You did not answer how deep the contractor needs to go to reach the frost line given in the area noted in my question you only stated that he need to go 12 inches below the frost line. How deep does he need to go to reach the fronst line in the Greensboro NC area say 25 mile radius
From the N.C. Code:
R403.1.4 Minimum depth. All exterior footings and foundation systems shall extend below the frost line specified in Table R301.2(1). All exterior footings shall be placed at least 12 inches (305 mm) below the undisturbed ground. In no case shall the bottom of the exterior footings be less than 12 inches below grade. Exception: Frost-protected footings constructed in accordance with Section R403.3 and footings and foundations erected on solid rock shall not be required to extend below the frost line. In Seismic Design Categories D1 and D2, interior footings supporting bearing or bracing walls and cast monolithically with a slab on grade shall extend to a depth of not less than 18 inches (457 mm) below the top of slab.
Table 301.2(1) is not included in the online version of the code. You can find it in your subcontractors copy of the Code, or the building departments copy. I presume the frost lines are divided into zones.
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