Granite Gurus - how would you support this much overhang?

ni_2006

15 years ago

We will have an island that is about 72 inch x 60 inches with a column going through the island on one side. We will have quite a bit of unsupported overhang, which I am worried about. I am not crazy about having corbels since they will be in the way, but if that is the only way this would work, I am OK with that. What is the best way to support this without using corbels? Please help!!!

Here is a link that might be useful:

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Comments (13)

malhgold
15 years ago
what about some sort of round pedestal in the middle that won't interfere with the seating? I'm assuming you're putting stool there.
zinnah
15 years ago
That is quite a bit of unsupported stone. Think metal, possibly a 2x2 square tube run corner to corner, possibly another one or two inboard from the outside, less obtrusive than corbels.
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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.
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Need advice please. have island 10ft long island x 4ft 2" (50inches)wide. overhang will be 12 inches down the entire 10ft length. have 24"d base cabinets plus another 12"d set of base cabinets back to back. (36 inches of base cabinets that granite will sit on). question is how many support posts will be needed down the 10ft length of overhang ?(14inch overhang) Will one support post on each end be sufficient or do I need 3? can't add metal supports into top of cabinets, not enough space between the cabinet doors and top of cabinets. no room for corbels. support posts are the only option. would like one on each end vs adding one in middle. help!
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Thanks for your responses. Mindimoo, your steel structure is awesome. No worry there. I wish I had researched this much better before having my kitchen demoed and ordering the granite. You both have some good points and good questions. My granite is 3 cm. It is black (Labrador Angola) which I am told is the strongest of all granite because it is much less porous than the lighter colors. The steel rods are threaded and they are imbedded in the bottom of the granite, covered by epoxy. So, water isn't an issue. There are 5 rods total. I don't know what it's called or what size it is. Looked like 1/4 to 1/2 inch. They say it's made for granite and the concept is similiar to what is done with concrete. One rod is in front of the cooktop cutout. One on either side of the cooktop extending to the 13" overhang, and two on a diagonal to each corner on the other end of the island which is where the 15" overhang is. These two probably don't meet the 2/3 to 1/3 rule. My original plan was to do something similar to the picture above in plywood. When I contacted my Lowe's cabinet installer to say I wanted to go back to Plan A he said it was overkill. He says he has demoed numerous kitchens where they had used the steel threaded rod and it is really difficult to break the granite. He was confident in their approach. I like and trust this guy but he is super busy so I hope he wasn't just telling me this because he didn't have time to help me prior to the install. Anyway, the granite was installed today. The fabricator gave me a written warranty that it won't crack as long as we don't sit or stand on it. I still have mixed feelings about the support. I still have the option of putting corbels on the end of the island although I wanted to avoid them because they are tough on the knees. But then again I wanted 15" there for the extra leg room since that is what many seemed to recommend on this forum. Also I could have L brackets on this end. There are doors on both sides of the island but the ends will just have panels (fake doors) which can be cut or notched for corbels or L brackets. I'm thrilled that the granite is finally in. I've been 2 1/2 months without a sink. I don't want to regret not researching this more than I did or rushing into things. If only I knew about this forum sooner. The feedback has really been great! Please let me know what you think. Thanks again!
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I review the plans of everyone working on my house. [...] My general contractor and the granite fabricator/installer will warrant their work, and like everything else going into my house, I want to double check, and I want them to justify their plans if they differ from what I have learned from Professor Google. We don't have their plans though, if that sketch was given to you as their plan for support, then you are in trouble and need to hire another professional. To evaluate their plan we need to know what system they plan to use to limit flex. Make a wall beyond the cabinets, or close in the ends. for additional support. I am not a huge fan of walls that dissect long pieces of granite unless the people building the walls really understand what they are doing. I think the post is a much better idea that accomplishes substantially the same thing as a wall. ----------------------------------- When we talk about supporting granite we are talking about one thing. Limiting the tensile pressures. Granite, just like concrete, has great compressive strength and rotten tensile strength, when granite flexes you get compressive force on the concave side and tensile force on the convex side. Moving from theory to reality in granite we really have to do three things, (1) limit flex, (2) limit movement and (3) avoid isolation. Many inexperienced people will address movement and flex while ignoring isolation and when that happens you get the result that Joseph posted above. If we look at the brackets that are often used for granite islands we can see that their real purpose isn't to stop movement but to avoid creating a fulcrum so that the entire sheet of granite moves together. http://www.countertopbracket.com/countertop-island-support-brackets-hidden-p/ib.htm I guarantee you that something heavy placed on that overhang will cause the countertop to tip slightly in that direction, but the brackets ensure that the movement is carried past the edge of the cabinets so that the entire piece moves rather than creating a fulcrum at the back of the cabinets that isolates the overhang from the cabinets. Too much movement must be avoided because then you get the shock of the cabinets moving which can be bad so walls in long islands may be necessary but when they are you must avoid isolating them. In other words, in Joseph's example above had the brackets been extended and tied into the cabinets in such a way that the entire piece was tied together or tied to the cabinets sufficiently that everything moved together, the break is unlikely to have occurred. Technically the brackets in Joseph's post above did exactly what they were designed to do. They eliminated breakage at the fulcrum...They just created a new fulcrum because their designer didn't understand the problem. From a physics stand point, a post is nothing but a very short wall. You can get substantially the same results from a post that you can from a wall, by adding cost. Essentially the white arrows would be a wall while the red arrows will be a post. So long as the post doesn't flex more than a wall (which it will compress less than a wall), mechanically you can achieve the same thing. However, you create more isolation points, all of the red arrows need to either have very little movement at all, or be tied together in such a way that they move together (note the arrows actually form a circle). Achieving no movement is much harder than tying them together in such a way that the limited movement extends through the area. A 2" tubular frame under the entire granite surface would absolutely be preferred, as that is the best way to carry movement to the entire counter. My original advocacy for plate was in opposition of L brackets rather than a tubular frame, to avoid isolation. I think you can achieve much the same result with a steel plate (a 36" steel plate is roughly equivalent to about 20 brackets) but I am not opposed to a tubular frame, especially if you are going as deep as 2". Anyway, this is just my 2 cents. In the end, to evaluate the solution that your contractor is using we need to know that.
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sherilynn
15 years ago
I would use island legs. Here's an idea photo.

{{!gwi}}

Here is a link that might be useful: Site that sells different height legs
ni_2006
Original Author
15 years ago
mahlgold - we will be putting stools there. I am trying to envision what this round pedestal would look like. Do you have any examples?

Zinnah - sounds like an interesting solution. Is this something the fabricator would construct or would I need to buy it from some place?

Sherilynn - I am not crazy about the idea of legs, if I could avoid it.

By the way, my granite is going to be 3 cm. I will most likely use Bianco Romano. I am not sure if this makes any difference.

If anyone else has suggestions, please let me know. Thanks in advance!
malhgold
15 years ago
sort of like a pedestal base for a dining table. Depending on the style of kitchen, maybe in stainless or could be wood.
azstoneconsulting
15 years ago
ni 2006:

As far as the assembly that you are proposing goes, here's
my suggestions:

Here's what the Marble Institute of America's Technical Design
Manual says (pretty much THE BIBLE for the Stone Industry):

1. ANY unsupported span of 3CM slab greater than 10" needs
to have corbels or a structurally sound mechanism for support.

3. Plywood alone will not be sufficient in this application.

Here's a question for you - are you going to have a thicker
laminated edge at the perimeter if the island? Like a 6CM
edge detail? If so, you could use 1" x 1" angle iron or box stock epoxied to the underside of the stone to help support
the overhang... just a thought - it works pretty good
in unique design situations like the one you're proposing....

ALSO - is that column going in AFTER the stone, or is is already there?

IF it's already there, you'll probably have to have a seam
to accomadate getting the stone around the column...

let us know on these details - it will help making some more
accurate suggestions

kevin

Kevin M. Padden
Fabricator, Trainer and Consultant to the Natural Stone Industry
www.azschoolofrock.com
www.naturalstone101.com
ni_2006
Original Author
15 years ago
Hi Kevin,

The column is already there, so we would have to get a seam around it (I wish we could get rid of it, but it is load-bearing and expensive to move). In terms of the edge, we are going with either a pencilÂ Â orÂ 3/8"Â round edge. We were planning to get the same type of edge on the perimeter of the island as well.

I have a couple of questions about the suggestions you made. What do you mean by box stock? Is this like a base cabinet? Who builds it? Will I need to get a carpenter to make it for me?

How about the 1" x 1" angle iron? Is this the same as a L-bracket I have been reading about (I saw some info on gusseted vs. ungusseted, but I am not sure if this is the same thing as what you mentioned).

Do I need to purchase this iron and make it available for the fabricator? Is using 1" x 1" angle iron commonly known among fabricators?

Sorry for all the questions. I am really clueless and appreciate all the help!
kevinb_flyguy
15 years ago
Another option could be steel plate. We have had a couple of jobs where we used 1/4" steel plate under the stone secured to the cabinets. We have a water jet and just offset the big overhang by a few inches. This was done for people that did not want support legs obstructing the leg room underneath.
ni_2006
Original Author
15 years ago
hi all,

My contractor mentioned that the most logical solution is to get an extra side panel (3/4 inch thick) and then use that to reduce the overhang but still maintain enough room for legs to fit underneath.

Do you think that a 3/4" thick panel is strong enough to carry that much load from the granite overhang?
ne_flyingdiver
15 years ago
Where would the extra side panel be placed?
eandhl
15 years ago
Is your column round or sq? If sq., have your carpenter build a matching box about the same size or a little smaller. If round look at restaurant supply place for a round base for a small pup table. They are usually black but could be painted to blend with your kit.
ni_2006
Original Author
15 years ago
Kevin, it was good talking to you today. I am bumping the message so that you can see the size of the overhang. Thanks again!!
azstoneconsulting
15 years ago
ni 2006 -

Thanks for your kind words.....

e-mail sent

kevin

Granite Gurus - how would you support this much overhang?

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