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Inside the treated storage container at The Regis School: walls, ceiling and end in a continuous cream closed-cell layer, the corrugations still legible beneath it.
Project recordEncapsulated inside

Project record · Shipping containers · School

The Regis School, Bognor Regis: a container that stopped raining inside, and one we refused to spray.

Two steel storage containers at a secondary school, rusting from the inside as condensation formed on the cold steel and dripped onto the equipment stored beneath it. On 11 June 2026 one was emptied, sheeted and fully encapsulated inside at 25 mm, walls, ends, ceiling and door leaves, in a single day. The second had an active leak, so we left it alone and reduced the invoice.

≈115m²
Internal surface encapsulated
25mm
Closed-cell, every internal face
1 day
On site, 11 June 2026
1 of 2
Containers treated; one refused

01The building

A steel box that rained on what it was meant to protect.

A shipping container is a thin steel shell with nothing between its inside and the weather. Schools use them for storage because they are cheap and secure. What they are not is dry: the steel runs cold, the air inside carries moisture, and the result is what people call container rain.

Container rain. Overnight the steel cools below the dew point of the air inside. Water forms on the ceiling and the upper walls, gathers along the corrugations and drips. The contents get wet and the steel rusts from the inside, which is what the school was finding.

Why it is a condensation job. There is no leak to fix, in a sound container. The fix is to make the inside face of the steel a warm surface, so the air inside never meets a cold one. That means a bonded insulating layer on every internal face, doors included.

Two containers booked. Both were to be treated on the same day. One was. The other, on inspection, had an active leak through the shell, and spraying over a leak is something we do not do. More on that below.

Buildings
Steel storage containers, school site
Client
The Regis School
Location
Bognor Regis, West Sussex
Treated
One container: walls, ends, ceiling and door leaves, inside
Area
About 115 m² of internal surface
Application
25 mm closed-cell, full internal encapsulation
Date
11 June 2026, one day
Not treated
Second container, active leak; invoice reduced

02What we specified, and why

25 mm of closed-cell on every internal face, door leaves included.

Condensation control is a 25 mm job: enough to keep the inside face of the steel above the dew point of the air in the box. The point is coverage, not depth. A single bare corner is a single place for water to form.

  • The system: closed-cell, at 25 mm, inside. Sprayed to the corrugated walls, both ends, the ceiling and the inside of the door leaves, following every corrugation and closing at the floor line. How thickness follows the objective.
  • Why closed-cell on steel. It bonds to the metal and sets rigid, so the inside face of the shell becomes the foam, not the steel. The water vapour resistance factor (μ) of 62 that NexSeal LE declares to BS EN 12086 is the figure the condensation-risk analysis uses for a box like this.
  • Why the doors too. Door leaves are the largest cold surface a container has after the roof, and they are the one people forget. Leaving them bare moves the condensation; it does not stop it.
  • What 25 mm does not do. It controls condensation. It is not a thermal upgrade that makes a container warm to work in, and we do not describe it as one. Shipping containers, the building type.
Product
Closed-cell spray foam
Depth
25 mm
Faces
Walls, ends, ceiling, door leaves, inside
Objective
Condensation control
The inside of a container door leaf after the work: the corrugated steel of the door in a continuous cream closed-cell layer, the locking bars left clear.

The door leaves. The faces most people leave bare, encapsulated with the rest, the locking gear kept clear. Project record.

Photographs · Project record

Rust, sheeting, foam, finished. One day.

The corrosion the school was living with, the container emptied and sheeted, the layer going onto the corrugations, and the finished interior.

Before: rust streaks on the corrugated steel ribs inside the container where condensation had been running.
Project recordBefore: rust on the ribs
Before: corrosion across the container ceiling from condensation forming on the cold steel.
Project recordBefore: the ceiling
Preparation: the container emptied and sheeted, the floor protected before spraying.
Project recordPrep: emptied and sheeted
During: closed-cell foam on the corrugated wall, following each rib of the steel.
Project recordDuring: on the corrugations
After: the inside of a door leaf fully encapsulated in closed-cell foam.
Project recordAfter: door leaf
After: the full-length interior of the container, walls, ceiling and end in one continuous cream layer.
Project recordAfter: full length

Photographs from the job, as it ran. Labelled Project record because they are.All project records

03How the work ran

Empty, inspect, sheet, spray, hand back. And one refusal.

A single day on a school site. The container was emptied and inspected, sheeted, sprayed on every internal face and handed back. The second container was inspected and declined.

  1. Empty and inspect

    Both containers opened and looked at.

    Contents out, the shells inspected for condition. The first was sound and wet from condensation. The second had an active leak through the shell.

  2. Sheet

    Floor and fittings protected.

    The first container's floor sheeted, the door gear and any fixings masked, containment set so nothing left the box.

  3. Spray

    Every internal face, 25 mm.

    Closed-cell applied to the walls, both ends, the ceiling and the inside of the door leaves, following the corrugations, in a single visit.

  4. Hand back

    One container, one invoice line.

    The treated container handed back the same day. The second left as found, and the invoice amended to a single container.

04The outcome

Condensation stopped at the source, and a straight answer on the second box.

Reported by the school and recorded by us. The warranty position is stated as it stands.

Container rain

Stoppedat the source

The inside face of the steel is now the foam; the air in the box no longer meets a cold surface.

Internal surface

≈115m²at 25 mm

Walls, ends, ceiling and door leaves, one continuous layer.

Time on site

1 day11 June 2026

Emptied, sheeted, sprayed and handed back in a single visit.

The second container

Declinedactive leak

Left as found and taken off the invoice. The leak comes first.

Where this record comes from

Warranty. HOLVEM’s 25-year workmanship warranty, plus the manufacturer’s 25-year product warranty, issued directly by the manufacturer.

Yours will differ. A container used as a workspace is a different objective from one used for storage. Shipping containers.

05Where this record leads

If this looks like your containers.

The building type, the school context, and the corrosion problem this record started from.

Your next step

Your building.
Your brief.
A specialist.

If you already know the U-value or thickness you need, tell us and we price to it. If you do not, tell us what you know about the building and the problem, and we work it out with you. Someone who does this every day reads it and comes back to you.

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Or pick up the phone

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