Massachusetts Frost Line Depth: 48 Inches Statewide

Most states leave the frost line depth cell of IRC Table R301.2 blank for each city or town to fill in when it adopts the code. Massachusetts does not. The Massachusetts Residential Code replaces the model table outright with its own Table R301.2(1), and that table states a single figure, 48 inches, that applies in every one of the state's 351 municipalities. There is no local variation to look up, because 780 CMR is a statewide code and municipalities cannot amend it. The same table cell points builders to R403.3 as the alternative: a frost-protected shallow foundation, designed to the referenced method, may be used instead of excavating to the full 48 inches. Note that the frost depth is uniform even though the state's snow loads are not, Massachusetts publishes a separate per-municipality table for ground snow load and wind speed.

Footing depth is checked at the foundation inspection before concrete is placed. A footing that does not bear at or below 48 inches, and is not designed as a frost-protected shallow foundation under R403.3, will not pass that inspection, and work cannot proceed until it is corrected. Enforcement is by the local building department under its permit and inspection authority.