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Shipping containers were designed to move freight across oceans. Not to be lived in. Not to be offices. Not to sit in 40°C Australian sun.
Yet we keep converting them into site sheds, homes, pop-ups and plant rooms. Then we wonder why they overheat.
Here’s what’s actually happening.
A standard container is made from corrugated corten steel. Steel has high thermal conductivity. That means it absorbs heat quickly and transfers it straight through.
Under direct sun, a dark steel surface can exceed 60–70°C. The interior surface follows. Air inside heats rapidly because there is almost no resistance between outside and inside.
Steel does not slow heat down. It accelerates it.
Reference on steel thermal conductivity:
https://www.engineeringtoolbox.com/thermal-conductivity-metals-d_858.html
Most people think “air temperature” is the problem. It isn’t.
Solar radiation is.
Roughly 53% of solar energy is near-infrared, 44% visible light, and only 3% UV. The near-infrared is what carries the heat load. When that radiation hits the steel roof and walls, it is absorbed and converted into thermal energy.
The container does not just get warm. It gets loaded with radiant energy.
NASA solar spectrum reference:
https://science.nasa.gov/ems/09_visiblelight/
Brick and concrete have mass. Timber walls have cavities. Insulated roofs have layers.
A container wall is a thin steel sheet.
That means:
In summer, it spikes fast. In winter, it drops fast. There is no moderation.
Research on lightweight building overheating risk:
https://www.sciencedirect.com/science/article/pii/S0378778812001513
Here is where most conversions go wrong.
They insulate internally.
That slows conductive heat transfer into the room. But it does nothing to stop the steel skin from reaching extreme temperatures.
So what happens?
You are managing the symptom, not the cause.
The cause is external radiant load.
If the external surface hits 70°C, the internal environment is fighting a losing battle from the start.
Lower the surface temperature and everything changes:
The envelope controls the outcome.
This is well recognised in cool roof research where high solar reflectance reduces roof surface temperatures dramatically compared to dark materials.
US Department of Energy Cool Roof overview:
https://www.energy.gov/energysaver/cool-roofs
If containers overheat because they absorb radiation, then the solution is obvious.
Stop the absorption.
Surface thermal science matters more than bulk insulation in thin steel structures.
A high performance ceramic coating applied externally can:
Because containers have no depth, managing the skin is everything.
When you reduce the surface heat load, you stabilise the structure.
Shipping containers become ovens because:
You cannot fix a radiation problem with internal R-value alone.
Control the surface. Control the heat.
That is where real performance begins.
If you want, I can now turn this into a LinkedIn version with stronger hooks and a graphic focused on reflectance and surface temperature reduction.
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