2 Definitions of Condensation:

1. Atmospheric moisture that has condensed because of cold
2. The process of changing from a gas to a liquid or solid state.

Condensation in Shipping Containers

Condensation can occur within 8ft, 10ft, 20ft and 40ft shipping containers, but it occurs mainly on the roof interior and top 6 inches of the interior side-walls. The moisture can generally be from storing damp or wet goods inside the container along with high and low temperatures outside the shipping container.

In order to correct this, the shipping container needs good ventilation and be dehumidified.

We have many solutions to this problem.

1. Vents

Container vents are 10 holes punched into the steel wall with an external bracket over the top to enable good airflow, but still keeping the container watertight.

Shipping container vents

When you see a typical shipping container fitted with vents you will usually notice the vents are located on each side of the unit, just below the top rail. With a second hand unit, they generally have 2 or 4 vents. With a new build shipping container, they can either have 4, 8 or 10 vents. Some of the new containers come with vents on the side only or on the doors and the opposite wall. The vents are positioned approx.. 6 inches below the top rail of the shipping container.

As long as the container is filled with bone dry goods/equipment then the storage container should be fine closed up for at least 2 years, if not longer.

If you need to access your storage container, as many of you do, then this is when condensation can occur. If the weather is particularly cold and misty when you open the unit and then you close the doors, the weather can bring on condensation.

We recommend you ensure that your goods are not stacked up against the walls or the ceilings, to ensure air flow.

If you think the container has insufficient vents, then we can fit more for an extra cost.

In our experience the small ventilation points at the end or the side of the shipping container often prove to be adequate, but would container vents alone be good enough for you?

Here are few other ideas that might better suit your requirements.

2. De-humidifiers

De-humidifiers are readily available in many outlets. We recommend a company called: Wilms UK Ltd. Here is their website for more information about the type of equipment they offer.

The de-humidifier collects moisture from the closed container and fills a bucket with purified water. This bucket would need to be emptied on a regular basis to avoid re-circulation of the moisture. The amount of moisture accumulated is dependent on how many times the doors are opened and what the weather is doing.

This type of equipment requires external electrical supply. A hole may need to be drilled through the side walls to place a cable, in order to get access to the electrical supply.

3. Absorpoles

When you buy a new suit, you will often find a little pack of calcium chloride (also known as desiccant) crystals in the pocket. Well this is what an absorb pole is made from.

The Absorpoles can be hung from the lashing rings inside the shipping container; they usually sit inside the corrugation on the interior side walls.

Click the button below to purchase absorpoles – WE ONLY deliver to a UK address

See our Instruction sheet

This method is effective, you will need approx.. 4 for a 20ft storage container and up to 6 in a 40ft storage container. These will need to be replaced periodically. Expiration varies depending on the type and condition of the goods/equipment you are storing, the weather conditions and the number of times you will open and shut the doors.

4. Grafo-therm Paint

Grafo-Therm paint is a coating sprayed onto various surfaces, in this case corrugated steel surfaces, which can insulate the storage container and retains some moisture. This is a long term solution, proving it to be inexpensive compared to some of the other solutions.

For more information, please click on logo below:

This anti-condensation coating is typically applied to the container roof interior and the top 6 inches of the interior side-walls using spray applicators. This only works as long as the doors are opened on a regular basis, so the moisture can be expelled from the shipping container.

Interior roof of a shipping container coated with Grafotherm

5. Container lining

There is another solution, that is by lining the interior of a shipping container with 50mm of polystyrene and finish it with melamine. We do not offer this, as it is often cheaper for the customer to do it themselves.

Shipping container with lining, this was subsequently made into a site office

This can be a good way of reducing condensation but please do consider that lining will not remove the risk completely as condensation is airborne. Absorpoles, Dehumidifiers and/or heaters might still be required in order to balance the temperature in the storage container.

Conclusion

We have offered you many solutions to the problems of condensation in a steel storage container, however, only one of the these solutions will completely expel condensation in shipping containers and that’s the Absorpoles.

There are many factors that need to be taken into account, such as;

1. The type of goods/equipment you are going to store inside
2. How you store the goods
3. The location of the container
4. The weather
5. How often you will open and shut the doors.

Please note that many of our customers have used shipping containers with just vents for static storage purposes for a long time and they have not experienced excessive problems with condensation in shipping containers. We are, however, aware that there may be an exception to the rule. Absorpoles will absorb any excess moisture, but they do need replacing periodically.

If you have any questions about any of these solutions, then please call me on 0800 121 7388

About Jane Billing
Jane Billing has over 30 years in shipping container supply. During that time Jane has earned a very broad knowledge of the whole shipping container industry. From construction, to shipping, to adaption and conversions, if you have a question about any aspect of the shipping container industry Jane will likely have the answer for you. After many years working for some of the biggest names in the shipping container industry Jane set up her own company, Billie Box Ltd in 2012. Since launching in 2012 Billie Box Ltd has sold well over 1500 new and used containers.
Jane Billing