November 4, 2026steel buildings

Can a Barndominium Have a Basement in Spokane County? Slab vs. Crawlspace vs. Basement (2026)

Short answer: yes, a barndominium can have a basement in Spokane County. A barndo is a building type, not a foundation type, so a steel-frame (PEMB) or post-frame barndo can sit on a slab, a stem wall with a crawlspace, or a full basement. The catch is that a basement changes almost everything below the frame: the engineering, the excavation, egress windows, drainage, waterproofing and insulation. Here's how the three options compare, what Washington's codes require for each, and how the steel or post frame ties into the concrete.

What is a barndominium made of?

A barndominium ("barndo") is a metal pole barn, post-frame or barn-like building with sheet metal siding that has been partly or fully finished as a home, according to Wikipedia's summary of the term. Today the name is used loosely, whatever the frame. The two common structures:

Steel frame (PEMB, "red iron"): steel columns and rafters engineered by the building manufacturer, bolted to anchor rods cast into a concrete foundation, with steel purlins, girts and metal panels
Post-frame (pole barn style): wood posts with trusses on top. The National Frame Building Association (NFBA) defines post-frame posts as either embedded in the soil on footings or attached to a concrete foundation
The living space inside: framed walls, insulation and finishes like any house. Once it's a dwelling, the Washington residential code and energy code apply the same way they do to a stick-built home

The three foundation options

Slab-on-grade

The most common barndo foundation: a concrete floor that sits on the ground, with thickened, deeper footings at the perimeter and under columns.

Minimum slab: Washington's residential code (IRC R506.1) sets a minimum of 3.5 inches for a concrete floor slab. Barndo slabs that also carry a shop, vehicles or column loads are designed thicker where the engineer calls for it. See our shop slab thickness guide
Vapor retarder: for heated living space, IRC R506.2.3 requires a minimum 10-mil vapor retarder meeting ASTM E1745 Class A, with joints lapped at least 6 inches. Unheated garages, utility buildings and accessory structures are exempt. Our vapor barrier guide covers the details
Slab-edge insulation: the Washington State Energy Code (Table R402.1.3) lists R-10 slab insulation to a depth of 4 feet for Washington's climate zones. Insulation that extends away from the building must be protected by pavement or at least 10 inches of soil (R402.2.9)
Radiant floors: if the slab is heated, R402.2.9.1 requires the entire heated slab to be isolated from the soil with at least R-10 insulation, under every compliance path
Best for: the simplest build, single-level living, and a shop side where you'll drive in

Stem wall with a crawlspace

A continuous concrete foundation wall on a footing, with a wood or engineered floor framed over a crawlspace.

Ventilation: IRC R408.2 requires at least 1 sq ft of vent opening for every 300 sq ft of under-floor area, unless it's built as an unvented crawlspace under R408.3, which requires a sealed Class I vapor retarder, a radon system and mechanical ventilation or conditioning
Ground cover: Washington's R408.1 calls for 6-mil black polyethylene (or approved equal) over the crawlspace ground, lapped at least 6 inches and run to the foundation wall
Floor insulation: the energy code table lists R-30 for floors over unconditioned space
Best for: sloped lots, a raised floor for plumbing access, or matching a traditional house look. For a barndo with a shop bay, the shop side usually stays slab-on-grade

Full basement

Concrete basement walls on footings, with the barndo's main floor framed over the top and a slab at the bottom.

Insulation: the energy code lists below-grade walls at R-10 continuous on the exterior, R-15 continuous on the interior, or R-21 cavity insulation plus an R-5 thermal break between the slab and the wall
Slab: the basement floor gets the same 10-mil Class A vapor retarder as any other heated slab
Best for: more finished space on the same footprint, storage, mechanical rooms, or a walkout on a sloped lot

How a steel (PEMB) frame changes the foundation

A pre-engineered metal building isn't just a slab with bolts in it. The manufacturer engineers the steel and gives you the loads; your foundation engineer designs the concrete.

What the manufacturer provides: Ceco Building Systems' published specifications, for example, say anchor rod setting plans include column reactions for use in designing the foundation, but the manufacturer is not responsible for the design or adequacy of the foundation. Anchor rods and other embedded items are excluded from the building package
What the reactions mean: each main frame column pushes down (building weight plus snow), can pull up (wind uplift on a light steel building), and pushes outward at the base (horizontal thrust from a gable rigid frame), as Universal Steel's foundation guide explains
How thrust is handled: typically with tie rods between opposite column foundations, or with hairpins, U-shaped bars at each column that pass the force into the slab reinforcement. That makes the slab part of the structure, so later saw cuts or trenches near columns should go past the engineer first
Anchor rod embedment: per the MBMA practices cited by Universal Steel, the manufacturer's anchor rod plan shows only location, diameter and projection. Embedment depth is the foundation engineer's call
With a basement: ask your engineer early how the column loads, uplift and thrust get into the basement walls and footings, since the slab-based tie options change when there's a basement under part of the floor

Raven isn't tied to one metal building manufacturer. We source each building from whichever manufacturer can deliver the engineered package fastest, then pour the foundation to that manufacturer's anchor rod plan and your engineer's design.

How a post-frame barndo works with a basement

Yes, it can be done: NFBA's post-frame foundation guide says a post-frame building can be placed on a basement wall designed for post point loads, using the same wet-set or drill-set brackets used on frost walls and piers
Partial basements: NFBA also notes a partial basement or storm shelter can be inset inside a building that otherwise uses ground-embedded posts or concrete piers
Brackets carry real loads: Perma-Column's Sturdi-Wall design guide says its standard brackets transfer uplift, shear and downward forces into the concrete, but don't transfer meaningful moment, so the building still has to be designed to resist lateral loads
Permits: Spokane County's residential submittal table lists structural engineering where applicable, and specifically notes that includes pole buildings

Comparing the two frames? See our red iron vs. pole barn guide.

Frost depth: how deep the footings go

Every option needs footings below the local frost line (IRC R403.1.4.1), unless it's built as a frost-protected shallow foundation or on solid rock. Around Eastern Washington:

Spokane and unincorporated Spokane County: 24 inches below finished grade, under the City/County joint policy BUILD-07 and the County's design criteria. BUILD-07 says it can't be less than 24 inches
City of Deer Park: 36 inches, per the City's adopted design criteria
Stevens County: 30 inches below finish grade for footings exposed to outside temperatures
Pend Oreille County: 30 inches below finish grade, measured from the bottom of the footing

A basement's footings end up far below frost depth anyway. Slabs and crawlspaces are where the frost line really sets the depth. Our frost depth guide explains why it matters.

Basement rules: egress, drainage and waterproofing

Egress windows (IRC R310)

Where required: basements, habitable attics and every sleeping room need at least one operable emergency escape and rescue opening. If a basement has bedrooms, each bedroom needs one. Spokane County's building FAQ says the same for basements in dwelling units
Size: at least 5.7 sq ft net clear opening (5 sq ft at grade floor), at least 24 inches high and 20 inches wide
Sill height: the bottom of the opening can be no more than 44 inches above the floor
Window wells: below grade, the well must be at least 9 sq ft with at least 36 inches of width and projection. Wells deeper than 44 inches need a permanently attached ladder or steps

Foundation drainage (IRC R405)

When required: drains are required around concrete or masonry foundations that retain earth and enclose habitable or usable space below grade
Details: gravel or crushed stone drains extend at least 1 foot beyond the footing and 6 inches above its top, covered with a filter membrane. Perforated pipe sits on at least 2 inches of washed gravel and is covered with at least 6 inches
The soil exception: a drain isn't required on well-drained ground or sand-gravel soils classified as Group I in Table R405.1 (gravels and sands with little or no fines). Your soils, not your neighbor's, decide this, and we recommend drainage on any finished basement

Dampproofing vs. waterproofing (IRC R406)

Dampproofing: required on basement walls that retain earth, from finished grade down to the top of the footing (or 6 inches below the top of the basement floor, whichever is higher)
Waterproofing: required instead where a high water table or other severe soil-water conditions are known to exist. Approved systems include 40-mil polymer-modified asphalt and 60-mil flexible polymer cement, among others

Radon

Spokane County's building FAQ says the County is one of six in Washington requiring radon mitigation measures in newly constructed homes and additions. A barndo is no exception, and a basement or slab is where that system goes.

Permits in Spokane County

Codes in effect: unincorporated Spokane County enforces the 2021 International Residential Code, the 2021 International Building Code and the Washington State Energy Code
Plans: the County's residential permit guide (BP-06) asks for a foundation plan, floor plan, cross sections and energy compliance forms. For basements, the foundation plan has to show beams, joists, footings and posts. For crawlspaces, it has to show the crawlspace access and vents
Engineering: BP-06 lists structural engineering as applicable, including pole buildings. A PEMB comes with manufacturer engineering for the steel, and the foundation is designed to the column reactions
Permit life: County building permits expire 3 years after issuance. The Director may grant one extension of up to 180 days if you request it in writing before the permit expires, per the County's building FAQ

Which foundation fits your barndo?

Slab-on-grade: simplest and the natural fit for a shop bay. Plan R-10 edge insulation and a Class A vapor retarder on the living side
Crawlspace: a raised floor and plumbing access, with vents (or an unvented R408.3 design), ground cover and R-30 floor insulation
Basement: the most space per footprint, plus egress, drainage, damp or waterproofing, R-10/15/21 wall insulation and engineering to carry the frame's loads
Mix and match: a slab under the shop and a basement or crawlspace under the living side is common. The engineer just has to design the transition

What it costs

Raven's going rate for an installed pre-engineered metal building is about $60 to $75 per sq ft, and installed pole buildings run about the same. That's the building, and electrical, plumbing and utility hookups are not included and are extra. Foundations, basements and finished barndominium interiors are quoted per project, because excavation, soils, engineering and finishes vary so much from site to site. See our metal building kit vs. installed guide, our snow load guide and our metal building insulation guide.

Get a barndominium quote

Call 509-350-2016 or request a free quote with your building size, location and whether you want a slab, crawlspace or basement. See our steel building services and pole building services.

Sources

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