Shipping containers provide secure storage for tools, stock, furniture, machinery and equipment, but condensation can become a problem if moisture inside the container is not managed.
Shipping container condensation usually occurs when warm, moisture-containing air comes into contact with a colder metal surface. Water can then form on the inside of the roof and walls.
If condensation becomes severe, stored items may become damp. Over time, this can affect cardboard packaging, furniture, fabrics, documents, tools and some electrical equipment.
The good news is that there are several ways to reduce the risk.
Why Does Condensation Form Inside Shipping Containers?
Air contains water vapour. When warm, humid air meets the cold steel walls or roof of a container, the air can cool below its dew point and water droplets can form.
This is similar to the condensation you might see on a cold window.
Temperature changes between day and night can increase the risk, particularly when moisture is already present inside the container.
Common sources include:
- Damp goods
- Wet tools and machinery
- Timber containing moisture
- Wet clothing or fabrics
- Moisture rising from the ground
- Humid outside air
- Poor airflow
Controlling moisture and temperature changes can help with keeping container contents dry.
Start with a Wind and Watertight Container
Before thinking about condensation control, make sure rainwater cannot enter the container.
Check the roof, walls and doors for damage. Door seals should be in good condition, and the container should close correctly.
Unit Group’s standard shipping containers for hire include wind and watertight options suitable for a wide range of storage requirements.
Remember that a watertight container can still develop internal condensation. Preventing rain from entering and controlling moisture already inside are two different issues.
Make Sure the Container Is Properly Ventilated
Ventilation can help moist air escape and allow fresh air to circulate.
Standard shipping containers normally have vents, so avoid blocking them with boxes, shelving or stored equipment.
For storage uses that create higher humidity, additional ventilation may be worth considering.
The right approach depends on what is being stored, the location of the container and how frequently it is accessed.
Never Store Wet Items
One of the simplest ways to reduce shipping container condensation is to avoid introducing unnecessary moisture.
Allow wet tools, machinery and equipment to dry before putting them into storage.
Be particularly careful with timber, fabrics, furniture and other materials that can retain moisture.
A container packed with damp goods may have a much greater condensation problem than one loaded with dry contents.
Leave Space for Air to Circulate
Avoid packing stock tightly against the steel walls and roof.
Leaving a small gap allows air to move around stored goods and reduces direct contact with cold metal surfaces.
Where practical, use shelving or racking to keep smaller items organised and off the floor.
This also makes it easier to inspect the container and spot signs of moisture before stored items are affected.
Consider Moisture Absorbers
Desiccants and container moisture absorbers can help remove water vapour from the air.
These can be useful where the contents are particularly sensitive to damp or where the container will remain closed for extended periods.
The quantity and type required will depend on the container size, climate, contents and expected storage period.
Moisture absorbers should be checked and replaced according to their manufacturer’s instructions rather than fitted and forgotten.
Would Insulation Help?
Insulation can reduce the temperature difference between the internal air and steel surfaces.
This may be useful for containers used for longer-term storage or when the contents are particularly sensitive to changes in temperature and humidity.
Several approaches are available, including insulated linings and specialist container modifications.
If you expect to use the unit for a long period, discuss the intended contents with Unit Group before deciding whether a standard container or specialist option is more appropriate.
Unit Group also supplies specialist containers for requirements where a standard storage unit may not be suitable.
Choose the Container Location Carefully
Where you position the container can affect conditions inside it.
The ground should be firm, reasonably level and well drained. Standing water around the container can increase moisture around the storage area.
Our guide to shipping container foundations explains the differences between concrete, tarmac and compacted gravel bases.
Good drainage also helps keep the surrounding area accessible during wet weather.
Protect Moisture-Sensitive Items
Some stored goods need additional protection even when the container itself is dry.
Cardboard boxes can absorb moisture, so plastic storage boxes may be more suitable for sensitive items.
Furniture can be covered with breathable protective materials. Metal tools and machinery may also require appropriate corrosion protection when being stored for long periods.
Avoid wrapping damp items tightly in plastic because this can trap existing moisture.
Inspect the Container Regularly
Do not assume everything is fine simply because the doors have remained closed.
Regular checks allow you to identify condensation before it causes damage.
Look for:
- Water droplets on the roof
- Damp walls
- Wet packaging
- Musty smells
- Mould
- Rust on tools or equipment
- Damp patches on the floor
If condensation appears, identify the source of moisture and review the ventilation, contents and storage arrangement.
What Should You Store in a Standard Container?
Standard containers can be suitable for many everyday storage requirements, including tools, equipment, building materials, furniture and packaged stock.
However, goods requiring tightly controlled temperatures or humidity may need specialist storage.
If you are unsure, explain exactly what you intend to store when requesting a container quote.
Our recent guide on converting a shipping container into secure storage also covers ventilation, insulation and other storage improvements.
Frequently Asked Questions
Is condensation normal in shipping containers?
Will ventilation stop container condensation?
Can I store furniture in a shipping container?
Can condensation damage tools?
Keep Your Shipping Container Contents Dry
Preventing condensation starts with keeping unnecessary moisture out.
Choose a wind and watertight container, store dry items, maintain ventilation and leave space for air circulation. For longer-term or sensitive storage, consider moisture absorbers, insulation or a specialist container.
Unit Group can help you choose a suitable container based on what you plan to store and how long you need the additional space.