Frost Line Depth in Suffolk County, MA: 48 in (Massachusetts rule)

State-set value

48in

122 cm · 4 ft

48 in (Massachusetts rule)

Set by the state: 780 CMR (10th ed.) Table R301.2(1).

Source and how we checked

Suffolk County does not publish its own value; the state rule applies.

Document: mass.gov

Climate: 92 nights a year at or below 32 °F (NOAA 1991–2020, Boston Logan International Airport, 1.6 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

92nights a year at or below 32 °F
54%of nearby soil rated “moderate” for frost action (USDA)

How deep is the frost line in Suffolk County?

Massachusetts sets the frost footing depth for Suffolk County at 48 in (122 cm). Footings, piers and other permanent supports must reach at least this depth (IRC R403.1.4.1).

Who sets the frost line depth in Suffolk County?

Massachusetts writes this depth into its statewide residential code, so Suffolk County’s building department enforces the state’s number rather than setting its own. See how Massachusetts sets frost line depth.

How deep do footings, decks and water lines need to be in Suffolk County?

House or garage footing Deck footing Water service line Fence post

House or garage footing in Suffolk County: dig at least 48 in (122 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).

Minimum depths in Suffolk County with a 48 in frost line
Project	Depth	Rule
House or garage footing	48 in	Below the frost line and at least 12 in deep (IRC R403.1.4)
Deck footing (attached)	48 in	Below the frost line and at least 12 in deep (IRC R507.3)
Water service line	54 in	6 in below the frost line and at least 12 in deep (IRC P2603.5)
Fence post bottom	48 in	No code rule; common practice is below the frost line

Work out posts, concrete and footing sizes with the fence post depth calculator or the deck footing calculator.

How cold does it get in Suffolk County?

Average lows are at or below freezing from Dec to Mar. 92 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 23.1 °F.

NOAA 1991–2020 climate normals, Boston Logan International Airport station, 1.6 mi away, elevation 12 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	23.1	24.6	31.1	40.8	50.3	59.7	66	65.1	58.2	47.5	37.9	29.2
High	36.8	39	45.5	56.4	66.5	76.2	82.1	80.4	73.1	62.1	51.6	42.2

Suffolk County has fewer freezing nights than 35 of the 38 other Massachusetts places we track. The Massachusetts median is 130. Coldest: Berkshire County; mildest: Malden.

How likely is the soil in Suffolk County to heave?

Low 46%Moderate 54%

USDA rates the sampled soil around Suffolk County as 46% low, 54% moderate for frost action (main soils: Newport, Merrimac, Sudbury).

USDA NRCS soil survey, 18 sample points within 5 mi. Higher frost action means more risk of heave; see frost heave.

How do you confirm the frost line before you dig in Suffolk County?

Call 811 at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Suffolk County building department.
Ask whether your project needs a permit (decks, larger sheds and footings usually do).
Dig below 48 in unless the building department tells you otherwise.
Book the footing inspection before you pour concrete.

Suffolk County at a glance

Frost line depth: 48 in (Massachusetts rule)
Population (2023 est.): 768,425
Mean annual temperature: 51.9 °F
ZIP codes (39): 02108 · 02109 · 02110 · 02111 · 02113 · 02114 · 02115 · 02116 · 02118 · 02119 · 02120 · 02121 · 02122 · 02124 · 02125 · 02126 · 02127 · 02128 · 02129 · 02130 · 02131 · 02132 · 02133 · 02134 · 02135 · 02136 · 02149 · 02150 · 02151 · 02152 · 02163 · 02199 · 02203 · 02205 · 02210 · 02215 · 02445 · 02446 · 02467