Wilmington, DE Frost Line Depth: 32 in

Verified

32in

81 cm · 2 ft 8 in

Set in the building code Wilmington has adopted.

Source and how we checked

Document: library.municode.com

Climate: 87 nights a year at or below 32 °F (NOAA 1991–2020, Wilmington Porter Rsch, 2.7 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

0 of 1nearby verified codes use the same depth
87nights a year at or below 32 °F
51%of nearby soil rated “none” for frost action (USDA)

How deep is the frost line in Wilmington?

Wilmington's building authority sets the frost line depth at 32 in (81 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 Wilmington?

Delaware has no statewide residential code, so Wilmington adopts its own and fills in the frost line depth. The value above comes from Wilmington’s own document on library.municode.com. See how Delaware sets frost line depth.

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

House or garage footing Deck footing Water service line Fence post

House or garage footing in Wilmington: dig at least 32 in (81 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).

Minimum depths in Wilmington with a 32 in frost line
Project	Depth	Rule
House or garage footing	32 in	Below the frost line and at least 12 in deep (IRC R403.1.4)
Deck footing (attached)	32 in	Below the frost line and at least 12 in deep (IRC R507.3)
Water service line	38 in	6 in below the frost line and at least 12 in deep (IRC P2603.5)
Fence post bottom	32 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 Wilmington?

Average lows are at or below freezing from Dec to Feb. 87 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 23.8 °F.

NOAA 1991–2020 climate normals, Wilmington Porter Rsch station, 2.7 mi away, elevation 270 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	23.8	25.2	32.3	42.5	52.4	61.8	67.2	65.7	58.6	47	36.8	29
High	37.9	40.9	49.2	61.1	70.6	79.4	84	81.9	75	63.3	52.5	42.8

What frost line depth do towns near Wilmington use?

One official code near Wilmington is verified.

Official frost line depths near Wilmington
Place	Verified frost line	Distance
Sussex County	24 in	74 mi away

How likely is the soil in Wilmington to heave?

None 51%Moderate 28%High 21%

USDA rates the sampled soil around Wilmington as 51% none, 28% moderate, 21% high for frost action (main soils: Urban land, Water, Udorthents).

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 Wilmington?

Call 811 at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Wilmington building department.
Ask whether your project needs a permit (decks, larger sheds and footings usually do).
Dig below 32 in unless the building department tells you otherwise.
Book the footing inspection before you pour concrete.

Wilmington at a glance

Frost line depth: 32 in
County: New Castle County
Population (2023 est.): 71,675
Mean annual temperature: 53.4 °F
ZIP codes (7): 19801 · 19802 · 19803 · 19805 · 19806 · 19807 · 19809