Massachusetts fills in one frost line depth for the whole state, 48 inches, in the climatic and geographic design criteria table of its residential code, and a builder who wants to go shallower has to use a frost protected shallow foundation designed under section R403.3.
4 feet
Massachusetts's residential code sets one frost line depth for the whole state: 4 feet.
SUBJECT TO DAMAGE FROM Frost line depth 48 inches. For frost protected shallow foundations, see R403.3.780 CMR Tenth Edition Residential, Chapter 3: Building, Planning Amendments, Office of Public Safety and Inspections, 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. Worcester is the coldest of the 2 cities on the record in Massachusetts.
607degree days
average freezing index a winter
Worcester Rgnl AP
| City | State | Freezing index | Once a century | Nights below freezing |
|---|---|---|---|---|
| Worcester | Massachusetts | 607 | 1,389 | 135 |
| Boston | Massachusetts | 236 | 662 | 94 |
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 Massachusetts marked at 422 degree days for comparison alongside 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 Connecticut at 42 inches, North Carolina at 12 inches and Michigan at 42 inches. That is a reading of other states’ codes rather than a depth for an address in Massachusetts: soil, drainage, snow cover and local amendments all move the figure, and the building department issuing the permit is the office whose number binds.
Massachusetts code read September 22, 2026 from 780 CMR Tenth Edition Residential, Chapter 3: Building, Planning Amendments, Office of Public Safety and Inspections. 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.