The floor is the part of a container that does the most work and gets the least attention. It carries every load you put in, it is the first surface to suffer from damp, and it is the one component that is genuinely straightforward to repair or upgrade. Understanding what is under your feet is the difference between a deck that lasts thirty years and one that needs a panel out in three.
On this page
What the floor is actually made of
In the overwhelming majority of dry containers the floor is marine-grade plywood, usually around 28 mm thick, laid in long panels and screwed down to steel cross members that run across the width of the unit roughly a metre apart. Those cross members are welded to the bottom side rails, and it is the rails and the corner castings that carry load into the ground. The floor is a deck, not a foundation.
The plywood itself is nothing like the softwood ply you would buy for a shed. It is a dense hardwood laminate of fourteen to twenty-one plies, chosen because it flexes under a moving forklift without delaminating and because it grips a screw for decades. Newer units increasingly use bamboo composite panels, which are harder, more dimensionally stable and more sustainably sourced.
Underneath, the panels are sealed and the cross members coated. This matters more than people expect, because most floor failures start from below, where a container has sat on damp ground with no airflow beneath it. That is exactly why our foundations guide spends so long on lifting the unit clear of the ground.
Treatment, markings and what they mean
Because containers cross borders, the timber inside them has to satisfy quarantine rules in every country they enter. The plywood is therefore treated against insect and fungal attack before the container is built, and the treatment used is declared on a small plate or stencil near the door end.
Older units, particularly pre-2000, may have been treated with compounds no longer in use. Modern treatments are considerably milder, and residue in a container that has spent years in service is low. Even so, the sensible approach for anything beyond sealed pallet storage is to seal or overlay the deck. It costs very little, it makes the floor easier to sweep, and it settles the question rather than leaving you wondering.
Worth knowing: the same plate tells you the manufacturer and build year, which is genuinely useful when judging a used unit. Our terminology glossary explains each marking.
Load ratings and the point-load trap
Container floors are engineered for a loaded forklift to drive across them, which sounds reassuring until you consider how that load is distributed. A forklift spreads its weight across wide tyres and keeps moving. A jack stand, a machine leg, a narrow castor or a racking upright concentrates the same weight into a few square inches, and if that spot falls between two cross members the plywood is being asked to work as a beam.
| Load type | Behaviour | What to do |
|---|---|---|
| Palletised goods | Spread across several plies and members | Nothing. This is what the deck is designed for |
| Loaded forklift | Rolling load with a wide contact patch | Fine within the unit rating; avoid pivoting in one spot |
| Machine or plant legs | Severe point load, often between members | Bed on steel plate or hardwood bearers spanning two members |
| Pallet racking uprights | Concentrated and permanent | Bolt through to the cross members, or use spreader plates |
| Vehicle storage | Heavy but shared between four tyres | Usually fine; lay ply or steel runners if the tyres sink |
| Bulk aggregate or liquids | Very heavy and uniformly distributed | Check the unit payload first, and consider a steel or bunded floor |
The rule of thumb is simple. If the contact area of a load is smaller than your hand, spread it. A piece of steel plate under a machine leg costs almost nothing and removes the single most common cause of container floor damage.
Assessing a used floor before you buy
Floors tell you more about a used container than the paint does. A clean, dry, tight deck means the unit has been stored well and kept level. Soft patches, lifting edges and dark staining mean it has spent years somewhere damp, and that history will be present in the roof and the door seals too.
Walk the whole length
Feel for spring or give underfoot. A sound deck feels like a concrete floor, not a trampoline.
Close the doors and look up
Daylight at the roof or the door seals means water has been getting in, and the floor directly below will show it.
Check the threshold
The door threshold takes the most traffic and the most water. Lifting or splitting here is common and easy to repair.
Look for previous repairs
Mismatched panels are not a problem in themselves, but a patchwork of them suggests a hard life.
Inspect from underneath
If the unit is on blocks, look at the cross members and the underseal. Flaking coating is normal; deep pitting is not.
None of this need put you off a used unit. Our condition guide explains which grades carry a guaranteed floor standard, and every unit we sell is checked as set out in our inspection information.
Want to see the floor before you commit?
We photograph the interior of every unit we list, including the deck and the door threshold, and we will take fresh pictures of any specific container on request.
Sealing, overlaying and replacing
There are three levels of intervention, and most owners never need more than the first.
- Seal it. Sweep, wash, let it dry completely, then roll on two coats of floor sealer or epoxy floor paint. Half a day of work. It makes the deck wipeable, stops moisture wicking into the plies and seals in any historic treatment residue.
- Overlay it. Screw down exterior ply, OSB or a proprietary floor panel over the original. Adds durability, hides old damage and gives a clean substrate for vinyl or rubber. Costs a little headroom, which matters if you are lining the walls as well.
- Replace panels. Unscrew the affected bay, cut a new panel to the original thickness and screw it into the cross members. Straightforward work. Matching thickness is critical, because a step in the floor becomes both a trip hazard and a water trap.
For anything occupied — an office, a studio, a welfare unit — the floor stops being a surface and becomes part of the thermal envelope. In that case insulate above or below the deck before you finish it, as covered in our insulation guide.
Steel, mesh and composite floors
Not every container has plywood, and for some uses timber is the wrong answer entirely.
Steel and mesh floors are heavier and noisier but effectively indestructible, and a bunded tray beneath open mesh means a leaking drum stays contained rather than running out under the doors. If you are storing anything that can spill, specify this when you buy rather than trying to retrofit it later.
Flooring questions answered
Yes. Container plywood is treated against insects and fungal attack so it can cross borders without quarantine problems, and the underside is usually sealed with a bituminous coating. Modern treatments are far milder than the older compounds, and every unit carries a timber treatment marking near the door that states what was used.
For sealed, packaged goods it is not a concern. For anything in direct contact with the floor, for food preparation, or for growing, seal the floor first with a suitable coating or overlay it. It is a cheap job and it removes the question entirely.
A great deal spread out, and much less concentrated. The floor is rated for a loaded forklift traversing it, but a narrow leg or a jack stand can punch straight through the plywood between cross members. Spread point loads with steel plate or timber and you will never have a problem.
Yes, and it is the usual repair. Plywood panels are screwed to the cross members, so a damaged bay can be unscrewed and a new panel fitted without touching the rest. Matching thickness matters more than matching appearance.
For most storage use, clean it, let it dry fully and roll on two coats of a floor sealer or epoxy paint. For workshops, an epoxy or polyurethane floor coating is worth the extra. For offices and anything occupied, insulate over the plywood and finish with vinyl or laminate.
No. Steel floors, open mesh grid floors over bunded trays, and composite bamboo floors all exist. Steel and mesh suit chemical storage and wash-down environments, while bamboo is common on newer units and is harder and more stable than softwood plywood.