Nashua, NH Frost Line Depth: 48 in

Verified

48in

122 cm · 4 ft

Set in the building code Nashua has adopted.

Source and how we checked

Document: nashuanh.gov

Climate: 149 nights a year at or below 32 °F (NOAA 1991–2020, Nashua Cwsu, 1.1 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

1 of 1nearby verified codes use the same depth
149nights a year at or below 32 °F
67%of nearby soil rated “low” for frost action (USDA)

How deep is the frost line in Nashua?

Nashua'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 Nashua?

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

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

House or garage footing Deck footing Water service line Fence post

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

Minimum depths in Nashua 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 Nashua?

Average lows are at or below freezing from Nov to Mar. 149 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 13.8 °F.

NOAA 1991–2020 climate normals, Nashua Cwsu station, 1.1 mi away, elevation 180 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	13.8	15.5	24.1	34.7	46.1	55.9	61.6	59.7	52.2	38.9	29.1	19.5
High	34.5	37.5	45.3	58.4	69.4	78.7	84.7	82.7	75.2	62.3	50.5	39.6

Nashua has fewer freezing nights than 5 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 Nashua use?

One official code near Nashua is verified.

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

How likely is the soil in Nashua to heave?

Low 67%Moderate 32%

USDA rates the sampled soil around Nashua as 67% low, 32% moderate, 1% high for frost action (main soils: Canton, Windsor, Suncook).

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 Nashua?

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

Nashua at a glance

Frost line depth: 48 in
County: Hillsborough County
Population (2023 est.): 91,003
Mean annual temperature: 48.8 °F
ZIP codes (5): 03054 · 03060 · 03062 · 03063 · 03064