Indiana Frost Line Depth by County: 24, 30 or 36 Inches

Indiana does not leave the frost line depth for each city to fill in. 2(1) outright and substituted its own, which lists all 92 counties with a Foundation column. Footnote c defines that column precisely: it is the minimum depth, in inches, from finish grade to the bottom of the footing. Three values are used. Thirty-six counties are at 24 inches, twenty-nine at 30 inches, and twenty-seven at 36 inches, running deeper as you move north. Lake, St. Joseph and Allen counties along the northern border are all 36 inches, Marion County is 30, and Monroe in the south is 24.

Digging below the tabulated depth is only one of four ways to satisfy the code. 3, one built to ASCE 32, or one erected on solid rock, and it bars footings from bearing on frozen soil unless that condition is permanent.

Footing depth is verified at the foundation inspection before concrete is placed, by the local building department or the state as applicable. A footing above the depth listed for its county, and not built by one of the three alternative methods the code allows, will fail that inspection and must be corrected before work continues. Freestanding accessory structures of 721 square feet or less are excepted where built in accordance with Table R309.