Technical Resource

    Shipping Container Foundation and Site Preparation

    A container is only as durable as what sits underneath it. This is how US buyers prepare ground, gravel pads, concrete foundations and drainage so the unit stays level, dry and serviceable for 20+ years.

    Ground Preparation

    Start with the dirt underneath

    Strip 4–6 inches of topsoil, organic matter and grass from the footprint plus a 2 ft margin on every side. Topsoil holds moisture, compresses under load and harbors the biological activity that rots the underside of a container. Below it you want firm subsoil, clay, silty loam or compacted glacial till are all fine. Sandy soil drains best but compacts least; add geotextile fabric before backfilling.

    After stripping, compact the exposed subsoil with a plate compactor in two passes. If the site is in a freeze zone (most of the US north of I-40), extend excavation 6 inches below your local frost depth and backfill with compacted aggregate to prevent frost heave from torquing the corner castings.

    Lay a non-woven geotextile (Mirafi 140N or equivalent) across the prepared subgrade before any aggregate goes down. It costs $0.30/sq ft and triples the working life of the gravel by preventing the base from pumping mud upward over time.

    Gravel Foundations

    The default US foundation

    A compacted crushed-stone pad is the right answer for 90% of buyers. It drains, it adjusts to ground movement, it costs a fraction of concrete, and it is reversible if you move the container later.

    Material

    ¾-inch minus crushed stone (AB-3, Class 5, Item 4, names vary by region). Avoid pea gravel and washed stone; they will not lock together under load.

    Depth

    6 inches minimum, 8 inches in wet or frost-prone climates. Compact in 2-inch lifts with a vibratory plate compactor, not by tamping the full depth at once.

    Footprint

    Container length + 4 ft × container width + 4 ft. The 2 ft margin keeps rainwater from undercutting the pad edges at the corner castings.

    Volume math: a 20ft container at 6 inches deep needs ~5.2 cubic yards. A 40ft container needs ~9.8 cubic yards. Order 15% more than the calculation to account for compaction and edge spillage.

    Concrete Foundations

    When permanence justifies the cost

    Concrete piers (4 corners)

    24″×24″×24″ poured-in-place piers at each corner casting, set on a 12-inch gravel base below frost line. The container bridges air between piers, best ventilation for the underside.

    $800–$1,800 installed

    Concrete strips

    Two continuous strips under each long rail, 12-inch wide, 8-inch deep. Distributes load on softer ground than piers and offers better stability for stacking or modifications.

    $1,500–$3,200 installed

    Full slab

    Continuous 5–6 inch reinforced slab covering the entire footprint. Required for some county permits and for any container that will be converted into occupied space.

    $3,500–$7,000 installed

    A full slab traps moisture against the container floor cross-members and accelerates underside corrosion unless you add a 2-inch air gap on neoprene pads. For pure storage, piers or strips outperform a slab on every metric except permit compliance.

    Drainage

    Water is the only thing that kills a container

    Surface drainage

    Pitch the pad at 1–2% (about ¼ inch per foot) away from the container in the direction that gets the unit on slightly higher ground. If the lot slopes toward the container, cut a swale 6 ft uphill or install a French drain at the high side.

    Roof runoff

    A 40ft container roof sheds about 320 gallons per inch of rain. Without gutters, that water lands at the base and erodes the gravel pad on one side. Add cheap aluminum gutter (~$120 in materials) to direct it away.

    Underneath ventilation

    Set the container with a 4–6 inch air gap to the ground (concrete piers do this automatically; a gravel pad needs 4×4 pressure-treated runners or 4-inch concrete blocks under the castings). Stagnant air under a sitting container condenses overnight moisture into the cross-members.

    Freeze-thaw exposure

    Standing water that freezes between the pad and the corner casting expands and shifts the container off-level by spring. In freeze zones, the gravel pad must extend below frost depth or sit on concrete piers that do.

    Access Requirements

    Where to place the container

    The pad has to be reachable by a tilt-bed truck or crane on delivery day. The most beautiful prepared site is worthless if the truck cannot get within 30 ft of it. Plan placement around four constraints simultaneously:

    • Delivery path: 12 ft wide, 14 ft tall, 100 ft of straight pull-back behind the truck for a 40ft tilt-bed. See our delivery guide for full specs.
    • Door orientation: doors face the tilt direction by default. Decide before delivery whether you want doors toward the building or away.
    • Setback & sight lines: check property line setbacks (typically 5–10 ft minimum), HOA visibility rules, easements and overhead utility right-of-ways before you commit.
    • Future moves: if you might relocate the container, avoid pads that get boxed in by future construction. Gravel pads stay accessible; full slabs do not.

    Mistakes to Avoid

    The eight site-prep errors we see most often

    Skipping the topsoil strip

    Organic matter under the pad decomposes and the container sinks unevenly within 18 months.

    Using pea gravel or washed stone

    Round-edge stone does not interlock; the pad shifts under load and the container goes out of level.

    No geotextile fabric

    Without it, fines migrate up through the gravel and the pad reverts to mud within 2–3 seasons.

    Setting the container directly on dirt

    Cross-members trap moisture, underside corrodes 3× faster, doors jam within 5 years.

    Forgetting the air gap

    No ventilation under the floor = condensation on the cross-members year-round.

    Wrong-direction slope

    Pad slopes toward the container, water pools at the door sill and rots out the door header gasket first.

    Pad too small

    No 2 ft margin means runoff undercuts the corner castings and the container shifts.

    Ignoring frost depth

    Pad freezes and heaves, twisting the container off-level by spring.

    FAQ

    Frequently asked questions

    Technically a container can sit on dirt and stay functional. In practice, bare ground traps moisture against the cross-members, accelerates underside corrosion, and lets the corner castings sink unevenly, which jams the doors. Even a basic 6-inch gravel pad more than doubles the structural lifespan.

    Four concrete piers under the corner castings is the gold standard for permanent installations. A 6-8 inch compacted gravel pad is the best price-to-performance choice for 90% of US buyers. Full slab is overkill unless you are building a structure on top, but is required for some county permits.

    For a 6-inch compacted pad sized 12 ft × 44 ft (2 ft margin all around), you need approximately 9.8 cubic yards of crushed stone (¾-inch minus or AB-3 base). Budget 11 yards to account for compaction loss and edges.

    Yes, within ½ inch corner-to-corner. An out-of-level container twists, which means doors that won't latch, gaskets that don't seal, and accelerated wear at the corner welds. Use shims under the castings, not under the cross-members.

    Build the pad with a 1–2% slope away from the container footprint to prevent water pooling at the cross-members. If your natural grade slopes toward the container, dig a shallow swale uphill to divert runoff.

    Depends on the county and zoning. Many rural and industrial-zoned parcels need none. Residential and some commercial zones require a permit for any structure over 120 sq ft, a 20ft container is 160 sq ft. Always check before delivery; some jurisdictions also restrict visibility from the street.

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    Site ready? Let's get your container quoted.

    We sell new One Trip and used Cargo Worthy containers from US depots nationwide. Tell us your zip code and intended use, we will quote unit, delivery and crane (if needed) in one number.

    Related: Delivery Guide · CW vs WWT · Container Buying Guide