Shipping Container Insulation — The Regis School, Bognor Regis
From failing roof to finished system
The Challenge
A steel shipping container is a sealed box with no thermal break anywhere in its shell. Overnight the steel drops below the dew point of the air trapped inside. Moisture condenses on the underside of the roof and runs down the walls — and in the morning it drips back onto whatever is stored below.
The trade name for it is container rain, and it does two kinds of damage. It corrodes the container from the inside, working outwards from every rib and fixing line. And it ruins what is being stored: sports kit, equipment, paper records, anything that does not appreciate being rained on indoors.
At the Arena Sports Centre the ceiling told the whole story — rust blooming along the ribs, corrosion streaking down the panels, and condensation droplets still sitting on the paint when the photographs were taken. The school had been living with it for years.
Project file
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The Solution — step by step
Why not a dehumidifier, or board insulation?
There are three usual answers to a damp container, and two of them keep costing money. A dehumidifier or desiccant removes moisture from the air after it has entered, and needs power, maintenance and replacement indefinitely. Ventilation exchanges inside air for outside air, which does not help when the outside air is also damp — and it compromises security.
Board or batt insulation is the one that looks right and is not. It adds thermal resistance in front of the steel but leaves an air gap behind it, so moist air still travels through to the cold steel and condenses there, out of sight. That is worse than no insulation at all, because the corrosion continues where nobody can see it.
Spray-applied closed-cell foam has no gap to travel through. It hits the steel in liquid form, expands, and cures to the exact profile of the corrugation — bonded across its whole area, with no cavity behind it. There is no longer a cold surface for moisture to condense on, which is why it solves the problem rather than managing it.
The system
Duratite specified 25 mm of closed-cell spray foam applied to walls, ends and ceiling — a full internal encapsulation rather than a ceiling-only treatment.
Ceiling-only is offered and is cheaper, but it leaves the walls as an untreated cold surface and the condensation simply relocates. The school opted for the full encapsulation so the container would be dealt with once rather than revisited. A 40-foot container presents approximately 115 m² of internal surface once the corrugation profile is accounted for.
In a closed-cell foam each cell is sealed from its neighbours, so the cured layer is a vapour-resistant, self-supporting insulant rather than a sponge. That is what allows it to sit permanently against a steel shell in a damp environment.
The container we refused to insulate
Two 40-foot containers were booked, deposits paid, and the team travelled to Bognor Regis on 11 June 2026 to treat both.
When the school emptied the first container ahead of the works, it started to leak — it had not been leaking when the job was booked. On opening it up that morning, our installers advised against insulating it.
The reasoning is simple. Closed-cell foam bonds to the substrate and seals it. Spray it over a container that is taking water in through the shell and you have not solved anything: you have concealed an active leak behind a permanent lining, where it will keep corroding the steel out of sight and the foam will be blamed for it later.
The school agreed on the spot. One container was treated that day, the second was left alone, and the invoice was amended down to reflect the single container rather than the two that had been booked. The leaking container can be insulated once its shell is repaired.
The Outcome
Approximately 115 m² of internal surface — walls, ends, ceiling and door leaves — now sits under 25 mm of bonded closed-cell foam. The steel is no longer a condensing surface, so the container has stopped raining on its own contents and the corrosion that was spreading from the ribs is arrested.
It took one visit, on an operating school site, with no power supply to install, nothing to service and nothing to replace. Internal corrosion is what takes a storage container out of service, so removing the condensation extends the useful life of an asset the school already owns — and the thermal benefit comes with it.
Duratite Building Products issued the 25-year material warranty and Duratite Projects the 10-year workmanship warranty on 18 June 2026, a week after the install.
On the roof — the full picture
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