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22. 10 - Plain concrete in structures assigned to seismic design category C, D, E or F. 22.10.1- Structures assigned to Seismic Design Category C, D, E or F shall not have elements of structural plain concrete, except as follows: (a) Isolated footings of plain concrete supporting pedestals or columns are permitted, provided the projection of the footing beyond the face of the supported member does not exceed the footing thickness. (b) Plain concrete footing supporting walls are permitted, provided the footings have at least two continuous longitudinal reinforcing bars. Bars shall not be smaller than No. 4 and shall have a total area of not less than 0.002 times the gross cross - sectional area of the footing. A minimum of one bar shall be provided at the top and bottom of the footing. Continuity of reinforcement shall be provided at corners and intersections. Exception: In detached one and two- family dwellings three stories or less in height and constructed with stud bearing walls, plain concrete footings with at least two continuous longitudinal reinforcing bars not smaller than No. 4 are permitted to have a total area of less than 0.002 times the gross cross — sectional area of the footing. 20.08.120 CBC Section 1907.1 amended - Minimum Slab Provisions. Section 1907.1 is amended to read as follows: 1907.1 General. The thickness of concrete floor slabs supported directly on the ground shall not be less than 3'/2 inches (89 mm). A minimum 10 -mil (0.010 inch, .20mm) polyethylene moisture retarder with joints lapped not less than 6 inches (152 mm) shall be placed above a minimum of 4- inches (102 mm) of crushed or angular rock capillary moisture barrier or other approved equivalent methods and materials used to provide slab - stability and moisture protection of the interior environment of the building. The capillary moisture barrier material shall have a maximum particle size of 3/4 -inch with no more than 10 percent smaller than 1/4 —inch. In order to promote a more uniform curing of the slab and to provide protection for the polyethylene moisture retarder, a minimum of two- inches of fine clean sand shall be placed directly over the moisture retarder. As a minimum and in all cases where a slab is to be placed inside of a building, the slab shall be reinforced with not less than six inches by six inches ten gauge welded wire mesh or an approved alternate installed on approved supports at mid height of the concrete slab. Exception: A vapor retarder, sand and rock are not required: 1. For detached structures accessory to occupancies in Group R -3, such as garages, utility buildings or other unheated facilities. 2. For unheated storage rooms having an area of less than 70 square feet (6.5 m2) and carports attached to occupancies in Group R -3. 3. For buildings of other occupancies where migration of moisture through the slab from below will not be detrimental to the intended occupancy of the building and