South Dakota has no statewide residential building code and no statewide frost line depth: a town may adopt the 2024 International Residential Code if it chooses, may amend it, and may not go beyond it, so the footing depth that applies to a given lot is whatever the local governing body has enacted.
South Dakota leaves the frost line depth to the local building department, which is where the number for an address comes from.
The governing body may, at any time, amend any provision of the International Residential Code. The governing body may not require the installation of a sprinkler system in a residential structure or impose any requirements that are more stringent than the requirements in the 2024 edition of the International Residential Code.South Dakota Codified Laws 11-10-12, Residential structures, Enactment of International Residential Code standards, 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 Dakota does publish is below, and it is worth having in hand first.
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. Aberdeen is the coldest of the 3 cities on the record in South Dakota.
1,843degree days
average freezing index a winter
Aberdeen Rgnl AP
| City | State | Freezing index | Once a century | Nights below freezing |
|---|---|---|---|---|
| Aberdeen | South Dakota | 1,843 | 3,629 | 179 |
| Sioux Falls | South Dakota | 1,391 | 2,820 | 164 |
| Rapid City | South Dakota | 650 | 1,664 | 158 |
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 Dakota marked at 1,295 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 Wisconsin at 4 feet, Vermont at 5 feet and Michigan at 42 inches. That is a reading of other states’ codes rather than a depth for an address in South Dakota: 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 Dakota code read September 23, 2026 from South Dakota Codified Laws 11-10-12, Residential structures, Enactment of International Residential Code standards. 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.