Frost Line Depth in Merrimack County, NH: Nearby Codes Require 48 in

No official local value

No official frost line depth is published for Merrimack County.

Nearby official codes require 48 in (2 verified codes).

Source and how we checked

We searched this place’s own code and website and found no published frost line depth.

Climate: 171 nights a year at or below 32 °F (NOAA 1991–2020, Salisbury, 4.7 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

48 in2 verified codes within 39 mi
171nights a year at or below 32 °F
44%of nearby soil rated “high” for frost action (USDA)

Does Merrimack County have an official frost line depth?

No adopted frost line depth found for Merrimack County in its official documents (checked Oct 2026). The nearest official values, from codes we verified, are 48 in. Use the deepest of them until the building department confirms Merrimack County’s own number.

What frost line depth does Merrimack County use for footings under Table R301.2(1)? Is it 48 in, like Concord?

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

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

Drawn with the deepest nearby official value (48 in). Confirm Merrimack County’s own depth before you dig.

House or garage footing Deck footing Water service line Fence post

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

Using the nearby official value of 48 in until Merrimack County confirms its own
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 Merrimack County?

Average lows are at or below freezing from Nov to Apr. 171 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 13.2 °F.

NOAA 1991–2020 climate normals, Salisbury station, 4.7 mi away, elevation 550 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	13.2	14.7	22.3	30.8	41.1	51.2	56.6	54.6	46.2	36.1	28.9	19.7
High	31.1	34.4	42.3	55	66.7	74.9	80.2	78.6	71.2	58.4	46.6	36.1

Merrimack County has fewer freezing nights than 2 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 Merrimack County use?

2 official codes near Merrimack County are verified; each links to its document.

Official frost line depths near Merrimack County
Place	Verified frost line	Distance
Concord	48 in	8 mi away
Nashua	48 in	39 mi away

How likely is the soil in Merrimack County to heave?

Low 22%Moderate 34%High 44%

USDA rates the sampled soil around Merrimack County as 1% none, 22% low, 34% moderate, 44% high for frost action (main soils: Croghan, Metacomet, Naumburg).

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

Merrimack County at a glance

Frost line depth: No official local value
Population (2023 est.): 157,103
Mean annual temperature: 45.4 °F
ZIP codes (31): 03046 · 03104 · 03106 · 03216 · 03220 · 03221 · 03224 · 03229 · 03230 · 03231 · 03233 · 03234 · 03235 · 03242 · 03243 · 03255 · 03257 · 03258 · 03260 · 03261 · 03263 · 03268 · 03273 · 03275 · 03276 · 03278 · 03287 · 03301 · 03303 · 03304 · 03307