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<br /> <br /> 9 Parsons-1-01 <br /> <br /> <br />7.7.3 Footing Reinforcement <br />Reinforcement for footings should be designed by the structural engineer based on the <br />anticipated loading conditions. Footings for lightly loaded wood-frame structures that are <br />supported in low expansive soils should have No. 4 bars, two top and two bottom. <br />7.8 CONCRETE SLAB ON-GRADE <br />Concrete slabs will be placed on undisturbed natural soils or properly compacted fill as <br />outlined. Moisture content of subgrade soils should be maintained near the optimum moisture <br />content. <br />At the time of the concrete pour, subgrade soils should be firm and relatively unyielding. Any <br />disturbed soils should be excavated and then replaced and compacted to a minimum of 90 <br />percent relative compaction. Slabs should be designed to accommodate low expansive fill <br />soils. The structural engineer should determine the minimum slab thickness and reinforcing <br />depending upon the expansive soil condition intended use. Slabs placed on low expansive soils <br />should be at least 4 inches thick and have minimum reinforcement of No. 3 bars placed at mid- <br />height of the slabs and spaced 18 inches on centers, in both directions. The structural engineer <br />may require thicker slabs with more reinforcement depending on the anticipated slab loading <br />conditions. <br />Per CALGreen Code, a 4-inch thick base of ½ -inch or larger clean aggregate shall be provided <br />with a vapor retarder in direct contact with concrete and a concrete mix design which will <br />address bleeding, shrinkage and curling shall be used. Alternatively, concrete floor slabs should <br />be underlain with a moisture vapor retarder consisting of a polyvinyl chloride membrane such <br />as 10-mil Visqueen, or equivalent. All laps within the membrane should be sealed, and at least <br />2 inches of clean sand should be placed over the membrane to promote uniform curing of the <br />concrete. To reduce the potential for punctures, the membrane should be placed on a pad <br />surface that has been graded smooth without any sharp protrusions. If a smooth surface can not <br />be achieved by grading, consideration should be given to placing a 1-inch thick leveling coarse <br />of sand across the pad surface prior to placement of the membrane.