Frost Line Depth in Oregon

How deep is the frost line in Oregon?

Oregon sets frost line depth in its state code by county: 12 / 18 / 24 inches. Find your county in the table below; the deeper value applies in the colder part of the state.

Who sets the frost line depth in Oregon?

The depth is written into Oregon’s statewide residential code, so local building departments enforce the state’s number rather than choosing their own. The quoted text below is the rule as we read it.

“The frost line depth below 2,500 feet in Jackson and Josephine Counties is 12 inches.”

State document: codes.iccsafe.org, read October 2026.

Where does Oregon publish its county design criteria?

Oregon sets frost depth by county in its Residential Specialty Code: 12, 18 or 24 inches. The Oregon Building Codes Division publishes the current county values, including frost line depth, in its Design Criteria Hub map. Below 2,500 feet in Jackson and Josephine counties, the frost line depth is 12 inches.

How deep do footings need to be in Oregon?

Exterior footings go at least 12 inches below undisturbed ground and below the depth the state code sets for your county, measured to the bottom of the footing. The residential code (IRC R403.1.4.1) also accepts a frost-protected shallow foundation, a design to ASCE 32 or solid rock in place of digging to the frost line, and it exempts small free-standing accessory buildings: light-frame ones up to 600 square feet with eaves 10 feet high or lower. Oregon may amend these rules, so confirm them with your building department. More detail: footing depth.

How deep should deck footings and fence posts be in Oregon?

A deck attached to the house needs footings below the depth the state code sets for your county. Under the 2021 and 2024 IRC a free-standing deck needs footings only 12 inches deep, and the 2018 edition exempts free-standing decks from the frost rule, so the answer depends on the edition Oregon adopted. See deck footing depth.

The residential code sets no fence-post depth, and fences up to 7 feet tall are exempt from a building permit (IRC R105.2), though zoning still applies. A common practice is to bury about half the above-ground height, and to reach the frost line when posts are set in concrete. See fence post depth.

How deep are water lines buried in Oregon?

Under the IRC plumbing rule (P2603.5), a water service line goes at least 12 inches deep and at least 6 inches below the frost line. States that use the Uniform Plumbing Code or their own plumbing rules word this differently, so ask your plumbing inspector which code applies in Oregon. See water line depth.

How cold do Oregon winters get?

Across the 23 Oregon places we track, nights at or below 32 °F range from 11 a year in Lincoln County to 231 in Deschutes County. The average low in the coldest month runs from 18.6 °F in Klamath County to 38.4 °F in Clatsop County (NOAA 1991–2020 normals, nearest station). Colder winters drive frost deeper in a hard year, but the code depth does not change with the weather. See frost penetration depth.

How do Oregon soils affect frost heave?

The USDA soil survey rates how prone soil is to frost action. Around the 23 Oregon places we sampled, the main rating is low at 17 places, none at 3 places, high at 2 places and moderate at 1 place. Fine, wet soils rated moderate or high heave the most, so drainage and clean gravel backfill matter more there. The rating does not change the code depth. See frost heave.

How do you confirm the frost line with your Oregon building department?

1. Find your city or county in the table above, or enter your ZIP code; a ZIP can cross into a second county.
2. Ask the building department what frost line depth it uses for Table R301.2, measured to the bottom of the footing, and whether it has local rules for decks, sheds or fences.
3. Ask the plumbing inspector how deep water and sewer lines must go.
4. Call 811 a few days before you dig so buried utilities are marked.