Updated
A shipping container is built to be carried on its corners. Stacked on a ship or hanging from a terminal crane, its load runs down the four corner posts into the bottom corner castings. A foundation that respects that — four firm, level, dry bearing points — is cheap and lasts for decades. One that ignores it, by laying the box flat on soil or on a surface that holds water, is how containers rust through from underneath and end up with doors that will not shut.
This guide covers the options from temporary to permanent, shows how to work out the load on each corner from the container's own figures, and says where a structural engineer should take over.
Why the corners carry the load
The walls, roof and floor of a container are panels. The strength is in the frame: four corner posts, top and bottom side rails, end rails and eight ISO 1161 corner castings. The floor cross-members pass their load to the bottom side rails, and the rails pass it to the bottom corner castings. Support those four points properly and the structure works as it was designed to.
Each bottom casting has a footprint of about 178 × 162 mm — roughly 0.03 m². That small area is why a container set straight onto a lawn or a gravel drive sinks at one corner first: even an empty 20ft puts around 190 kN/m² through each casting, and a loaded one many times that. A pad under each corner spreads the load over enough ground to carry it.
Foundation types, from temporary to permanent
- Concrete pads (pier foundations) — one pad under each corner casting, cast in place or precast and bedded on compacted ground. The standard answer for a container that is staying: little concrete, free airflow underneath, and easy to level accurately.
- Strip footings — two concrete strips running across the width of the container, one under each end, carrying both castings on that end. More concrete than pads, but simpler to set out accurately, and a good choice where several containers stand side by side on shared strips.
- Concrete slab — a full slab under the footprint. Worth it only if you need a hard standing anyway, such as a yard or a workshop apron. Even then, set the container on steel plates or pads under the corners rather than flat on the concrete, and give the slab a fall so water runs away instead of pooling under the floor.
- Compacted gravel bed — crushed stone compacted in layers, with pads or sleepers under the corners on top. It drains well and suits semi-permanent placement. The gravel on its own is not a bearing point: a casting pushes into it unevenly.
- Sleepers, paving slabs and kerbs — for temporary placement on firm ground: concrete sleepers, heavy concrete slabs or timber beams under each corner. Use new timber or concrete. Old tar-oil (creosote) treated railway sleepers are subject to chemicals-law restrictions and may not be used in gardens or anywhere people frequently touch them.
Working out the load on each corner
You do not need a rule of thumb for this. Take the mass the container will actually have — its tare plus what you put in it — divide by four and convert to force: load per corner (kN) ≈ total mass (kg) ÷ 4 × 9.81 ÷ 1 000. Divide that by the area of the pad and you have the pressure the ground must carry.
The tare and maximum gross figures below are the nominal values used throughout this site; the individual unit's CSC plate governs. Maximum gross is the absolute upper bound. A storage container rarely gets near it, but a store full of steel stock, paper or tiles gets closer than people expect. See container weight.
- 10ft, empty (tare about 1 300 kg): about 3.2 kN per corner. At its 10 160 kg maximum gross: about 24.9 kN.
- 20ft, empty (tare about 2 250 kg): about 5.5 kN per corner. With 5 t of contents (7 250 kg in total): about 17.8 kN. At 30 480 kg maximum gross: about 74.8 kN.
- 40ft, empty (tare about 3 750 kg): about 9.2 kN per corner. With 10 t of contents: about 33.7 kN. At 30 480 kg maximum gross: about 74.8 kN.
A worked example: a 20ft with 5 t of contents on four 50 × 50 cm pads (0.25 m² each) puts about 17.8 ÷ 0.25 ≈ 71 kN/m² into the ground under each pad, plus the weight of the pad itself. The same container at maximum gross on the same pads: about 299 kN/m². Standing directly on its castings it would be about 2 600 kN/m².
Whether 71 or 299 kN/m² is acceptable depends on the ground, and that figure has to come from someone who has looked at it. Topsoil, made ground and recently backfilled trenches are the usual problems; undisturbed, well-drained natural ground is normally far better. We deliberately do not publish soil values here, because a number that is right for one plot can be dangerous on the next.
When to bring in an engineer
For a container standing temporarily on firm, dry ground with light contents, pads or sleepers are ordinary practice. Get a structural engineer or a ground investigation when any of these apply:
- The container is permanent, or is part of a building application
- The contents are heavy: machinery, steel, stone, paper stock, fully loaded racking
- Containers will be stacked or joined, or openings will be cut into the walls
- The ground is soft, filled, sloping, or close to an excavation or retaining wall
- The container is to be anchored to its foundation against theft or wind
Permanent concrete foundations in Germany must be taken below frost depth: DIN 1054 sets a minimum of 0.80 m for frost-free foundations, and regional practice can require more. Shallow pads that are not frost-free can lift in a hard winter — acceptable under a temporary container you can re-level, not under a permanent one.
Level, tolerance and the doors
A container is square only when its four corners lie in one plane. Set one corner low and the frame twists. The first sign is locking bars that will not drop into their keepers, or one door leaf standing proud of the other. Level all four bearing points to within a few millimetres of each other, and check across the diagonals with a laser, a levelling instrument or a water level, not only along the sides.
Check again after the first winter and after heavy rain. Pads on new ground settle, and a few millimetres of steel packing under one corner is far cheaper than a door that has to be forced.
To correct a corner, lift it at the corner casting with a jack rated for the load and pack under the casting with steel plates. Never jack on the side rails mid-span or on the floor, and never reach under a raised container.
Drainage and air under the floor
The underside is where a container dies. Cross-members and the plywood floor stay sound for decades if they can dry out, and fail within a few years if they sit in wet ground. Pads lift the base clear so air moves underneath. Keep that gap open: no soil, grass or leaves built up against the bottom rails.
Never place a container in a hollow or anywhere surface water collects. On a slab or paving, make sure water runs away from the footprint. A layer of compacted gravel under and around the pads keeps vegetation down and the ground draining.
The air gap matters for the inside too. A box on cold, damp ground has a cold, damp floor, which feeds condensation — see condensation and insulation.
Before the delivery arrives
The pads must be in place, cured and level before the lorry arrives, and their spacing must match the container. The castings sit at the extreme corners, so set out from the external dimensions: 6 058 × 2 438 mm for a 20ft, 12 192 × 2 438 mm for a 40ft, 2 991 × 2 438 mm for a 10ft. Make the pads a little larger than the castings so the driver has some tolerance when placing.
Match the pads to the delivery method. A crane truck sets the container straight down and places it most accurately; a tilt-bed slides it off the back, so ask whether raised pads suit the vehicle before you build them. Container delivery and container unloading cover access and what must be ready on the day.
A foundation does not decide whether you need permission. Under the German model building code, a structure also counts as connected to the ground when it simply rests there under its own weight. See container planning permission in Germany.