Maine adopts the 2021 International Residential Code statewide through MUBEC and publishes no frost depth of its own, so the number a footing or a service line has to beat is the one the municipal code office sets for your town.
Maine leaves the frost line depth to the local building department, which is where the number for an address comes from.
The following Chapters of the 2021 International Residential Code, published by the International Code Council, Inc., are hereby adopted and incorporated by reference: A. Chapters 1 - 1116-642 Chapter 5: Maine Uniform Building and Energy Code, Residential Building Code for One and Two-Family Dwellings in Maine, Bureau of Building Codes and Standards, 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 Maine 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. Caribou is the coldest of the 3 cities on the record in Maine.
1,956degree days
average freezing index a winter
Caribou WFO
| City | State | Freezing index | Once a century | Nights below freezing |
|---|---|---|---|---|
| Caribou | Maine | 1,956 | 3,079 | 182 |
| Bangor | Maine | 1,115 | 2,040 | 156 |
| Portland | Maine | 738 | 1,592 | 150 |
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 Maine marked at 1,270 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 Maine: soil, drainage, snow cover and local amendments all move the figure, and the building department issuing the permit is the office whose number binds.
Maine code read September 22, 2026 from 16-642 Chapter 5: Maine Uniform Building and Energy Code, Residential Building Code for One and Two-Family Dwellings in Maine, Bureau of Building Codes and 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.