My daughter wants me to build her a Kitchen Island that will be approx
11' by 8' ( L shaped). It will hold a stove top and will have a back
splash behind it. On top of the back splash she wants to have a
granite Counter top. My concern is what is going to hold up the 1 foot
over hang that she wants to have. I am sure that I can make the back
splash approx 6" wide but what should I use to hold up the over hang?
if she wants it to look like it's floating with no support, I'd have
brackets welded up from square steel tube and sandwich the tubes
between layers of backsplash and granite top.
if she's ok with visible brackets, go ahead and buy, make or steal
something that works with the rest of the design of the piece and her
That was my reaction at first, but thinking about it I'm getting the
impression that he's talking about a short counter on the back side of
the island, 18 inches wide with only 6 inches of structure underneath.
Steel should be holding up the overhang. Various stone people will
tell you that the maximum overhang is anywhere from 6" to 12". It's
granite, it's expensive and not a DIY repair, you might have somebody
who doesn't know any better put their full body weight on it - be
Here's a reasonable workup on the matter, with one caveat. One poster
mentioned cutting into the granite to install steel rod. You don't
want steel rod, and it's nuts to weaken the granite to make it
stronger. Further down the page is a picture of some plate steel
strips let into the plywood sub-counter - a _far_ preferable
In short, you need a design that incorporates support, but not knowing your
design, it is almost impossible to advise you.
I would draw up a proposed plan and head to a local cabinet shop and see
what they advise based on your drawing. Here's why:
IME, and simply put, you need _support_ of some type for the overhang,
regardless of the material you are using for your countertop.
A 3/4" plywood substrate is quite sufficient to support a 3/4" thick granite
"countertop" overhang of 12", providing the plywood substrate is
sufficiently deep (front to back) to be properly "cantilevered" from the
supporting base/island cabinet.
In doing a granite overhang on an island, I try to use the old "1/3 to 2/3"
cantilever rule as a bare minimum, and much more if I can get away with it:
IOW, as a MINIMUM for 12" overhang, I want at least 36" of granite over +/-
36" of well fastened plywood substrate, supported by a minimum of 24" of
Your problem is that your "countertop", in this case the top of your
backsplash, is only 6" deep and you're attempting to "cantilever" 12" of a
roughly 18" deep slab of granite.
You're concept of how a cantilever works is okay if you're talking
about materials with the same modulus of elasticity. Unfortunately
wood and granite behave far differently. Wood and plywood can take a
fair amount of flex. Granite has no such flexibility. A 3/4" plywood
sub-counter is certainly "strong" but it is not stiff in the way
granite is stiff, and it is brittle. In other words the plywood will
simply flex and the granite will be forced to take all of the load and
it will crack. It doesn't matter how far back that plywood sub-
counter extends, it will not change the amount of flex as it can not
change the modulus of elasticity of either material.
If you want to omit knee braces, corbels or any other type of visible
support, you need a stiffer material with a higher modulus - steel.
The steel should be thick enough that you can stand on the end of its
full cantilevered length. In other words the steel supports should be
designed to take _all_ of the load so that the granite can do what it
is there for - look pretty - without being required to be structural
Robatoy's suggestion of using a thicker, engineered (man-made) stone
with let-in steel is certainly a good way to go, but it is also
frequently a more expensive way to go as letting into the stone
requires more labor and entails more risk. The thicker stone adds a
lot more weight to the countertop, which may or may not be a problem
structurally, and you're paying for that extra stone that you'll never
see. The engineered stone also limits the choices you'll have in
stone. The idea is to add strength and stiffness. Cutting into a
thin slab creates stress concentration points, and let-in braces are
weakening the stone in order to strengthen it - that doesn't make
sense to me.
R's comment about idiots doing stupid things on stone cantilevered
countertops should not be discounted. I once swung a hammer at an
idjit painter's ankles that was _standing_ on the cantilever! He
jumped off, and started yelling at me, and I told him that the only
reason I didn't swing at his head was because I couldn't reach it.
Cantilever's are one of the few things where I tell people to
purposefully over-build things, as deflection and stiffness are of
paramount importance. Doubly so with a stone countertop.
Correct. Now apply that same standard to a plywood substrate. Just to
clad the bottom of a slab of granite would be a waste of time. If 3/4"
stone (either e-stone (quartz-based) or g-stone (genuine granite) is
used, one MUST build a support which on its own will support the load.
The 3/4 stones are NEVER allowed to take a structural role in a
cantelevered application. 'Real' granite is full of fissures and can
snap at any time... the risk of 'fissures' is virtually non existant
in e-stone. A 12" overhang is safe in 1 1/4" e-stone..ASSUMING the bar
top is anchored in such a way that it can't tip on a fulcrum further
away than 1/3 from the load. (That is a guide-line.) If the top is 18"
wide, I would spec a support at 6" and 12" along it's length no
further than 24" apart.
The support at the opposite edge from the load can be closer than 6"
from the edge.
Any stone shop worth its salt can let in a 1/2" thick metal bracket
with sufficient radii along the sides and end of the slot to minimize
stress-risers. The thicker material won't require a glued-on (visible
line) edge and an added edge in a flexing situation like a bar top is
not a good idea. All the dicking around to properly support a 3/4"
slab will evaporate the savings in materials quickly.
So, even though one is not supposed to count on a structural component
in a floating application, it sure is nice when the strength is there
to begin with.
The increased weight is a worthwhile investment to get the strength
and stiffness. Not to mention a much better look.
In granite, 3/4" is a non-starter. An invitation to disaster in a
suspended bar application. As I mentioned before, the investment to
properly support that brittle shit would be way more money than an
upgrade to 1-1/4"
I have 21 choices in my granite palette, but 60 in Quartz. The
uniformity of the patterns and non porous surface AND it's raw
strength make for a far more durable surface than granite.
When hit with a very hot pan, the possibilty of moisture in granite
can create quite a catastrophic failure.
Doesn't to me either. The letting in of a bracket will only be doable
in 1-1/4" e-stone material.
When using 3/4". make sure that clown can tapdance on the substrate
before you apply that thin skin of granite. 3/4" is for low-cost
I use assorted engineering programs for figuring deflection and such.
With a 350 pound load on 3/4" plywood on a 24x24 base, the deflection
is less than a 1/16th. You are conservative and I'd never dream of
telling you that was a bad thing.
Right. In that link I posted some of the replies indicated it was
possible to cantilever the stone by itself. That's a bad idea until
you get into thick stuff, 2"+ depending on the stone, which would not
be suitable for a countertop.
The 1/3 cantilever rule of thumb is fine for wood joists and such, but
it's misleading as soon as you change materials or have dissimilar
materials trying to act in concert. I pointed that out to someone and
they got mad.
With just that one comment you've made it clear you know what you're
talking about. I don't doubt that you'd do a fine job letting in for
a brace/bracket. It's not _you_ I'm worried about. You and I both
know that some "stone" guys would hog out a let in brace with their
wet skilsaw and knock out the pieces with a hammer - no one would ever
see it, right? In general, most people asking the question about how
to support a stone cantilever wouldn't know what to avoid. You do.
I thought we agreed that there should be no flexing in the stone at
Out of curiosity, what's your ballpark percentage upcharge going from
3/4" with a laminated edge to 1 1/4" granite?
Okay, we did agree. Thought I was losing my mind for a second! I
can't argue with you there.
You may be right, but what's your opinion on the suitability of the
OP's island with respect to his floor capacity? Right - I don't know
either. When I hear of an L-shaped 8' x 11' island, I think of
possibly exceeding the floor's design load. Personally, I think the
OP shouldn't go a step further until he determines what the floor is
designed for and how this, presumably fully loaded, island will affect
deflection and bounce. Your 1 1/4" engineered stone top alone would
weigh almost 550 pounds and that's on only 34 SF of floor. The
standard design load, live and dead loads, for a first floor is on the
order of 55 PSF. 15 PSF for the structure, ~15 PSF for your
countertop, leaves only 25 PSF reserve for cabinets and contents,
appliances and people. That island could _easily_ exceed the
allowable floor load. At the very least you'd have lots of deflection
and a bouncy floor.
It sounds like you're a dedicated stone installer. I'm not. I gotta
buy the stuff, and it's easier and cheaper for me to cut the plywood
and add some steel bracing as required. Of course I am not locked
into the plywood as any such decision must be based on the stone used.
No argument about the homogeneity and overall durability of the
engineered stone, but some people _like_ the random swirls and
patterns of real stone. And face it, no one's ever come to you and
said, "I don't care how it looks, I just want it to last forever."
The choice of stone vs. laminate or Corian is an aesthetic decision.
I can't tell people what to like. I can only warn them of the
consequences, and in that we're on the same page.
I'm kind of surprised that you only have 21 natural granites. Since
China and India opened up the floodgates the choices are almost
unlimited. Are the 21 granites your way of keeping your life simple
and not overwhelming customers?
It flashed across my mind when the idjit painter was up there that I
didn't want to hit his toes, which was my first thought. I figured
he'd pull his foot away and I'd bust up the countertop, so I swung at
his ankles. :)
In your rush to show us your ass, you missed the point entirely.
In the OP's case, the advice of applying a rough approximation of the
cantilever principle has NOTHING to do with "dissimilar materials" and
EVERYTHING to do with attempting a 12" overhang from a 6" counter top!!
Since you missed/ignored it, know that your new hero, who's ass you've been
kissing publicly in this thread, clearly stated the same thing:
The concept of the wREC is not to attempt to blow us away with "wordy" (your
own admission), self imagined intellect, but to provide _practical_ advice
for the OP to use in solving his problem.
Try to keep that in mind ...
You're acting like a little kid.
Bridger gave the correct answer immediately, which was essentially
That's not exactly it, but it does show the _only_ way the OP could
support such a raised top above a backsplash, and as Bridger noted, it
could be sandwiched inside to conceal it.
I went off on a tangent, agreed, but the first answer the OP got was
correct. What did I need to add to that? The thread drifted - like
that's never happened before.
I was responding to _your_ comments about cantilevering as they are
"A 3/4" plywood substrate is quite sufficient to support a 3/4" thick
"countertop" overhang of 12", providing the plywood substrate is
sufficiently deep (front to back) to be properly "cantilevered" from
supporting base/island cabinet."
Quite sufficient? Really? Using plywood to support stone is
insufficient in any cantilever situation.
And you wrote this:
"In doing a granite overhang on an island, I try to use the old "1/3
cantilever rule as a bare minimum, and much more if I can get away
That's where the dissimilar materials come in. The plywood over the
base cabinets can be infinitely stiff and the freeboard end of the
plywood cantilever will still deflect more than the granite. You need
to come up with a new rule of thumb - like don't use wood to support a
thin stone slab cantilever.
I've read enough of your posts to know that generally you do know
exactly what you are talking about. This was not one of those times.
I was not trying to piss you off. If someone is in error, it _should_
be pointed out. You do it all of the time. I learn as much as I
instruct on most newsgroups, and I like that part, even if sometimes
the learning is at my expense.
BTW, Robatoy doesn't jump down someone's throat if they disagree with
him. He treats me with respect, I treat him with respect. Unless you
have something of a technical nature to add to the OP's question,
instead of defending your wounded pride, is it okay if we just let
this thread die? Thanks.
Like all blanket statements, both erroneous and demonstrating a basic
misunderstanding of engineering and construction techniques.
You're correct on one count, however ... with that, no more needs to be
After 20+ years of manufacturing and installing countertops in all
kinds of acrobatic applications, the only failures I have encountered
have been human failure. Like the kid doing his girlfriend on the bar
section when mom & dad are away. 10 feet of 18" wide granite will
crush just about anything on the way down from bar height. The static
load isn't what concerns me most. It's that guy who tosses 3 cased of
beer on the very corner of a bartop who makes me over-engineer
structural integrity. That includes the people who will buy that house
I strongly recommend large angular brackets at strategic intervals.
They can be physically smaller when you use tubular steel.
They do not have to reach all the way to the edge of the bar, the
distance of setback depends on whether you plan on using 3/4" or
Engineered stone is much more reliable in this application, btw.
Along with other many good points, Swingman hit it right on the nose
when he discussed cantilevering. The brackets move the tipping point
Countersinking 1/2" steel brackets into 1-1/4" engineered stone is by
far the slickest look.
E-mail me a sketch and I'll post some ideas back to you.
I certainly don't claim to be a cabinet maker or solid surface guru,
but had some experience years ago in the metal trades. Quarter inch by
18 inch steel plate is about $150 for 8 foot lengths (google it). Have
a local shop or friend weld some brackets on it to attach it to your
cabinet frame to avoid tipping with the cantalever and you should be
able to dance on it. Hold it an inch or so back from the underside
edge of the granite and it is almost invisible. HTH
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