Connecticut Frost Line Depth: 42 Inches Statewide

Connecticut adopts the 2021 International Residential Code with statewide amendments, and the amended Table R301.2 fills in the frost line depth cell that the model code leaves blank. The figure is 42 inches, and it applies in all 169 cities and towns. Because the Connecticut State Building Code is adopted under Conn. Gen. Stat. § 29-252 and applies to all work for which a permit application was made on or after the date of adoption, there is no separate municipal frost depth to look up. That uniformity is unusual for frost depth but consistent with how Connecticut handles the rest of the table: the seismic design category is fixed statewide at B, weathering at Severe, and the winter design temperature at 7°F. Only ground snow load and wind speed vary by municipality, and those are handled in a separate appendix.

Footing depth is confirmed at the foundation inspection before concrete is placed. A footing that does not bear at or below 42 inches will not pass, and the work must be corrected before it proceeds. Enforcement sits with the local building official operating under the statewide code, which is why the standard does not change when you cross a town line.