Maryland applies the 2021 International Residential Code statewide as the Maryland Building Performance Standards but writes no frost depth into it, leaving the number to the county or municipality that issues your permit, and each local amendment has to be filed with the Department of Labor for its central database.
Maryland leaves the frost line depth to the local building department, which is where the number for an address comes from.
Each local jurisdiction: (a) May by local amendment modify the provisions of the Standards to address conditions peculiar to the local jurisdiction's community ... (3) If a local amendment conflicts with the provisions of the Standards, the provisions of the local amendment shall prevail in the local jurisdiction.COMAR 09.12.51.05 Maryland Building Performance Standards, Code of Maryland Regulations, 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 Maryland 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. Oakland is the coldest of the 3 cities on the record in Maryland.
461degree days
average freezing index a winter
Oakland 1 SE
| City | State | Freezing index | Once a century | Nights below freezing |
|---|---|---|---|---|
| Oakland | Maryland | 461 | 1,231 | 149 |
| Hagerstown | Maryland | 203 | 625 | 110 |
| Baltimore | Maryland | 126 | 403 | 95 |
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 Maryland marked at 263 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 Massachusetts at 4 feet, North Carolina at 12 inches and Connecticut at 42 inches. That is a reading of other states’ codes rather than a depth for an address in Maryland: soil, drainage, snow cover and local amendments all move the figure, and the building department issuing the permit is the office whose number binds.
Maryland code read September 23, 2026 from COMAR 09.12.51.05 Maryland Building Performance Standards, Code of Maryland Regulations. 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.