South Carolina does not publish a frost line depth. The state adopts the International Residential Code with a long list of its own modifications, and in both the 2021 round and the 2024 round none of them touches the frost line depth row of Table R301.2(1) or the footing depth section, so the number is whatever your county or municipal building department has filled in. The state does set one number below ground everywhere: water service pipe goes at least 12 inches deep and at least 6 inches below the frost line.
South Carolina leaves the frost line depth to the local building department, which is where the number for an address comes from.
This code is identical to the 2024 Edition of the International Residential Code except for the following modifications:South Carolina State Register Vol. 50, Issue 5, May 22, 2026, Final Regulations, Document No. 5417, Building Codes Council, Chapter 8, International Residential Code, read September 23, 2026. Read it at the source
That makes the building department issuing the permit the office with the number, and it is a short call: the counter gives the depth for the address, and the same call settles whether a deck footing or a slab edge needs a footing inspection before the concrete goes in. What South Carolina does publish is below, and it is worth having in hand first.
A frost line depth turns into two separate requirements in most codes: how far a footing has to bear below grade, and how far a buried water service has to sit below the same line. South Carolina writes one of them out.
Water service pipe goes at least 12 inches deep and at least 6 inches below the frost line, and pipe left anywhere that freezes has to be insulated or heated.
In localities having a winter design temperature of 32°F (0°C) or lower as shown in Table R301.2 of this code, a water pipe shall not be installed outside of a building, in exterior walls, in attics or crawl spaces, or in any other place subjected to freezing temperature unless adequate provision is made to protect it from freezing by insulation or heat or both. Water service pipe shall be installed not less than 12 inches (305 mm) deep and not less than 6 inches (152 mm) below the frost line.South Carolina State Register Vol. 50, Issue 5, May 22, 2026, Regulation 8-1250, IRC Section P2603.5 Freezing, read September 23, 2026. Read it at the source
The air freezing index is the quantity the frost provisions of the model codes are written on: add up how far each day’s mean temperature fell below freezing over a winter, in degree days, and take the deepest run the winter managed. It measures how much cold the ground had to absorb, which is why it is the honest way to set one place beside another. Greenville is the coldest of the 3 cities on the record in South Carolina.
23degree days
average freezing index a winter
Greenville-Spartanburg (Greer)
| City | State | Freezing index | Once a century | Nights below freezing |
|---|---|---|---|---|
| Greenville | South Carolina | 23 | 79 | 59 |
| Columbia | South Carolina | 10 | 42 | 53 |
| Charleston | South Carolina | 6 | 30 | 29 |
Computed from NOAA National Centers for Environmental Information, Global Historical Climatology Network daily temperature records for each station, from 1951 onward. These are measurements of winter, not depths.
Only a handful of states answer with one number for the whole state, and they are the only codes that can be set beside each other directly. Ranked by the freezing index at their own reference cities, with South Carolina marked at 13 degree days for comparison against what those codes settled on:
Left to right, the mildest winters to the hardest. The figure on the right is what that state wrote into its code.
The nearest by winter are North Carolina at 12 inches, Massachusetts at 4 feet and Connecticut at 42 inches. That is a reading of other states’ codes rather than a depth for an address in South Carolina: soil, drainage, snow cover and local amendments all move the figure, and the building department issuing the permit is the office whose number binds.
South Carolina code read September 23, 2026 from South Carolina State Register Vol. 50, Issue 5, May 22, 2026, Final Regulations, Document No. 5417, Building Codes Council, Chapter 8, International Residential Code. Codes are amended and a local amendment can be deeper than the state figure, so the building department issuing the permit has the number that binds. Every state is on the frost line depth hub.