Breakfast bars and kitchen islands frequently had seating on one side. When granite, a hard, dense stone, is used as the counter material, the question arises as to how far the counter can extend past the cabinets.
The answer differs depending on the thickness of the stone, the grade of the stone and the type of support you may choose to install.
2 cm Thick Granite
2 cm or 3/4 inch thick granite is more readily available in some areas than thicker stones. This thinner stone must be supported even on the cabinets by an underlayment of plywood or MDF.
Any type of overhang that is not supported would eventually cause a 2 cm thick granite countertop to crack at the cabinet line. To overhang this type of granite top, always use corbels spaced 4 to 6 inches apart across the entire length of the countertop.
Alternatively, a steel plate can be installed beneath the counter and extending out to within an inch of its edge if corbels are not desired.
Grades 1 Through 3 of 3 cm Granite
Most thicker granite tops of 3 cm thick can extend 10 inches past the cabinets with no additional support. Some stones can handle being installed with a 12 inch overhang; defer to the fabricator at time of install over whether this is possible for a specific stone.
This rule of thumb is only for granite countertops that are grades 1, 2 or 3 and which have not been reinforced with resin and mesh on the backside of the stone. If a stone has obvious fissures, filled fissures or fiberglass mesh on the back, do not attempt to overhang it in this manner.
Grade 4 Granite
Grade 4 granite, which is has low tensile strength and is extremely prone to multiple fissures and weak spots should not be overhung more than 6 inches without support. While the stone may be thick enough to withstand being overhung without support up to 10 inches on its own, the stress of objects placed on its edge, or small children pulling on it may cause it to snap off at the cabinet point.
Support this stone with corbels placed within 6 inches of each end and with corbels spaced no more than 30 inches apart across its length. A steel plate can also be used to support the stone.
Granite that is well supported by either corbels or a steel plate can be extended as much as 24 inches past the cabinets. The supports must come within 4 inches of the counter's edge on all exposed sides when exceeding lengths of 10 to 12 inches.
Wooden or stainless steel corbels or a stainless steel plate that is 1/8-inch thick and bolted to the cabinets and epoxied to the stone it is supporting are all sufficient at supporting an overhang that exceeds the granite's stress points.