North Dakota publishes no frost depth number of its own: the state building code is the 2024 International Residential Code with amendments that touch only the frost protection exceptions, so the required depth comes from the city, county or township that adopts and enforces the code, and a reader should call that building department before digging.
North Dakota leaves the frost line depth to the local building department, which is where the number for an address comes from.
Cities, townships, and counties that elect to enforce a building code are responsible for adopting and enforcing the state building code, but may amend the code to conform to local needs.Article 108-01, North Dakota State Building Code, North Dakota Administrative Code, 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 North Dakota 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. North Dakota writes one of them out.
North Dakota keeps the International Residential Code requirement that footings extend below the frost line and amends only the exceptions, so the depth itself is set by the city, county or township enforcing the code.
Section 403.1.4.1 Frost Protection Revise and Add as follows: Exceptions: 1. Protection of free-standing accessory structures shall not be required.2024 International Residential Code Amendments, North Dakota State Building Code, North Dakota Department of Commerce, Division of Community Services, 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. Minot is the coldest of the 3 cities on the record in North Dakota.
2,330degree days
average freezing index a winter
Minot Exp Stn
| City | State | Freezing index | Once a century | Nights below freezing |
|---|---|---|---|---|
| Minot | North Dakota | 2,330 | 4,210 | 187 |
| Fargo | North Dakota | 2,251 | 4,104 | 176 |
| Bismarck | North Dakota | 1,926 | 3,744 | 185 |
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 North Dakota marked at 2,169 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 North 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.
North Dakota code read September 22, 2026 from Article 108-01, North Dakota State Building Code, North Dakota Administrative Code. 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.