Frost Line Depth in Nampa, Idaho
- Nampa’s adopted code
- Checked Oct 2026
- Sources
Verified
24in
61 cm · 2 ft
Set in the building code Nampa has adopted.
Source and how we checked
Document: cityofnampa.us
Climate: 132 nights a year at or below 32 °F (NOAA 1991–2020, Nampa Sugar Factory, 1.4 mi).
Checked Oct 2026. Report a correction
How deep is the frost line in Nampa?
"{confirmed quote}". Footings, piers and other permanent supports must reach at least this depth (IRC R403.1.4.1).
Who sets the frost line depth in Nampa?
Idaho leaves the frost line depth to each city or county, and Nampa fills it in when it adopts the residential code. The value above comes from Nampa’s own document on cityofnampa.us. Canyon County uses the same 24 in, so the depth does not change at the city limits. See how Idaho sets frost line depth.
How deep do footings, decks and water lines need to be in Nampa?
House or garage footing in Nampa: dig at least 24 in (61 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).
| 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 Nampa?
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Average lows are at or below freezing from Nov to Mar. 132 nights a year reach 32 °F or colder; Dec is coldest, with an average low of 22.8 °F.
NOAA 1991–2020 climate normals, Nampa Sugar Factory station, 1.4 mi away, elevation 2,470 ft.
Monthly temperatures as a table
| °F | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low | 23 | 26 | 31.6 | 36.1 | 44 | 51 | 57.3 | 55.5 | 46.5 | 36.5 | 28.4 | 22.8 |
| High | 39.5 | 47.2 | 57.4 | 64.5 | 73.9 | 82.8 | 93.3 | 91.6 | 81 | 66.6 | 50.7 | 40 |
Nampa has fewer freezing nights than 6 of the 13 other Idaho places we track. The Idaho median is 132. Coldest: Madison County; mildest: Canyon County.
What frost line depth do towns near Nampa use?
2 official codes near Nampa are verified; each links to its document.
| Place | Verified frost line | Distance |
|---|---|---|
| Meridian | 24 in | 8 mi away |
| Canyon County | 24 in | 8 mi away |
How likely is the soil in Nampa to heave?
USDA rates the sampled soil around Nampa as 84% low, 16% moderate for frost action (main soils: Power, Purdam, Oliaga).
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 Nampa?
Nampa at a glance
- Frost line depth
- 24 in
- County
- Canyon County
- Population (2023 est.)
- 114,268
- Mean annual temperature
- 52 °F
- ZIP codes (3)
- 83651 · 83686 · 83687