How to Prep a Site for a Pole Barn or Metal Building in Spokane (2026 Guide)

Short answer: good site prep for a pole barn or metal building in Spokane County means locating utilities through 811 at least two full business days before digging, stripping topsoil and vegetation, building a level pad of compacted fill and gravel, and grading the ground to fall away from the building at 5 percent for the first 10 feet. A grading permit is often not needed when the dirt work is part of a permitted building, but it can be once you move more than about 50 cubic yards, grade a driveway across a drainage, or start before the building permit is issued. Here's what the rules say and how we prep a site before a slab, footing or post goes in.

Why site prep matters more than the building

A steel frame or a post-frame building is only as good as the ground under it. Soft fill settles, slabs crack, doors stop lining up and water ends up inside. Most of that is decided before any concrete is poured or any steel shows up:

• Bearing: footings and slabs need undisturbed native soil or properly compacted fill, not loose spoils from the excavation
• Drainage: a pad that sits lower than the ground around it collects snowmelt every spring
• Frost: footings and posts have to reach frost depth, which is 24 inches in the City of Spokane and unincorporated Spokane County under the joint frost-depth policy. Some nearby towns set it deeper, so we check the address. See our frost depth guide

Step 1: Call 811 before anyone digs

Washington's dig law, RCW 19.122, applies to anyone moving earth, including a homeowner with a rented mini excavator.

• Mark the area first: outline the excavation boundary on the ground in white paint or white flags
• Give notice on time: contact 811 (or the online locator) at least two full business days and no more than 10 full business days before the work-to-begin date. The day you call, weekends and legal holidays don't count
• Wait for every answer: since January 1, 2026, an excavator can't start digging until every utility operator in the area has given a positive response, including for lines they can't locate
• Keep the marks: marks are good for 45 days or until the project ends, whichever comes first, so a long project needs a new locate
• Private lines aren't marked: 811 covers utility-owned lines. Your own well line, septic, buried power to an outbuilding or irrigation won't be marked, so tell us where they are

Step 2: Find out if you need a grading permit

In unincorporated Spokane County, grading permits come from Spokane County Code 3.10. The code says no grading without a permit, then lists exemptions. The ones that matter for most shop sites:

• Footings and basements: excavation below finished grade for footings, basements or retaining walls covered by a valid building permit is exempt. That exemption doesn't cover fill made with the dug-out material, or a cut taller than 5 feet left unsupported
• Shallow cuts: an excavation less than 2 feet deep, or one that doesn't create a cut slope over 5 feet high and steeper than 1.5 horizontal to 1 vertical
• Small fills: fill less than 1 foot deep on ground flatter than 5 to 1, or less than 3 feet deep, that isn't meant to support a structure, stays under 50 cubic yards per lot and doesn't block a drainage course
• Big jobs: grading over 5,000 cubic yards is "engineered grading" and needs a plan from a civil engineer

The County's grading brochure (BP-46a) adds that a separate grading permit is needed if you want the site graded before the building permit is approved, and that driveways moving around 50 cubic yards, crossing other parcels or crossing drainage ways may need one too. Sites near wetlands, shorelines or other critical areas can need a permit for any fill. Cities like Spokane, Spokane Valley and Liberty Lake have their own grading rules, so we check with the right office for your address.

Exempt or not, the work still has to meet the County's erosion and sediment control rules (its BP-19 brochures cover them), so we plan silt fence or wattles and a rock construction entrance wherever runoff could leave the site.

Step 3: Strip, then build the pad

The building code is specific about what goes under a slab:

• Strip it: all vegetation, topsoil and foreign material comes out of the building area (IRC R506.2). Topsoil is organic, compresses over time and should never end up under concrete
• Limit loose fill: fill under a slab has to be free of vegetation and debris and compacted for uniform support. Unless approved otherwise, fill depth is capped at 24 inches for clean sand or gravel and 8 inches for earth (IRC R506.2.1)
• Add a base: a 4-inch base of clean graded sand, gravel or crushed stone passing a 2-inch sieve goes under below-grade slabs, unless the slab sits on well-drained Group I sand and gravel soils (IRC R506.2.2)
• Compact in lifts: we place fill in thin lifts and compact each one with a plate compactor or roller instead of dumping it all and running over it once

For commercial and larger buildings designed under the IBC, the bar is set by test, not by eye. Under IBC 1804.6, where shallow foundations bear on compacted fill, the fill has to follow an approved geotechnical report. The exception is fill 12 inches deep or less, which needs no report if it reaches at least 90 percent of maximum dry density by ASTM D1557 (the Modified Proctor test), verified by special inspection. Deeper fill needs a geotechnical investigation that sets the lift thickness, test method and required density.

Step 4: Grade so water leaves

Spokane gets its water as snow, and it all melts at once in late winter, often over still-frozen ground. Grading is what keeps that melt out of your shop:

• Homes and residential buildings: the ground must fall at least 6 inches in the first 10 feet away from the foundation. Where a lot line or slope prevents that, swales or drains have to carry water away (IRC R401.3)
• Paved areas next to the building: driveways, aprons and walks within 10 feet of the foundation slope at least 2 percent away (IRC R401.3)
• Commercial buildings: IBC 1804.4 calls for a 5 percent slope away for at least 10 feet, with swales sloped at least 2 percent
• Set the floor high: we set the finished floor above the surrounding grade so the slab edge isn't a dam. On a metal building, roof runoff also comes off in sheets at the eave, so plan where that water goes before the gutters or drip line are built

Pole barn vs. metal building: what's different

• Pole buildings: posts are set in holes, so the pad mostly needs to be level, well drained and stripped of topsoil inside the walls. Many owners start with a compacted gravel floor and pour a slab later. Post depth and backfill have their own rules, covered in our pole barn post depth guide
• PEMB (red iron) buildings: the columns sit on engineered footings with anchor bolts, and the slab often ties in. The pad has to be close to final grade and compacted before forms go in. See PEMB anchor bolts
• Heated shops and barndominiums: add a vapor retarder under the slab. See vapor barriers under slabs

What it costs

Raven's current installed price for a PEMB metal building or a pole building is about $60 to $75 per square foot. Electrical, plumbing and utility hookups are extra. Site prep depends heavily on your ground, how much cut and fill it needs and how far material has to be hauled, so we price dirt work after we've walked the site.

Get a site prep and building quote

Raven Buildings does the dirt work, the concrete and the building with our own crews, so the pad is built for the foundation that goes on it. Because we aren't tied to one manufacturer, we source PEMB packages from whoever has the fastest delivery. Call 509-350-2016 or request a free quote with your address or parcel number, building size and intended use.

Sources

• PEMB and pole building pricing: Raven Buildings' current rates
• Washington UTC, Dig Law
• RCW 19.122.030, Excavator and facility operator duties before excavation
• WA 811, Homeowners
• Spokane County Code Chapter 3.10 (grading permits and exemptions), Municode
• Spokane County BP-46a, Typical Grading Permits (PDF)
• Spokane County BP-25, Permit Exemptions (PDF)
• City of Spokane / Spokane County Joint Policy BUILD-07, Official Frost Depth (PDF)
• IRC R506, Concrete Floors (On Ground) (UpCodes)
• IBC 1804.6, Compacted Fill Material (UpCodes)
• IBC 1804.4, Site Grading (UpCodes)
• ICC, Residential Code Essentials sample: IRC R401.3 drainage (PDF)