Support for counter with 23' overhang

14 years ago

My granite guy came to install our island top - during the installation, he informed me that he didn't feel comfortable with the amount of support. (Ya think??)

A picture's worth a thousand words.

There will be 5" legs supporting the extended corners of the countertop, where the granite flares out (shown in the picture). The granite is 2cm with two slabs of plywood underneath (3/4" each, I believe). The length of the top is about 110", and the total width is about 60". The cabinets are about 37" deep, which leaves a 23" overhang at the widest part.

The legs should help provide tip-over support, but I (obviously) need to support the rest, especially the center.

I have a good steel guy, and we're thinking about running some steel supports. I'm curious if you think supports could be built after the fact - if so, what material should used? We're thinking 1/4" x 3" flat iron attached to the cabinets, welded to 2" angle iron running underneath the cabinets. The part of the angle iron that runs vertically would probably be shaved down to 1/2" to 1" so it didn't protrude too far in either direction. We were thinking we would also need to reinforce at the angle (not sure about how much would be needed).

Do you think this would work? For 110" length, how many supports should be added? And how far from the edge of the counter top should the support run?

Any help would be greatly appreciated.

Thanks in advance

Featured Answer

User

14 years ago

Eric, this is a problem that should have been solved in the design phase, not after the fact. Certainly not after your granite has been installed! In fact, it's extremely negligible of the installer to not inform you that the supports had to be in place before the install. That's a BIG safety hazard right now! (NONE of my installers would have installed your granite untill you had your approved support in place!)

So, what can you do after the fact. Not a lot. Granite supports have to be designed into the cabinet infrastructure to handle the weight. If you're installing the CounterBalance type or corbels, they go best into a pony wall or a full 3/4" plywood cabinet back. Your's appears to be the standard thin "skin" that won't handle support for anything. There's always building stretcher bars to table legs to create a table style overhang, but with a curve, you're going to find that to be very difficult. I'd recommend using the table legs that you have in mind and a custom iron stretcher that follows the curve of your granite within 3" of the edge. A custom iron worker can make this decorative "wrought iron" type looking. Then mortise that into your table leg for support. I'd also have a center support going back to a couple of iron brackets that resemble corbels and back up to your cabinet backs like corbels would. On the inside of your cabinet, you'll need to install a 3/4" additional vertical back panel (and firmly attach it to all of the cabinet sides with L brackets) to accept the weight transfer. It's going to be dicy, because you're just transferrring that weight to the cabinet floor, rather than all the way down to the kitchen floor. You would have had to install 2x4 blocking under the cabinet floor at the rear to accept the weight transfer safely.

But, frankly, the best way to support this is to ask your counter guy to come and remove the granite and let you build a proper support and then reinstall the granite. That would let you install a full 3/4" plywood backing to the exterior of your cabinets and have something solid to attach any corbels or brackets to. As it is, it will always be a bit unsafe because your KD didn't plan for this and oversee it from the beginning.

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Comments (7)

ericmartineau
Original Author
14 years ago
Doh! Of course I meant a 23 INCH overhang, not a 23 FOOT overhang. That would be insane.
plllog
14 years ago
Eric, it's not your fault. On GW, for some stupid reason, if you want 23" in the subject line, you have to do 23'' (two single quotes instead of one double quote).

I was just discussing this subject with one of my contractors. You're apparently in a common position. It's too bad the support wasn't built into the island. Angle iron will work, but what are you anchoring it to? That's a lot of weight. If you don't want struts (i.e., triangle brackets), what's going to hold up the steel?

One of our theoretical ideas was to embed I bar or something like that, running the full width of the island, in the plywood, and have it all covered by a compound edge. That would mean reinstalling the top, however, and your cabinetry looks narrow enough that the bar should be tied to the cabinet too, rather than just relying on the weight of the granite to hold the cantilever.

There are all kinds of decorative corbels you can add. You might be able to compound several of them so that there's a support you can get your legs under that comes out far enough to be useful. But again, they'd need to be supported inside the cabinetry, and preferably into the floor.

Oh, wait! The legs. I forgot the legs. Those help. I'm sure brackets or cantilevers will work if they're sturdily anchored with the additional support of the legs.

Do you have any friends who are structural engineers? That's a lot of granite!
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Yes, you will still need support. Check the "Stone Information and Advice" thread for more information, but to summarize.... countertop support: Supporting the width of the countertop: You need a corbel or support every 30 linear inches of unsupported overhang Supporting the depth of the countertop: General: You need to support at least 2/3 the entire depth of the stone, so assuming you have 24" deep cabinets on one side of the island and your seating overhang is on the other side, you need the following: If your granite is 2 cm thick, then there can be no more then 6" of of unsupported span with a 5/8" subtop If your granite is 3 cm thick, then there can be no more then 10" of unsupported span - no subtop required If you need support, then to determine your corbel dimensions: . Thickness of Stone - Dimension of Unsupported Span = Corbel Dimension . i.e., an 18" total overhang in 2 cm would require a 12" corbel; the same overhang in 3 cm would require an 8" corbel If you are using a pony wall or cabinets with a depth of less than 2 times the depth of the overhang, then you need to provide support to equal at least 2/3 of the total depth of the countertop.
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Sorry Sophie. I'm out of the house due to renovations and had connectivity issues. I'm uploading a picture of the peninsula (long side and short side) and an overall layout for the kitchen. The issue is the left side cabinet under the long side opens under the peninsula, and the right side cabinet open on the side without the overhang. So I hang hang brackets on the right side cabinet back, but am concerned about the space between bracket at the very end of the left side which will be attached to the wall. It's then 24" until the back of the right cabinet. Sorry -for the duplicates - this is the short side panel that will have a corner angle bracket and no issue because all brackets can be affixed to the back of the cabinet below. This is a copy of the long side of the peninsula, where the cabinet opens under the underhang. The far left will have a bracket mounted to the wall. Any way to have a bracket before the 21" cabinet that is next ends?? with a 3" filler I'm worried that with such a deep overhang its weak to go so long without a bracket. Thanks, R
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chris45ny
14 years ago
Agree with live wire oak. Granite people should never have installed this for you without the proper support beforehand. We had similar situation where the granite would be 48" open-old laminate much lighter weight. We changed out the end 2 legs for ones much sturdier and DH built a table like support under the open 48" area. We had to do this first, get approval from the granite shop before they would even consider installation. Hope everything works out for you as it's a lovely looking island.
ericmartineau
Original Author
14 years ago
I really appreciate the advice. Seems the top needs to come off to allow for some better support to be installed. I have a few more pics that may help out:

The first shows the proportions of the part of the top supported by cabinets vs not. Also shows the approximate placement and size of the supporting legs.

A slightly higher angle, to show the curve of the granite.

A view from the dishwasher opening towards the back of the cabinets. We furred out the back of the cabinets several inches to run plumbing and electrical. As you can see, it's not exactly designed for bearing load.

The cabinet design: I think it's 1/2" mdf with basically a skin for the backing. Again, not really anything you'd want your countertop relying on.

I'm not feeling very confident about using my cabinets for an anchor. Plus, I think I have enough tip-over support from the legs. I'm more worried about the granite flexing in the unsupported areas.

What if I were to run 3/4" square steel tubing the full width of the island on each side of the sink, then ran 3/4" the length of the island directly above the legs. I would basically weld and gusset at the joints.

Would that offer enough support?

Thanks again.

BTW, I actually did call a structural engineer from a local listing. He said he could do nothing for me. Is there a certain kind I should be looking for?
plllog
14 years ago
It's the retrofit that makes it such a bother. It looks like you need expert help. That's why I suggested a friend engineer who might want to kibbitz. I'm still shocked that your fabricator just made it and dumped it on you.

You could have a whole steel framework embedded in the plywood, that stretched to all four legs and had a few cross pieces. Run steel supports down through the legs and into the concrete and bolt it all together. Add some supports behind the skin at the back of the island, also anchored into the concrete, and the whole thing is pretty well supported without considering the cabinetry. Any other kind of support, brackets and the like, would have to have support posts put into the island as well.

Your good steel guy might have good suggestions for how to handle the problem, and know what will and won't work, etc.
ccoombs1
14 years ago
I am really surprised that your installer went ahead with the install, knowing the support was not sufficient. Anything you do now is going to look like an afterthought. I think couple of steel angles or channels under the granite would be sufficient, but they should be routed into the plywood to hide them better. Otherwise, they will show. I'd make the granite folks come back and remove the granite and tell you what is needed to support it. These are perfect, but need to be installed prior to the granite.

Here is a link that might be useful: counter balance

Support for counter with 23' overhang

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ericmartineau
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Support for counter with 23' overhang

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ericmartineauOriginal Author

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ericmartineau
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