Commercial vs. Residential Concrete in Spokane: Mix Strength, Special Inspection and ADA Slopes (2026)

Short answer: "commercial concrete" isn't a different material. It's the same cement, rock and water held to a different set of rules. A homeowner's driveway falls under the residential code. A shop floor for a business, a parking lot, a storefront sidewalk or a warehouse slab falls under the commercial building code, ADA accessibility rules, and often an engineer's specs and a special inspector. Here's what actually changes when a Spokane-area project crosses that line.

Which code applies

• Houses, duplexes, townhouses and their garages: the International Residential Code (IRC), as adopted and amended in Washington
• Everything else: businesses, shops used for work, warehouses, churches, apartment buildings and parking lots for those buildings fall under the International Building Code (IBC), as adopted by Washington's State Building Code Council
• Accessibility: Washington adopts IBC Chapter 11 and ICC A117.1 for barrier-free access, and state law says local governments can't amend those requirements. Federal ADA standards apply to public accommodations too
• Public right-of-way: a sidewalk, curb or approach in the street is built to the city's own standard plans, whether the property is a house or a business

Strength and durability: the exposure classes

Residential concrete strength in Washington comes from IRC Table R402.2, which keys strength to weathering. Spokane-area garage floors, porches and exposed steps need at least 3,500 psi, air-entrained. Our concrete PSI guide covers those numbers.

Commercial structural concrete is usually specified under ACI 318, which assigns each member an exposure class for freezing and thawing:

• F0, no freeze-thaw exposure: no maximum water-to-cement ratio, 2,500 psi minimum
• F1, freeze-thaw with limited water: 0.55 maximum water-to-cementitious ratio, 3,500 psi minimum
• F2, freeze-thaw with frequent exposure to water: 0.45 maximum, 4,500 psi minimum
• F3, freeze-thaw with water and deicing chemicals: 0.40 maximum, 5,000 psi minimum for reinforced concrete. ACI's commentary uses parking structure decks and above-grade foundation walls that collect snow and deicers as examples
• Air entrainment: F1, F2 and F3 all require air-entrained concrete, at levels set by aggregate size
• When in doubt: NRMCA's guide to selecting exposure classes says if it's unclear whether F1 or F2 applies, choose the more conservative F2

In practice, that means a commercial entry slab or loading apron in Spokane that sees snowmelt and deicers is often specified well above what a homeowner's patio needs. The engineer or architect on the project sets the class; we order the mix to match and don't add water on site.

Special inspection: who checks the concrete

On commercial work, the IBC requires special inspection and testing of concrete construction under Section 1705.3: a third-party inspector verifies rebar placement, anchors cast in concrete, mix and placement, and samples the concrete for strength tests. The code exempts some common work:

• Isolated spread footings of buildings three stories or less, fully supported on earth or rock
• Continuous footings for walls of buildings three stories or less that support light-frame walls, follow the code's prescriptive footing table, or are designed at 2,500 psi or less
• Nonstructural slabs on grade, meaning slabs supported directly on the ground that aren't part of the structural system
• Concrete foundation walls built to the code's prescriptive table
• Concrete patios, driveways and sidewalks on grade

Whether a given footing or slab is exempt is the building official's and engineer's call. What it means for you: on a commercial job, inspection visits and test cylinders are part of the schedule, so the pour date has to line up with the inspector, not just the ready-mix plant.

Accessibility: slopes measured in fractions of an inch

This is where commercial flatwork differs most from a residential driveway. Under the 2010 ADA Standards:

• Walking surfaces: running slope no steeper than 1:20 (5 percent) and cross slope no steeper than 1:48 (about 2 percent)
• Ramps: running slope no steeper than 1:12
• Accessible parking spaces and access aisles: essentially level, with slopes no steeper than 1:48 in any direction. Access aisles must be at least 60 inches wide and at the same level as the spaces they serve
• Van spaces: 98 inches of vertical clearance along the van route

The City of Spokane's sidewalk standard is even tighter on cross slope: its standard plans call for a 1.2 percent minimum and 2.0 percent maximum cross slope, with no extra construction tolerance. That leaves very little room. On a commercial site we set grades with a laser and check slopes before the concrete sets, because grinding or replacing a noncompliant ramp costs far more than forming it right.

Work in the street: approaches and sidewalks

In the City of Spokane, a driveway approach or sidewalk in the right-of-way:

• Needs city approval first: driveway approach applications require a site plan showing existing conditions and proposed changes, and the City says review can take up to five working days
• Has size limits: approaches are limited to a maximum of 40 percent of street frontage, up to 30 feet
• Must be built by a qualified contractor: construction has to be performed by a contractor who has met the City's requirements to work in the right-of-way, with a Street Obstruction Permit obtained before any work starts
• Is built to standard plans: sidewalks to Standard Plan F-102, approaches to the F-103 and F-104 series, curb ramps to the F-105 series, and the work is inspected

Commercial building permits can also trigger frontage improvements such as sidewalks, curbs and street trees under Spokane's street improvement rules, so it pays to know early whether your project will include them.

Commercial vs. residential at a glance

• Code: IRC for homes; IBC plus accessibility rules for commercial
• Mix: IRC Table R402.2 by weathering for homes; ACI 318 exposure classes, often 4,500 to 5,000 psi where deicers and water meet freeze-thaw, for commercial
• Inspection: city or county building inspections for homes; commercial work adds special inspection and strength testing unless exempt
• Grades: drainage-driven on a driveway; ADA slopes on commercial walks, ramps and accessible parking
• Paperwork: commercial projects usually come with stamped drawings, specs and submittals the contractor has to follow

Where Raven fits

Raven Buildings pours footings, slabs and flatwork for shops, metal buildings and commercial sites across Spokane County and Eastern Washington, and erects the pre-engineered metal buildings that sit on them. We're not tied to one building manufacturer, so we source each steel package from whoever can deliver fastest. Concrete costs on commercial work depend on the specs, inspections and site, so we price each project from the drawings rather than a per-foot figure.

• Concrete services: see our concrete flatwork services and steel building services
• Metal building foundations: our PEMB foundation guide
• Slab layout: our control joint spacing guide

Get a commercial concrete quote

Call 509-350-2016 or request a free quote. Send your drawings or a site plan, and we'll walk through the specs, inspection requirements and schedule with you.

Sources

• 2021 Washington Residential Code, Chapter 4 Foundations (Table R402.2)
• Washington State Building Code Council: 2021 IBC with Washington amendments (PDF)
• IBC Section 1705.3, Concrete Construction special inspection (UpCodes)
• NRMCA / ACI: Selecting Exposure Classes and Requirements for Concrete (PDF)
• U.S. Access Board: ADA Standards Chapter 4, Accessible Routes
• U.S. Access Board: Chapter 5, Parking Spaces
• City of Spokane Standard Plans, Section F, Curbs and Sidewalks (PDF)
• City of Spokane Driveway Approach Application (PDF)
• Spokane Municipal Code 17H.010.040, Street Improvement Projects