Alabama publishes no frost line depth, and at the moment it has no settled statewide residential building code either. The state agency that runs the building code has no jurisdiction over houses, and the job of adopting a residential code moved to the Home Builders Licensure Board on October 1, 2024; its advisory council first met in February 2025 and a rule is still working through the approval process. Until that lands, the footing depth a builder has to meet is whatever the city or county building department requires, so ask them.
Alabama leaves the frost line depth to the local building department, which is where the number for an address comes from.
DCM does not have jurisdiction over residential property or commercial property except for hotels/motels and movie theaters. Adoption authority of the residential building code was transferred from the Alabama Department of Economic and Community Affairs (ADECA) to the Alabama Home Builders Licensure Board (ph: 334-242-2230) effective October 1, 2024 per Act 2024-443, which established an Alabama Residential Building Code Advisory Council within the newly established Alabama Residential Building Code Division that must present a code to the Board for adoption by October 1, 2025.Building Code, Alabama Division of Construction Management, 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 Alabama 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. Huntsville is the coldest of the 3 cities on the record in Alabama.
42degree days
average freezing index a winter
Huntsville Intl AP
| City | State | Freezing index | Once a century | Nights below freezing |
|---|---|---|---|---|
| Huntsville | Alabama | 42 | 146 | 61 |
| Birmingham | Alabama | 23 | 86 | 52 |
| Mobile | Alabama | 3 | 22 | 15 |
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 Alabama marked at 23 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 Alabama: soil, drainage, snow cover and local amendments all move the figure, and the building department issuing the permit is the office whose number binds.
Alabama code read September 23, 2026 from Building Code, Alabama Division of Construction Management. 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.