Sources vary as to recommendations on what size countertop overhang requires supports and what constitutes sufficient bracing for a countertop overhang. While there appears to be few standards related to this topic the concensus established in the review of comments related to the topic show that a countertop overhang greater than 6 (or up to 10) inches needs to have additional support. It also appears to be common practice in the installation of stone
counters to allow a countertop overhang to be unsupport if not extending over 10 inches and/or if 2/3 of the total counter slab is supported by a cabinet or other sub support structure.
While not refuting the concensus, Federal Brace chooses to take a little more conserative approach to the need for countertop overhang support. We feel that there needs to be additional factors considered when determining countertop overhang support. The basic "standards" established take into account the static load of a countertop on its support structure. While static load is by far the most persistent of factors involved in carrying the load of a countertop, it is not the only factor. Some other factors may include:
- Point Load Occurances - where a heavy object or a significant force is placed on the counter at one point cause possible compromise within the stone slab itself or causing a deflection in the stone to point of cracking.
- Consistencies of Stone Character - Granite as an example has a variety of different classes (ratings) based on the individual characteristic of the granite itself including the presence of natural fissures that may cause the stone to react differently under force.
- Location and Environment - An indoor application in Kansas will be completely different from an outdoor location in California - not to mention the difference between a single family home and a frat house with table top dancing!
And one more thing to consider - though people often use supports under their countertop overhang they do not realize that their countertop braces need to have a sufficient supporting substructure and sufficient anchorage to that substructure. If this is overlooked it could be more of a problem than a solution. As an example, consider a project that uses 3 each 16" x 16" Brunswick Brackets (view here) to support a 20" overhang that extends 8 feet. If this application is entirely supported on a stud wall that is fastened to the floor than the total supporting structure incorporates the floor, studs and brackets. Now place that same application to a 3/4" thick plyboard back of a cabinet. Now the supporting structure consist of its weakest link - the plyboard - and the brackets are of little value. The board will bend and break over time and the whole application will fail.
When considering support for your countertop overhang always be conservative. It will never pay to limit your support and have a system that is either weak or will fail. The extra dollars that you spend on the support of your countertop overhang will save you some gray hair and the need to replace your kitchen countertop in the near future.
For more information on Countertop Overhang Support visit Federal Brace's Countertop Resources Area Here.