18” needs to be built like a table with legs and stretcher bars. There isn’t enough depth to counterbalance that with steel bars only.

My island would be similarly structured as this one with "walls" on both ends. Are stretcher bars still necessary?

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I'd prefer not to have stretcher bars, if possible, and was hoping that with the extended walls serving as support on the ends, I could get by with metal rods underneath like this:

Absolutely, at 18”. And posts.

18” is as also overkill on a counter height overhang. You could drop back to the NKBA recommended 15”, and use the steel brackets, and a stretcher bar across the front. That would be fine.

While I agree that 15" is the recommended minimum for counter-height seating, that's for short to average people. If a family is tall or has long legs, 15" may not be enough. I'm speaking from experience.

At 5'10", 15" is barely deep enough for me (my knees brush the back of the cabinets). It's not deep enough for my 6'5" DH and 6'7" son. Even my 6'0" daughter's legs are a bit too long, but it's not enough of an issue that she won't sit there -- my son & DH won't sit there at all b/c it's too uncomfortable for them.

"18” is as also overkill on a counter height overhang."

And maybe it is but I want to be able to push my barstools all the way in as far as they will go. I'm afraid that 15" might limit that. Plus I want my finished island to be 54" wide (the width of my last island) so 18" is where it ends up at unless I make the pony wall thicker than 8".

Care to comment on how the island in the pic I posted above is supporting a deeper than 15" counter overhang with no stretcher bar? I'm trying to understand how all the ones I see on Houzz are supported:

Notice how the stools are out on the last pic. I would want to be able to push mine all the way in if possible.

Would the counter-balance system work? I don't know, so I'm throwing that question out to the pros. (I wish AZStoneConsulting, StoneGirl, Florida_Joshua, and others were still around.)

Maybe Joseph Corlett will chime in, too :)

Houzz is never ever a good metric to use as inspiration for safely built anything. The black kitchen doesn’t have 18”. It might be 15”, but looks more like 12”. Same with the gray kitchen. You can count the floor boards and see that it isn’t anywhere close to 18”.

Stretcher bars need not be 6” H, and visible right at the counter edge. Most often they are 3”, and are also reinforced with cross pieces, creating H grid work. Occasionally they will also use steel. To not have an interim post required the steel reinforcement. Or virtually invisible steel tubing, dogged into the properly built end caps that can accept the loads out onto them. You can design the custom steel tubing support, and then figure out how to disguise it with wood.

Counter balance only works in a 2/3-1/3 max cantilever ratio. That’s what the MIA approves. No other ratio. When you get the proportions off, the weight is too significant. The pivot point moves. To do a 18” overhang would need 36” of fully supported counter over cabinets. Then you could have really long custom steel brackets reinforced with gussets against bending. But that type of support is problematical with frameless cabinets.

Use steel L brackets ( made for countertop support) bolted to the far side of the 8” wall and extending under your overhang.

If you can’t find a source for the brackets,, any metal fabricator can custom make these out of flat steel stock.

What is your countertop material?

My island is very similar... IKEA cabinets 2 24” and 2 36”) with a pony wall along the back and the two sides, but with the standard 15” overhang. My stools do push in completely.

We have the flat steel brackets... I think there are 3 or 4. I would worry that they would be sufficient for an 18” overhang.

"using flat steel rods attached to the 8" wide pony wall?"

None. Steel on the flat is a poor countertop support. I've fixed this detail many times.

Look at your countertop as veneer over the substrate. If you can't dance a Conga line over the substrate, it isn't strong enough.

Joseph, what would be your recommendations then for a >15” overhang? Can steel tubing (not on the flat) be sufficient for the area between the ends? Is plywood needed under the countertop?

@Hillside House, can you post a pic of your island?

"Joseph, what would be your recommendations then for a >15” overhang?"

On this job, I'd have the framers nail 3/4" plywood blocking into the new walls, then have a metal fabricator weld a top and rear tab onto the ends of a 118" long 3" steel square tube painted flat black. Set the bar about 6" back from the front edge of the countertop, then screw through the tabs and drywall into the blocking. Conga proof.

"Can steel tubing (not on the flat) be sufficient for the area between the ends?" Yes.

" Is plywood needed under the countertop?"

No. Set the stone directly on the new steel rail and the cabinets please.

Thanks, Joseph! I am saving this for our future install.

lots of inaccurate data is usually exchanged on this one - i had quite a few discussions with my quartz installer on this ... bottom line - find out who manufacturers your material and go to their website and download the installation spec which will tell you what amount of support you will need for which overhang and which thickness of material.

Also depends on the material you're using - most installers apply Granite rules to quartz and they're very different materials so don't accept the stock answer if you're going quartz, it'll support much bigger overhangs than granite will.

At the end of the day - the reference material on this comes from the manufacturer of the material - so go straight to the source and don't be tempted to get opinions dressed up as facts from cabinet makers/installers who have not tested the material.

mikebone:

This island was installed per engineered stone manufacturer's installation instructions, but not by me. Although you can't see it here, it has a slight dip in the middle of the cantilever:

Manufacturers don't always know what's best for their products, however, the guys who make money from installing their products and will lose money if they get a callback, do.

Sink manufacturers say you need a 36" cabinet to install a 33" sink. You don't; I do it all the time, no callbacks. They provide clips for the installation of their sinks; clips are junk and leak.

We'd still be making joints in Corian with silicone were it up to the engineers and specifiers at DuPont. Thermoforming was invented by the guys who bought the sheets; they wrote the specs after we worked the bugs out.

You had better know what the hell you're doing if you go against the manufacturer's specifications, however, they should be considered minimums. The estone manufacturer in the above photo didn't wait around long enough to see the sag. I didn't have to, but there it was. Our customers are much more fussy than theirs.