Alexandria, VA Frost Line Depth: 24 in

Verified

24in

61 cm · 2 ft

Set in the building code Alexandria has adopted.

Source and how we checked

Document: media.alexandriava.gov

Climate: 60 nights a year at or below 32 °F (NOAA 1991–2020, Washington Reagan Airport, 3.3 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

1 of 2nearby verified codes use the same depth
60nights a year at or below 32 °F
49%of nearby soil rated “high” for frost action (USDA)

How deep is the frost line in Alexandria?

Alexandria'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 Alexandria?

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

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

House or garage footing Deck footing Water service line Fence post

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

Minimum depths in Alexandria 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 Alexandria?

Average lows are at or below freezing from Jan to Feb. 60 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 30.1 °F.

NOAA 1991–2020 climate normals, Washington Reagan Airport station, 3.3 mi away, elevation 10 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	30.1	31.8	38.6	48.4	58	67.5	72.4	71	64.1	52.2	41.6	34.5
High	44.8	48.3	56.5	68	76.5	85.1	89.6	87.8	80.7	69.4	58.2	48.8

Alexandria has fewer freezing nights than 16 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 Alexandria use?

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

Official frost line depths near Alexandria
Place	Verified frost line	Distance
Fairfax County	24 in	10 mi away
Spotsylvania County	18 in	54 mi away

How likely is the soil in Alexandria to heave?

None 36%Moderate 15%High 49%

USDA rates the sampled soil around Alexandria as 36% none, 15% moderate, 49% high for frost action (main soils: Urban land, Kingstowne, Sassafras).

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 Alexandria?

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

Alexandria at a glance

Frost line depth: 24 in
County: Alexandria city
Population (2023 est.): 155,230
Mean annual temperature: 59.3 °F
ZIP codes (8): 22206 · 22301 · 22302 · 22304 · 22305 · 22311 · 22312 · 22314