Frost Line Depth in Plymouth 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

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

Document: mass.gov

Climate: 120 nights a year at or below 32 °F (NOAA 1991–2020, Plymouth-Kingston, 2.4 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

120nights a year at or below 32 °F
70%of nearby soil rated “low” for frost action (USDA)

How deep is the frost line in Plymouth County?

Massachusetts sets the frost footing depth for Plymouth 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 Plymouth County?

Massachusetts writes this depth into its statewide residential code, so Plymouth 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 Plymouth County?

House or garage footing Deck footing Water service line Fence post

House or garage footing in Plymouth 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 Plymouth 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 Plymouth County?

Average lows are at or below freezing from Dec to Mar. 120 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 21.8 °F.

NOAA 1991–2020 climate normals, Plymouth-Kingston station, 2.4 mi away, elevation 45 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	21.8	23.3	29	38.4	47.9	58.1	64.1	63.2	56.8	45.8	36.4	28.3
High	41	42.8	49.1	59.2	69.1	78.5	84	82.3	75.7	65.4	55.1	45.9

Plymouth County has fewer freezing nights than 29 of the 38 other Massachusetts places we track. The Massachusetts median is 130. Coldest: Berkshire County; mildest: Malden.

How likely is the soil in Plymouth County to heave?

Low 70%Moderate 30%

USDA rates the sampled soil around Plymouth County as 70% low, 30% moderate, 0% high for frost action (main soils: Deerfield, Merrimac, Montauk).

USDA NRCS soil survey, 9 sample points within 2 mi. Higher frost action means more risk of heave; see frost heave.

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

Call 811 at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Plymouth 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.

Plymouth County at a glance

Frost line depth: 48 in (Massachusetts rule)
Population (2023 est.): 535,308
Mean annual temperature: 52.5 °F
ZIP codes (36): 02043 · 02045 · 02047 · 02050 · 02061 · 02066 · 02301 · 02302 · 02324 · 02325 · 02330 · 02332 · 02333 · 02338 · 02339 · 02341 · 02346 · 02347 · 02350 · 02351 · 02359 · 02360 · 02364 · 02366 · 02367 · 02370 · 02379 · 02382 · 02532 · 02538 · 02558 · 02571 · 02576 · 02738 · 02739 · 02770