How much overhang can I have without additional support? The short answer everyone is looking for is 12 inches. The Marble institute of America recommends no more than 12 inches unsupported. This short answer is not enough as there are variables that must be understood to safely answer this question. The maximum overhang depends upon the hardness of the stone and just how much counter IS FULLY supported vs how much is not. Cantilevered weight offset, is what we are looking for.
Here is an extreme example. If you only have 6 inches of stone on top of a wall cap then the maximum safe overhang is 2 inches following the 2/3rds rule. The Marble institutes 12 inch guide line may lead someone to believe that it is OK to have 12 inches of overhang when in this situation it would immediately fall off the wall and potentially injure anyone with feet in the path of the falling granite.
So to clarify the maximum overhang is the lesser of 2/3rd or 12 inches. Even that depends upon the fragility of the material. I would not recommend a 12 inch unsupported overhang with Onyx due to how soft and fragile the material is and you can get away with 16 inches if the material was Absolute Black as the material is fissure free and extremely hard.
How much overhang can you have without additional support? This question comes up daily and affects layout and overall design of many kitchens.
The straight answer is up to 12 inches for granite, providing 2/3 or more is cantilevered to offset the unsupported weight.
Peninsula overhangs can make or break the overall functionality of a kitchen. The use of Corbels or legs to support additional overhangs can affect chairs and leg areas so finding solutions can affect the functionality of a kitchen design.
You can have more and sometimes less is recommended depending upon the actual stone. Very hard stones can safely support more overhang, providing the 2/3 cantilevered criteria is met. Softer or more fragile stones may dictate less overhang.
What options do you have if you just have to have more overhang. well there are couple different ones to consider.
Below are some of the popular solutions and options as well some pros and cons to each solution.
-Corbels- Visible but decorative
-Brackets- Inexpensive and effective, installed properly works better on wall tops than upon cabinets
themselves.
-Legs -Visible, decorative but in the way of chairs and peoples legs.
-Granite Countertop support brackets- Hidden and concealed but offers great support. They must be installed before the granite and cut into the cabinet itself. They are specifically designed for this challenge.
-Rods- Can be installed inside of the stone to strengthen and potentially extend the limit as this technique does reinforces fragile stones, but does nothing to extend the cantilever rule of 2/3rds.
Think a worst case scenario such as someone deciding to jump up on top of a countertop and ask yourself, "would that be safe" Consider the application as well. what is safe in a frat house is not the same for what is safe in a retirement community. Consider the application, material, cantilever support and err to the safe side when designing and planning the amount of overhang you might engineer into your granite countertops.
Dan DiTomaso Stone Masters Inc. http://www.stonemastersinc.net
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