Guides / Fences and walls · Updated
Frost line depth by state
Your city or county sets the real number. Call the building department before you dig.
Short answer
About 12 in across the South, 30 to 42 in through the middle of the country, and 48 in or more up north. Northern Minnesota and parts of Maine go 60 in. No footing goes shallower than 12 in anywhere.
Why there's no single number per state
The house code leaves frost depth blank. Each town fills it in. Only a handful of states set one number statewide, and those rows say so. Every other row is one real town or county's number, so you can see the ballpark. Yours can be different.
Frost depth by state
| State | Depth | Where it comes from | Source |
|---|---|---|---|
| Arizona | 0 to 24 in | Example: South Tucson. 0 below 4,000 ft, 24 above. The 12 in minimum still applies | South Tucson IRC amendment |
| Arkansas | 12 in | Example: Little Rock | City of Little Rock design criteria |
| California | 12 in | Example: Walnut Creek. Mountain towns go deeper | Walnut Creek climatic criteria |
| Colorado | 36 in | Example: Douglas County. Aurora also 36 | Douglas County code amendments |
| Connecticut | 42 in | Example: Meriden | City of Meriden design criteria |
| Delaware | 32 in | Example: New Castle County | New Castle County footing checklist |
| Florida | 12 in | Statewide minimum. No frost table | Florida Building Commission BI 214 |
| Georgia | 12 in | Example: Floyd County. Counties run 5 to 18 | Floyd County |
| Idaho | 24 in | Example: Boise | Boise City Code |
| Illinois | 42 in | Example: Harvard, northern Illinois | City of Harvard |
| Indiana | 30 to 36 in | Example: Greenwood 30, Lake County 36 | City of Greenwood |
| Iowa | 42 in | Example: Johnson County, attached decks | Johnson County deck handout |
| Kansas | 36 in | Example: Salina | Salina structural design factors |
| Kentucky | 24 in | Example: Georgetown and Scott County | Georgetown design table |
| Maine | 60 in | Example: Bangor. Winslow also 5 ft | City of Bangor |
| Maryland | 24 to 30 in | By county. Queen Anne's 24, Montgomery 30 | Montgomery County design criteria |
| Massachusetts | 48 in | Statewide | 780 CMR residential chapter 3 |
| Michigan | 42 in | Statewide. Your building official can change it | Mich. Admin. Code R 408.30522 |
| Minnesota | 42 or 60 in | Statewide. 42 in the south, 60 in the north, set by county | Minn. Rule 1303.1600 |
| Montana | 36 to 48 in | Example: Belgrade. 36 one-story, 48 two-story | City of Belgrade design criteria |
| Nebraska | 36 in | Example: Lincoln, deck footings | Lincoln deck brochure |
| Nevada | 24 in | Example: Washoe County, Reno, Sparks | Washoe County design requirements |
| New Hampshire | 48 in | Example: Alton and Durham | Town of Alton design criteria |
| New Jersey | 36 in | Example: Nutley | Nutley deck requirements |
| New Mexico | 16 in | Example: Albuquerque | City of Albuquerque |
| New York | 42 to 48 in | Set by each town. Ithaca 48, Penn Yan 42 | Town of Ithaca design table |
| North Carolina | 12 in | Statewide minimum. Mountain counties go deeper | High Point, quoting NC code AM102.1 |
| North Dakota | 54 in | Example: Fargo | Fargo deck handout |
| Ohio | 32 in | Example: Moraine, Dayton area | City of Moraine plan review |
| Oklahoma | 18 in | Example: Stillwater | Stillwater construction standards |
| Oregon | 12 to 18 in | Example: Washington County 12, Deschutes County 18 | Washington County design criteria |
| Pennsylvania | 36 in | Example: Lower Providence Township | Lower Providence Township |
| Rhode Island | 40 in | Statewide, for decks | 510-RICR-00-00-2 |
| South Carolina | 12 in | Example: Charleston lists 0. The 12 in minimum still applies | City of Charleston |
| Texas | 12 in | Example: Lubbock | City of Lubbock |
| Utah | 30 in | Example: Salt Lake City | SLC Building Services |
| Virginia | 12 in | Example: Newport News. Northern Virginia goes deeper | Newport News design criteria |
| Washington | 12 to 24 in | Example: Mason County 12, Spokane 24 | Spokane frost depth policy |
| Wisconsin | 48 in | Statewide. Below frost or 48, whichever is deeper | Wis. Admin. Code SPS 321.16 |
| Wyoming | 36 in | Example: Casper, measured to the top of the footing | City of Casper |
Depth is to the bottom of the footing below finished grade, unless the row says otherwise. Bold is a statewide number. We couldn't find an official number for Alabama, Alaska, Hawaii, Louisiana, Mississippi, Missouri, South Dakota, Tennessee, Vermont, West Virginia, so they're left off. The 12 in minimum still applies there.
Does a deck footing have to go below frost?
Yes, under the 2021 house code. There's one exception. A free-standing deck of 200 sq ft or less, sitting on pier blocks at grade, with the floor no more than 20 in up, can skip it. Some towns change that rule, so ask.
Fence posts
The code doesn't set a frost depth for fence posts. A post that stops short of frost can heave, though. If a gate post has to stay put, take it below the line.