What is the Maximum Cantilever Overhang of a Natural Stone over the side of a Cabinet?

QUESTION

We are putting a piece of quartzite on our island which is 102” x 44”. Because the doors are 3/8” from top of cabinets, we would like to not have brackets. Can we support a 15” overhang? If not, what is the maximum? Any input is much appreciated. Thank you.

ANSWER

ANSWER - Industry standards state that for 3/4" (2 cm) thick stone you can cantilever the support 6" and for 1.25" ( 3 cm) stone you can cantilever 10".  But in no case can you cantilevered a portion of the stone that represents more than 1/3 of the width of the countertop.

It is always a good idea to support the cantilevered stone with corbelled supports.

9 thoughts on “What is the Maximum Cantilever Overhang of a Natural Stone over the side of a Cabinet?

  1. Carol M says:

    We have a similar installation question but on soapstone. We have a soapstone island counter top that will have a cantilever eating bar on top of the primary island. The eating bar will be 17” of cantilever with 8” on top of the primary counter top (25” total bar width). So, I believe we meet the 1/3 rule. My question is on the how-to install details and worried about stress on the primary island counter. The fabricator has black metal (iron?) brackets on the underneath side of stone (attached to a hidden piece of black quartz) that will bolt through the primary soapstone slab with a washer. As well, I’m assuming adhesive will be also applied in the 8” overlap area to the primary counter.
    Does this application meet standards and/or seem robust for soapstone?

    • Donato Pompo says:

      You have an unusual configuration countertop with the overlapping cantilever slabs. With the overlapping slabs the cantilever bottom slab is being subjected to a lot of weight not to mention what else it will be subjected to with plates of food on top and possibly someone who might attempt to stand on it to change a light or whatever.

      So the concern is what is the flexural strength of the soapstone and will it be adequate for all of the weight and stress it will be subjected to. Industry standards doesn’t cover this configuration and condition. The 1/3 rule of thumb is based on a single slab of stone. Soapstone is one of the weakest natural stones in terms of its physical properties, but is very chemical resistant.

      You need a natural stone structural engineer to do the calculation’s based on the physical properties of the soapstone you have and the configuration of the countertop and the potential loads it will be subjected to.

  2. Carol says:

    Thank you for the feedback. I have 2 more questions:
    1) how would I find a natural stone structural engineer in my area ( Minneapolis MN)
    2) I’m assuming a safe bet would be to do support corbels underneath the cantilever overhang that attach to the cabinet instead of the primary Island slab ?

    • Donato Pompo says:

      Yes you definitely need to add some corbels to support the cantilever stone countertop.

      I have heard of others who have used Larson Engineering out of White Bear Lake, MN, but I have never worked with them.

  3. Michel Cardinal says:

    We have an island in our kitchen that is covered with a 36“ x 62“ slab of man-made stone (quartz like, make unknown). The material is 20mm (0.79 inches) in thickness. On the long edge is a 10“ overhang (not supported by any brackets). We want to use a cantilevered child seat (see photo) for our five month old son (weighs about 16 pounds). The seat itself weighs about 10 pounds….. our question is: is the 10“ overhang strong enough to support the weight of the child and the chair (approx 26 pounds currently (but the little guy is growing quickly)? If currently safe, what do you estimate the max allowable weight load to be?

    image0.jpegimage1.jpegimage2.jpeg

    • Donato Pompo says:

      2cm (3/4″) thick stone should not cantilever more than 6 inches (150 mm). So a 10″ overhang is not acceptable for anything, and particularly for the safety of the child. It would never be recommended to attach a child seat to the edge of the stone slab and risk the safety of a child if it failed.

      You should install corbels to support that edge, but even then no one would stand behind saying that it would adequately support the dead or live load applied to that edge from the weight of a child in a child seat.

  4. Matt R says:

    Is there a standard for the tolerance in the countertop overhang?

    My quartzite countertop was installed on my vanity. The vanity is 10ft long and there is a half inch difference between the overhang of the countertop on the left side as compared to the right. When I measure from the face of the vanity to the front edge of the counter it is ~1 1/4″ on the left side and 1 3/4″ on the right. Is this within standards?

    I appreciate your help!

    • Donato Pompo says:

      There is not a specific standard regarding whether the cantilever of a quartz or natural stone countertop should have a symmetrical/equal distant overhang. Although I would expect from a standard-of-care point of view that a stone fabricator would be expected to have a uniform distant overhang on at least two opposite ends of a freestanding countertop like a kitchen island.

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