In the past, building designs utilized bearing wall construction where large stones were installed one course at a time from grade to considerable elevations. In contrast, modern construction designs utilize relatively thin stone veneer and a variety of back-up materials from CMU to stud systems. A question often posed is how high can limestone panels be safely stacked without relieving angles.1
Compressive strength of the stone is one factor in answering this question. The minimum compressive strength of Indiana Limestone is 4000 psi. The minimum safety factor recommended by the Indiana Limestone Institute for bearing stress is 8 to 1. Allowable compressive stress is therefore 500 psi. If perfectly uniform full bearing were achieved at the bottom bed—where load is the highest—Indiana Limestone could theoretically be stacked about 500 feet high with ideal conditions. But several other factors must be considered, each of which limits this theoretical height. A partial list follows:
ILI's general rule is to recommend the weight of the stone be carried at each floor level. Relieving angles must be adequately supported by the back-up structure, and joints must be sized to accommodate actual deflection and sealant capabilities and performance.
If there are no intervening floors and assuming that bearing is adequate, that the anchoring systems have been designed and installed properly, and that the back-up structure has been appropriately designed to permit these heights, ILI offers the following maximum wall heights between gravity supports as conservative guidelines:
ILI recommends that limestone panels not be less than 2 inches thick. In all cases, regardless of how high they are to be stacked, stone panels must be sized and properly anchored to the back-up to handle wind loads, seismic loads, and other required design factors. This will sometimes require design by an experienced cladding designer. The back-up must also be properly designed to receive these loads, to permit the stacking height and for attachment of the stone anchors.
There will be instances, dictated by the situation, where stone may be safely stacked higher or should be stacked lower than indicated in these general rules. In all cases, the stone and its support and anchorage system should be properly evaluated to assure a proper and safe design.
For most installations, compressive stress or shear stress at the beds will control. But for tall stacks of thin stone, column buckling may control. Very little research or empirical data is available for this condition and ILI recommends avoiding tall stacks of thin stone.
Additional information about the use and installation of Indiana Limestone may be found in other ILI publications.
1A relieving angle is defined here as an angle designed and installed to carry the weight of the cladding material above. It has a soft relief joint below of sufficient width to assure there is no load transfer to the cladding material below. Typically a relief joint is caulked.