Frost Depth in Spokane and Eastern Washington: How Deep Do Footings Need to Be? (2026)

Short answer: in the City of Spokane, Spokane Valley, Liberty Lake, Airway Heights and unincorporated Spokane County, footings go at least 24 inches below finished grade. Deer Park requires 36 inches. Colville, rural Stevens County and Pend Oreille County require 30 inches. That number is the frost depth, and it decides how deep we dig for every footing, foundation wall, thickened slab edge and pole-building post we set. Here is what each local code says, why it matters, and the exceptions that let some small buildings go shallower.

What frost depth means

When the ground freezes, water in the soil turns to ice and expands. That can lift, or "heave," anything resting on it, then drop it unevenly when the ground thaws in spring. Frost depth is the depth your local building department says footings must reach so they sit on soil that doesn't freeze.

• The code doesn't pick the number: the International Residential Code leaves frost depth blank in its climate table (Table R301.2), and each jurisdiction fills it in
• The code does set a floor: exterior footings must be at least 12 inches below undisturbed ground, and they must be protected from frost (IRC R403.1.4)
• Four ways to protect from frost: extend the footing below the frost line, build a frost-protected shallow foundation, design to the ASCE 32 standard, or bear on solid rock
• No pouring on frozen ground: footings can't bear on frozen soil unless the frozen condition is permanent. Spokane's seasonal frost isn't, which is one reason winter pours take extra steps. See our guide to pouring concrete in winter

Frost depth by town in the Spokane area

These are the figures published by each building department. Always confirm for your parcel, since the department that issues your permit has the final word.

• City of Spokane: 24 inches, set in Spokane Municipal Code 17F.040.105 along with a "severe" weathering rating
• Unincorporated Spokane County: 24 inches below finished grade under the City of Spokane / Spokane County joint frost-depth policy (BUILD-07)
• City of Spokane Valley: 24 inches
• City of Liberty Lake: 24 inches below finished grade, per the City's construction design criteria
• City of Airway Heights: 24 inches, per the City's geographic design criteria
• City of Deer Park: 36 inches, set in Deer Park Municipal Code 15.04.010. That's a full foot deeper than Spokane, and Deer Park also carries a 56 to 65 psf ground snow load
• City of Colville: 30 inches, measured from finished grade to the bottom of the footing
• Rural Stevens County: 30 inches minimum for footings exposed to outside temperatures, per the Stevens County building code ordinance
• Pend Oreille County (Newport area): 30 inches below finish grade, measured to the bottom of the footing, per the County's geographic design criteria

If your lot is north of Spokane, the frost line usually gets deeper, not shallower. A shop plan drawn for the Valley can be short on footing depth in Deer Park, Colville or Newport.

The exceptions: when a building can go shallower

• Small detached accessory buildings in Spokane and Spokane County: the joint BUILD-07 policy allows 18 inches for detached residential accessory buildings
• Frost-protected shallow foundations: the same policy allows them. These use rigid insulation around and under the footing to keep the soil beneath it from freezing, so the footing can sit higher. They're designed to IRC Section R403.3
• The IRC's small-building exemption: under R403.1.4.1, freestanding accessory structures of light-frame construction that are 600 sq ft or less with an eave height of 10 feet or less don't need frost protection. The limit is 400 sq ft for other construction types. Local rules can be stricter, so we check with your jurisdiction before relying on it
• Most shops don't qualify: a typical 30x40 shop is 1,200 sq ft, twice the light-frame limit, so its footings go to full frost depth

What frost depth means for each kind of project

• Steel buildings (PEMB): column footings and the perimeter grade beam go below the frost line, and anchor bolts are set into them for the frame. Our PEMB foundations guide covers what goes into that pour
• Pole buildings: each post footing sits below the frost line so frost can't jack the posts upward. Spokane County's BP-32 pole building handout also requires a footing inspection before the post holes are backfilled
• Shop and garage slabs: the slab itself sits near the surface, but a monolithic slab's thickened edge, or a separate stem wall, carries the walls down to frost depth. Compacted gravel base and drainage keep frost from lifting the middle. See how thick a shop slab should be
• Driveways, patios and walkways: flatwork floats on a compacted base rather than reaching frost depth. Air-entrained concrete, good base, slope away from the house and saw-cut joints are what keep it from heaving and cracking
• Retaining walls: wall footings are sized and set for frost as well as soil load. Our retaining wall permit guide covers when a wall needs engineering

Frost depth and snow load go together

The same department that sets your frost depth sets your snow load, and both get heavier north of town. Deer Park's 36-inch frost line comes with a 56 to 65 psf ground snow load. Colville pairs its 30-inch frost line with a 40 psf roof snow load. Our Spokane County snow load guide explains how to look up your parcel's number.

How Raven handles it

• We look up your jurisdiction first: city limits, County, or a neighboring county change the numbers
• Footings go below the local frost line: for every steel building, pole building and foundation we pour
• One crew for the building and the concrete: so the footing depth, anchor bolts and slab all match the engineering

We pour across Spokane County and north into Stevens and Pend Oreille counties, including our Deer Park, Colville and Newport concrete crews' service areas.

Get a free quote

Planning a shop, foundation or slab? Call 509-350-2016 or request a free quote with your address and project size, and we'll tell you the frost depth and snow load your site is designed for. See our concrete flatwork services.

Sources

• City of Spokane, SMC 17F.040.105 (design criteria)
• City of Spokane / Spokane County Joint Policy BUILD-07, Official Frost Depth
• Spokane County BP-06 Residential Building Permits (design criteria)
• City of Spokane Valley SVMC 24.40
• City of Liberty Lake, Construction Design Criteria
• City of Airway Heights, Geographic Design Criteria
• City of Deer Park Municipal Code 15.04, Building Codes
• City of Colville, Building FAQs (design criteria)
• Stevens County Building Code Ordinance 02-1984 (frost depth)
• Pend Oreille County Geographic Design Criteria
• Spokane County BP-32, Pole Buildings
• IRC frost protection requirements, R403.1.4 and R403.1.4.1 (summary)