Are Shipping Containers Waterproof and Airtight?

Shipping containers have long been known for their strength and durability when travelling overseas. However, with many different uses available for them today, it’s important to understand how waterproof and airtight they are before you get started on a project. 

Whether you’re using a container for storage, conversion, or transportation, ensuring your unit is waterproof and airtight is essential for protecting your goods and ensuring durability and longevity. 

What makes a shipping container waterproof?

Since shipping containers were originally designed and used to transport goods in rough seas and harsh weather conditions, they have certain waterproof features. However, the level of waterproofness of a shipping container depends on a number of factors, including its design, condition, and how well it is maintained – or has been maintained if you’re purchasing a used container.

By regularly inspecting your container, carrying out proactive maintenance, and installing thoughtful modifications, you can ensure your shipping container remains watertight for longer, no matter what you decide to use it for.

Design

For the most part, shipping containers are all designed in the same way, using corrugated steel to create a robust structure. This steel offers durability and resistance to water ingress, but over time, it can become weakened, which is why regular maintenance is so important. 

Shipping containers are also often designed with rubber seals around the doors which are intended to keep water from entering. Ensuring these seals remain intact and in good condition is essential for keeping your container waterproof. Finally, the welding on corners and seams of your shipping container can influence how well the waterproofing of your container is – another key area to inspect during regular maintenance checks.

Age and condition

If you’ve opted to buy a used shipping container, its age and condition will be particularly important when establishing its level of waterproofing. Long-term exposure to moisture or dampness can lead to rust, especially on the roof and corners, which can create weak points for water to seep through. Dents, scratches, and damage during transportation can also impact the unit’s waterproof nature, particularly if there is damage to the roof or near seams where it is easier for water to enter. 

Additionally, over time, the rubber gaskets around your shipping container doors can degrade, leading to easy entry for water. Checking for these issues before you buy your container is essential, as is consistently inspecting and maintaining the unit once it has been installed on your site to ensure any issues are rectified early.

Environmental exposure

The environment your container is placed in will also have an impact on its waterproofness. Shipping containers in humid or coastal areas are more likely to succumb to rust or corrosion because they are constantly exposed to moisture and salty air. Likewise, heavy rain or snow can take its toll on the waterproofing of a container. 

With most shipping containers having a flat roof, water pooling can also be a cause for concern. When this happens, there is an increased risk of leaks, particularly if the container already has some cracks or rust. Modifying your container to suit the environmental conditions is key to ensuring its waterproofness for longer.

Maintenance and repairs

Once your shipping container has been installed, carrying out regular maintenance and repairs is essential for ensuring it stays as waterproof as possible. Using protective coatings, such as marine-grade paint, can decrease the chance of rust forming and seal small imperfections. Without carrying out regular maintenance and protective measures, your container will be at greater risk of water damage, potentially leading to exterior rust and condensation which can impact the interior. 

As part of these checks, you should look for rust, leaks, and any damage that could lead to a bigger problem or water ingress. Even minor issues should be rectified as these can quickly lead to bigger problems without you even noticing. It’s also essential to ensure your repair works are carried out to a high standard, as poorly executed repairs can create new weak points and lead to further damage.

Modifications

While a major benefit of shipping containers is their adaptability and ability to modify them extensively, this can also be problematic if waterproofing measures are not taken seriously. When you add windows, doors, or vents to a shipping container, you could compromise the waterproof nature if you do not ensure they are sealed properly with weatherproof materials. We always advise speaking with a professional for these types of works to make sure they are carried out to a high standard. 

If you’re planning to combine multiple containers to create a larger structure, you will need to ensure the joints and seams have been thoroughly sealed to prevent water infiltration. Professional welders will be able to help you with this, ensuring your structure can stand the test of time and battle the elements.

Type and history of the container

No matter what you’re using a shipping container for, you’ll need to decide whether to buy a new or used unit. On one hand, new containers are often in pristine condition and offer a higher level of waterproofing than used containers which could have been exposed to many years of wear and tear. However, they are typically more expensive, so it could be worth considering a used option and repairing it to ensure it is waterproof.

In addition to the condition of the container, size and type also make a difference. High-cube containers have more internal volume due to their increased height, which means they may be more likely to experience roof sagging or water pooling if they are not reinforced correctly. 

It’s also a good idea to do some research to find out what your container was used for in a previous life. This can help you establish how long it might last and how much work you need to complete to ensure its waterproofness. For example, containers used to transport corrosive or hazardous materials may have interior damage that could compromise the waterproofing.

Waterproof vs watertight 

While the terms “waterproof” and “watertight” both seem to mean the same thing, they’re actually quite different. The main difference between them is that “waterproof” materials are completely impermeable to water, while “watertight” materials prevent water from entering under specific conditions.

In terms of shipping containers, a waterproof container is built to withstand extreme wet weather conditions and even water submersion. They offer a superior level of waterproofing. Watertight shipping containers, on the other hand, are designed to stop water from entering the unit in normal conditions, like rain or splashing waves at sea.

Are shipping containers airtight?

Shipping containers are not completely airtight, but they are still designed to offer security and weather resistance. It’s important that shipping containers are not completely airtight so that air can move through the unit. Most standard shipping containers have small vents along the top rail that allow air to circulate, preventing condensation in the container and other moisture problems. 

As shipping containers can be customised to create many different usable spaces, such as living quarters, workshops, or storage units, you can improve air circulation by installing ventilation systems that help manage the airflow while controlling air exchange between the inside and outside. 

The level of airtightness in a shipping container is not standardised and should be adjusted depending on the use of the unit. For example, you may need a specific level of airtightness to protect sensitive goods or store chemicals.

Factors that influence how airtight a container is

There are a number of factors that influence how airtight a shipping container is, such as the doors, vents, and unit condition. Before you start modifying or using your container, you should assess each of the factors to establish your unit’s level of airtightness.

• Condition: Used containers may be less airtight than new units, especially if rust, dents, and other everyday use have compromised the shipping container’s ability to seal air.
• Doors: Shipping container doors are heavy-duty, with rubber gaskets creating a tight seal that keeps moisture, wind, and pests out. However, these seals are not designed to make the container completely airtight, and over time, they can degrade and allow more air to enter.
• Construction: With corrugated steel walls, roofs, and floors, shipping containers have a solid construction, making them highly durable. They are designed to keep cargo secure while minimising air exchange, but over time, the construction of a container can become less robust due to wear and tear.
• Ventilation: Without modification, most shipping containers have small vents that prevent the buildup of condensation during transit. They allow a limited amount of airflow into the container, ensuring it is not fully airtight with plenty of ventilation. If you’re planning to buy a used shipping container, it’s important to check these vents to ensure they still work effectively. 
• Welding: Shipping containers are welded together at the seams and joints which support the airtightness of the unit. However, over time, these welded seams and joints could develop imperfections that reduce their effectiveness, particularly if they have been damaged or used heavily.
• Modifications: If you’ve customised or are planning to customise your container, it’s essential that you understand the implications this can lead to. Windows, doors, and other openings can reduce the airtightness of the container if they are not properly sealed with airtight materials. 

Ways to make a shipping container waterproof and airtight

Depending on the condition of your shipping container and its intended use, you may need to make it more waterproof or airtight. There are several ways to do this.

Inspect the container

The first step in ensuring waterproofing and airtightness of your shipping container is to thoroughly inspect it. This includes both inside and outside. On the exterior of your container, you should look for rust, dents, cracks, and any damage to the walls, roofs, and corners, as this can impact how effectively the unit performs.

You should check the rubber gaskets around the doors for any gaps or wear, while also ensuring all seams and joints are robust without any signs of weakness or openings. Finally, inspect your vents to find out whether they are allowing air or water ingress. 

Repair structural issues

Once you’ve identified any weaknesses or structural issues with your container, it’s time to repair them. This should be done as part of your regular shipping container maintenance and repairs, not just once you receive your unit. 

If you’ve found holes or cracks in the walls, seams, or roof, you can use metal patches or welding to seal them. Be sure to consult a professional when it comes to welding. If your container has rust issues, you can sandblast the surface rust away before applying a rust inhibitor to prevent any further corrosion.

Seal the doors

Shipping container doors are often a common place for waterproofing and airtightness to fail. It’s therefore essential to replace any damaged gaskets with new, high-quality gaskets that ensure a tight seal. Once this has been done, test your work by closing the doors tightly to check for any gaps. You should adjust the hinges and latches if gaps are still occurring. As a final step you can apply a waterproof sealant to the door edges for additional protection.

Waterproof the exterior

To further improve waterproofing, you should apply protective coatings on the walls, roof, and welded seams. Marine-grade or industrial paint designed to resist water and UV damage should be used for this. Alternatively, adding certain types of cladding to your container can help to ensure your container is more waterproof. 

On the roof of your unit, a rubberised membrane can prevent pooling or leaks, while gutters or sloped roofs can also help to redirect water away from the standard flat container roof.

Make the container airtight

Next, you should improve the airtightness of the shipping container by checking and modifying the vents. You can seal existing vents by welding the ventilation ports shut or replacing them with adjustable, airtight vents, depending on how airtight you need the unit to be. 

To enhance airtightness, you should apply industrial sealant to the seams, joints, and around the window and door frames. For this, you can use high-quality silicone or polyurethane sealant. To check the effectiveness of your work, use smoke or a pressure test to identify and seal any remaining leaks. 

Address modifications

For containers that have been modified, such as with the addition of windows or doors, it’s vital you check they are properly installed with weatherproof and airtight seals. If you’re not sure, it’s best to consult a professional. Openings for utility connections should also be sealed with expanding foam or rubber gaskets to prevent water and air from entering the shipping container.

The bottom line

Ensuring your shipping container is waterproof and airtight is vital, whether you’re using it as a living space, office, storage, or for transporting goods. Following our top tips for waterproofing and airtightness can help you prolong the life of your shipping container and ensure its contents are always protected from the elements.

FAQs

Can a shipping container withstand a flood?

The strong construction of shipping containers ensures they can withstand harsh environmental conditions, including floods. The steel exterior of a shipping container is designed to protect the contents inside from high water levels. In addition, shipping containers can be elevated or anchored to prevent them from being swept away by floodwater. However, it’s important that shipping containers are properly maintained to ensure their construction is durable enough to withstand a flood.

Can water get into shipping containers?

Unfortunately, it is possible for water to get into a shipping container. This happens for a range of reasons, from poor sealing, damage, or extreme weather conditions. Shipping containers should be properly sealed and inspected before loading for transportation or modified as living space. If you’re storing or transporting, you should also ensure waterproof packaging is used as an extra layer of protection.