use, make sure your legs and base are installed completely before the granite goes on. If the granite company places their top on your base, and down the road it cracks, you will be in a stronger position as far as liability. I would make the owners sign off on the fact that 3/4" is too thin for overhanging granite. 1-1/4" thick is the minimum for overhangs. Make sure you are not held liable if that thing breaks.

From contributor D:
I concur on the apron method. A 3/4" piece of granite is one thing and one thing only -cheap. I would try to incorporate a 3/4" profiled solid apron that matches your cabinet style. If I had to deal with 3/4" stone I would put a cove under it anyway (on the face frame). My upper FF rails are 2" so I would think that would provide a place to hide some more support and provide some attachment for your legs. Do not use adhesive to attach the legs - it will bleed to the top of the stone.

From contributor E:
I would not consider a piece of floating granite with no sub top. This is a bad idea and whatever happens will be your fault. Whoever thought that they could cant a piece of granite without a sub top is misinformed - don't add yourself to this misinformation.

From contributor F:
The dilemma we have is that the current subtop, for all the cabinets, sits inside the base and is flush with the top of cabinets. With 3/4 slab and edging and a nominal 1.5" overhang you have to seat the subtop flush or else you'll be looking at plywood ends.
Hence, a cantilever subtop for the peninsula base is problematic. Given this limitation is there another option I could pursue?

From contributor G:
We just recently had the same problem. We took two pieces of 3/4" MDF and glued together and edged banded the edges of the same wood the cabinets were made of. It made for a very solid top.

From contributor H:
I might see doing this with 1-1/4 but ¾ equals definite breakage. You need a sub top. Cut 3/4 off legs, screw top down to legs and screw top into side of cabinets from either the inside with regular screwing methods or, if there is no room, use pocket screws from the underside of subtop into face of cabinetry.

From contributor I:
Yes, I think the stone top fabricator should provide a self edge on the stone tops to conceal the necessary plywood sub tops. Why should the burden fall completely on you?

From contributor J:
I have installed a couple hundred kitchens in the last two years, most of them receiving granite tops. Out here in Vegas all the granite companies use ¾ (1-1/2 in the midwest) Standard protocol is a 5/8 sub-deck and I have never seen one go in without a deck on the top of the boxes. This allows for the edge treatment which would otherwise come down over the face frame (wouldn’t work with full overlay). Perhaps this granite has no edge treatment beyond 3/4. I do think your idea with the steel is a valid solution. You could change your 6" number to 18 or 24, allowing you to tie into the cabinet. As somebody else suggested you could put a subdeck on and trim it out with a cove, or scribe that matches the boxes.