New Mexico sets one statewide floor of 12 inches below grade for exterior footings and publishes no frost depth table of its own, so how much deeper you go for frost comes from the local building department that issues your permit.
New Mexico leaves the frost line depth to the local building department, which is where the number for an address comes from.
Section R403.1.4 Minimum depth. Delete the text of this section and substitute with the following: All exterior footings shall be placed at least 12 inches (305 mm) below grade. Where applicable, the depth of footings shall also conform to Sections R403.1.4.1 and R403.1.4.2.Title 14, Chapter 7, Part 3, 2021 New Mexico Residential Building Code, New Mexico Administrative Code, State Records Center and Archives, 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 New Mexico 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. New Mexico writes one of them out.
Exterior footings must sit at least 12 inches below grade everywhere in the state, and the frost protection and seismic sections of the adopted code still apply on top of that minimum.
Section R403.1.4 Minimum depth. Delete the text of this section and substitute with the following: All exterior footings shall be placed at least 12 inches (305 mm) below grade. Where applicable, the depth of footings shall also conform to Sections R403.1.4.1 and R403.1.4.2.Title 14, Chapter 7, Part 3, 2021 New Mexico Residential Building Code, New Mexico Administrative Code, State Records Center and Archives, 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. Santa Fe is the coldest of the 3 cities on the record in New Mexico.
182degree days
average freezing index a winter
Santa Fe 2
| City | State | Freezing index | Once a century | Nights below freezing |
|---|---|---|---|---|
| Santa Fe | New Mexico | 182 | 539 | 159 |
| Albuquerque | New Mexico | 57 | 206 | 104 |
| Las Cruces | New Mexico | 10 | 53 | 78 |
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 New Mexico marked at 83 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 New Mexico: soil, drainage, snow cover and local amendments all move the figure, and the building department issuing the permit is the office whose number binds.
New Mexico code read September 22, 2026 from Title 14, Chapter 7, Part 3, 2021 New Mexico Residential Building Code, New Mexico Administrative Code, State Records Center and Archives. 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.