Groundwork decides how a container behaves for the next twenty years, and the question we are asked most is gravel pad vs concrete slab. Concrete piers are the forgotten third option, and on many sites they win.
One fact drives it all. A container carries its whole load through four corner castings specified in ISO 1161, each roughly 178 by 162 mm. An empty 20ft weighs about 2,200 kg and a 40ft about 3,800 kg, while a loaded 20ft can reach a maximum gross of 30,480 kg. Support those four points and the unit stays square. Miss them and the doors bind at roughly 10 to 25 mm out of level.
What is a gravel pad and how is it built?
A gravel pad is 150 to 300 mm of compacted crushed stone over a geotextile, built wider than the container and draining away on all sides.
The build up matters more than the depth. We strip topsoil to firm subsoil, lay a geotextile separator so the stone cannot pump into the ground, then fill with angular crushed stone in layers of 100 to 150 mm, compacting each one. Stone tipped from a lorry and raked flat is not a foundation.
The pad should run 300 to 500 mm past the container footprint on every side, and something firm must sit under each corner casting. Heavy paving slabs or small concrete pads bedded into the stone spread that point load. In the gravel pad vs concrete slab comparison, this is where gravel earns its place. Our site preparation guide covers the access side.
- Suits: farms, yards, industrial land, soft ground that can drain.
- Fails on: peat, made ground, clay hollows with no outfall, unrestrained slopes.
- Lifespan and reversibility: decades with a top up every few years, and fully reversible.
- Cost: typically 400 to 1,200 euros, varying with ground conditions, access and contractor.
When are concrete piers or pads the better option?
Concrete pads under the four corner castings suit firm or sloping ground, cost less than a slab and can be set out and poured in a day.
The standard detail is a pad around 400 by 400 mm and 150 to 200 mm thick, cast on undisturbed ground rather than backfill, and taken below the local frost line. Frost depths and permit rules differ by country and municipality, so check locally. Structural design across Europe follows the Eurocodes.
Four pads carry a 20ft. A 40ft is better on six, with a pair under the side rails, because a long unit flexes once loaded. On slopes you step the pier heights instead of importing tonnes of fill. The budget version is railway sleepers or heavy paving slabs on compacted stone: cheap and quick, but timber rots and slabs tilt, so check level yearly.
- Suits: slopes, firm subsoil, gardens and sites a tipper cannot reach.
- Fails on: soft or made ground, where pads settle unevenly and twist the frame.
- Lifespan and reversibility: decades in concrete, far less in timber, and easy to dig out.
- Cost: typically 300 to 900 euros, varying with ground conditions, access and contractor.
Is a full concrete slab worth the money?
A full slab of 150 to 200 mm of reinforced concrete earns its place under workshops and forklift traffic, and is overkill for plain storage.
A proper slab means a compacted sub base, a membrane, steel mesh reinforcement and concrete poured to an even thickness, then cured. It is the only option that gives a clean surface around the unit, takes wheeled plant and can be washed down. For a workshop, office or conversion, it pays for itself.
For a plain storage box the gravel pad vs concrete slab sum is easy, because the load only ever arrives at four points sized to the dimensions and ratings in ISO 668. A slab poured dead flat also holds a film of water under the container. We ask for a fall of one to two per cent, the cheapest thing you can do for the working life of the unit.
- Suits: workshops, offices, conversions, container rows, forklift or pallet truck use.
- Fails on: budgets, and any site you may want to clear. A poor sub base cracks slabs.
- Lifespan and reversibility: 50 years or more, and not realistically reversible.
- Cost: typically 1,500 to 3,500 euros for a 20ft, varying with ground, access and contractor.
Gravel pad vs concrete slab or piers: how do they compare?
Gravel wins on cost and reversibility, piers win on speed and sloping ground, and a slab wins on load spread, cleanliness and permanence.
| Factor | Gravel pad | Concrete piers | Full slab |
|---|---|---|---|
| Build time | 1 to 2 days | 1 day plus curing | 2 to 4 days plus cure |
| Relative cost | Medium | Lowest | Highest, 3 to 4 times piers |
| Best ground | Soft, free draining subsoil | Firm subsoil, slopes | Stable ground, good sub base |
| Permanence | Semi permanent | Semi permanent | Permanent |
| Drainage | Best, water passes through | Good, ground open between pads | Worst if flat, fine with a fall |
| Reversibility | Full | Good | Poor |
The choice is really about what happens to the site later, because under a sealed steel box the performance gap between the three is small.
Which foundation do we recommend for your situation?
We recommend gravel for farms and yards, concrete pads for domestic gardens, and gravel again for a container that will be moved on soon.
A farm or yard
Build a gravel pad. The ground is usually compacted already, access suits a tipper, and the pad doubles as hardstanding for vehicles. Slabs under the corners, fall to a ditch.
A domestic garden
Use concrete pads. Gardens rarely have access for lorry loads of stone, the result is tidier and you keep the lawn. Six pads for a 40ft, four for a 20ft. Ask your municipality what applies first.
A container moving again within a few years
Gravel, without hesitation. It can be re graded when the unit leaves and nothing has to be broken out. We also plan delivery and collection around a stone pad more easily than around finished concrete.
What else do people ask about container foundations?
These are the questions we field every week, on levelling, frost heave and whether a container really needs a foundation at all.
Can a container sit straight on the ground?
It can, and we deliver onto compacted hardstanding regularly. The risk is that a soft spot lets a corner drop, the frame twists and the doors bind. On grass, expect movement in the first winter.
How level does the foundation have to be?
Aim for within 10 mm across the unit. Doors start to bind at roughly 10 to 25 mm out of level, and a door that is hard to close means the frame is already twisted.
Do I need to go below the frost line?
For concrete pads, yes, or frost heave lifts corners unevenly. Frost depths and permit rules differ by country and municipality, so check locally rather than copying a figure from elsewhere.
Last updated: September 2026
Not sure which of the three fits your plot? Tell us the site and the ground, and we will advise on the foundation and quote the unit to go on it. See our containers here.
