2009-04-29_PERMIT FILE - C1982056 (6)

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The following measures should be taken to reduce the damage, which could result from movement should the underslab materials be subjected to moisture changes. 1) The floor slabs must be separated from all bearing walls, columns and their foundation supports with a positive slip joint. We recommend the use of 1/2-inch thick cellotex or impregnated felt. 2) Interior non-bearing partition walls resting on the floor slabs should be provided with a slip joint, preferably at the bottom, so that in the event the floor slab moves, this movement is not transmitted to the upper structure. This detail is also important for wallboard and doorframes. A typical hung partition wall detail is shown in Figure #11. 3) A minimum 6-inch gravel layer should be provided beneath all floor slabs to act as a capillary break and to help distribute pressures. Prior to placing the gravel, the excavation should be shaped so that if water does get under the slab, it will flow to the perimeter of the slab or the low point of the excavation. We also recommend that all of the topsoil materials, be removed from beneath the floor slabs. 4) The floor slabs should be provided with control joints placed a maximum of 12 feet on center in each direction to help control shrinkage cracking. The location of the joints should be carefully checked to assure that the natural, unavoidable cracking will be controlled. 5) The underslab soils should be kept as close as possible to their in-situ moisture content. Excessive wetting or drying of these soils prior to placement of the floor slab could result in differential movement after the slabs are constructed. 6) It has been our experience that the risk of floor slab movement can be minimized by removing at least 3 feet of the expansive clays and/or bedrock materials and replacing them with a well compacted, non-expansive fill. If this is done or if fills are required to bring the underslab soils to the desired grade, they should consist of non-expansive, granular materials. The fills should be uniformly compacted in 6 to 8 inch lifts to at least 95% of the maximum standard Proctor density at or near the optimum moisture content, as determined by ASTM D-698/AASHTO T-99. The above precautions and recommendations will not prevent floor slab movement in the event the clays or claystone bedrock materials beneath the floor slabs undergo moisture changes; however, they should reduce the amount of damage if such movement occurs. If some floor slab movement and cracking is not tolerable, a structural floor system above a well-vented crawl space should be employed. • Job Number: 08-8241 NWCC, Inc. Page 6