Loudoun County, VA Frost Line Depth: 24 in

Verified

24in

61 cm · 2 ft

Set in the building code Loudoun County has adopted.

Source and how we checked

Document: loudoun.gov

Climate: 115 nights a year at or below 32 °F (NOAA 1991–2020, Purcellville, 5.7 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

3 of 3nearby verified codes use the same depth
115nights a year at or below 32 °F
45%of nearby soil rated “low” for frost action (USDA)

How deep is the frost line in Loudoun County?

Loudoun County's building authority sets the frost line depth at 24 in (61 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 Loudoun County?

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

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

House or garage footing Deck footing Water service line Fence post

House or garage footing in Loudoun County: dig at least 24 in (61 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).

Minimum depths in Loudoun County with a 24 in frost line
Project	Depth	Rule
House or garage footing	24 in	Below the frost line and at least 12 in deep (IRC R403.1.4)
Deck footing (attached)	24 in	Below the frost line and at least 12 in deep (IRC R507.3)
Water service line	30 in	6 in below the frost line and at least 12 in deep (IRC P2603.5)
Fence post bottom	24 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 Loudoun County?

Average lows are at or below freezing from Dec to Feb. 115 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 24.5 °F.

NOAA 1991–2020 climate normals, Purcellville station, 5.7 mi away, elevation 510 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	24.5	25.9	32.3	42.2	51.6	61.1	65.5	63.9	56.1	44.3	34.5	28.4
High	41	44	52.6	64.5	72.9	81.4	86.4	84.7	77.8	66.3	54.9	44.7

Loudoun County has more freezing nights than 18 of the 22 other Virginia places we track. The Virginia median is 94. Coldest: Shenandoah County; mildest: Norfolk.

What frost line depth do towns near Loudoun County use?

3 official codes near Loudoun County are verified; each links to its document.

Official frost line depths near Loudoun County
Place	Verified frost line	Distance
Fairfax County	24 in	26 mi away
Alexandria	24 in	35 mi away
Shenandoah County	24 in	53 mi away

How likely is the soil in Loudoun County to heave?

Low 45%Moderate 38%High 17%

USDA rates the sampled soil around Loudoun County as 45% low, 38% moderate, 17% high for frost action (main soils: Catoctin, Eubanks, Braddock).

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 Loudoun County?

Call 811 at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Loudoun County building department.
Ask whether your project needs a permit (decks, larger sheds and footings usually do).
Dig below 24 in unless the building department tells you otherwise.
Book the footing inspection before you pour concrete.

Loudoun County at a glance

Frost line depth: 24 in
Population (2023 est.): 436,347
Mean annual temperature: 54.2 °F
ZIP codes (21): 20105 · 20117 · 20120 · 20129 · 20130 · 20132 · 20135 · 20141 · 20147 · 20148 · 20152 · 20158 · 20164 · 20165 · 20166 · 20175 · 20176 · 20180 · 20184 · 20197 · 22066