Concord, NH Frost Line Depth: 48 in

Verified

48in

122 cm · 4 ft

Set in the building code Concord has adopted.

Source and how we checked

Document: concordnh.gov

Climate: 165 nights a year at or below 32 °F (NOAA 1991–2020, Concord Municipal Airport, 4 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

1 of 1nearby verified codes use the same depth
165nights a year at or below 32 °F
65%of nearby soil rated “moderate” for frost action (USDA)

How deep is the frost line in Concord?

Concord's building authority sets the frost line depth 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 Concord?

New Hampshire leaves the frost line depth to each city or county, and Concord fills it in when it adopts the residential code. The value above comes from Concord’s own document on concordnh.gov. See how New Hampshire sets frost line depth.

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

House or garage footing Deck footing Water service line Fence post

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

Minimum depths in Concord 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 Concord?

Average lows are at or below freezing from Nov to Mar. 165 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 12.9 °F.

NOAA 1991–2020 climate normals, Concord Municipal Airport station, 4 mi away, elevation 346 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	12.9	14.7	23.3	33.3	44.1	53.7	59.2	57.2	49	37.8	28.7	19.5
High	31.6	34.8	43.6	57.5	69.3	77.8	83	81.7	73.7	60.9	48.4	37.1

Concord has fewer freezing nights than 3 of the 5 other New Hampshire places we track. The New Hampshire median is 171. Coldest: Sullivan County; mildest: Nashua.

What frost line depth do towns near Concord use?

One official code near Concord is verified.

Official frost line depths near Concord
Place	Verified frost line	Distance
Nashua	48 in	34 mi away

How likely is the soil in Concord to heave?

Low 32%Moderate 65%

USDA rates the sampled soil around Concord as 32% low, 65% moderate, 3% high for frost action (main soils: Windsor, Croghan, Paxton).

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 Concord?

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

Concord at a glance

Frost line depth: 48 in
County: Merrimack County
Population (2023 est.): 44,629
Mean annual temperature: 47.2 °F
ZIP codes (3): 03224 · 03301 · 03303