Oklahoma adopts the 2024 International Residential Code as its statewide minimum for houses but deliberately leaves the frost line depth cell of the climatic table blank for each local authority to fill in, so the number you build to comes from your city or county building department.
Oklahoma leaves the frost line depth to the local building department, which is where the number for an address comes from.
Row 2, column 4, subcolumn 2 has been left blank for the authority having jurisdiction to complete based on local conditions as described in footnote "b." ... Footnote "b" reads: "Where the frost line depth requires deeper footings than indicated in Figure R403.1(1), the frost line depth strength required for weathering shall govern. The jurisdiction shall fill in the frost line depth column with the minimum depth of footing below finished grade."Title 748 Chapter 20 Adopted Codes Subchapter 6, International Residential Code 2024 Edition, Oklahoma Uniform Building Code Commission, read September 22, 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 Oklahoma 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. Oklahoma writes one of them out.
Oklahoma's amended plumbing section sets a 12 inch minimum cover for building sewers, including the run to a septic tank, and lets the local authority approve something different.
P2603.5.1 Sewer depth. Building sewers that connect to private sewage disposal systems shall be not less than 12 inches (305 mm) or as approved by the authority having jurisdiction below finished grade at the point of septic tank connection. Building sewers shall be not less than 12 inches (305 mm) below grade.Title 748 Chapter 20 Adopted Codes Subchapter 6, International Residential Code 2024 Edition, Oklahoma Uniform Building Code Commission, read September 22, 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. Tulsa is the coldest of the 2 cities on the record in Oklahoma.
96degree days
average freezing index a winter
Tulsa Intl AP
| City | State | Freezing index | Once a century | Nights below freezing |
|---|---|---|---|---|
| Tulsa | Oklahoma | 96 | 352 | 74 |
| Oklahoma City | Oklahoma | 86 | 314 | 75 |
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 Oklahoma marked at 91 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 Oklahoma: soil, drainage, snow cover and local amendments all move the figure, and the building department issuing the permit is the office whose number binds.
Oklahoma code read September 22, 2026 from Title 748 Chapter 20 Adopted Codes Subchapter 6, International Residential Code 2024 Edition, Oklahoma Uniform Building Code Commission. 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.