Your container is poorly ventilated (even with hatches)

If you've ever opened a container after a few days of rain or a cold night in Quebec, you may have experienced the following: a blast of damp air when opening the doors, a musty smell, and sometimes even water droplets on the walls. Yet the container is equipped with ventilation hatches. So what's going on?

These little vents do have a role to play... but they're often misunderstood. When a container is used for storage, these hatches simply aren 't enough to ensure adequate ventilation. In this text, you'll learn what they're really for, why they're insufficient in static storage, and what you can do to avoid moisture problems.

What are ventilation hatches really for?

On all sea containers, you'll find between 4 and 8 ventilation hatches, generally located high up on the side walls. These openings have two main functions:

1. Balancing air pressure

The container is designed to be almost perfectly airtight. When there is a difference in pressure between the inside and the outside - which frequently happens with temperature variations or after a move - the doors can become very difficult to open or close. These hatches allow just enough air to circulate to avoid such blockages.

2. Limit condensation during transport

At sea, ambient humidity combined with temperature changes can cause condensation inside the container. These hatches help to stabilize this during the first few days of transport.

But once the container has been placed on a site in Quebec, exposed to the local climate, these hatches quickly become insufficient to manage humidity over the long term.

A typical case: a container in Laval

A construction contractor in Laval used a container to store his portable electrical equipment and bags of mortar during the autumn. After a series of cold nights followed by milder days, he noticed that condensation had formed on the ceiling and started dripping onto the tools. The result: swollen wooden handles, rust on the blades, and several cardboard boxes rendered unusable.

Yet, from the outside, everything seemed normal. The container was in good condition, and the ventilation hatches were in place. But inside, there was no way for the moisture to escape effectively.

Why these hatches aren't enough in storage

1. They create no air flow

Hatches are small, fixed and often all on the same side. There's no real circulation - just a little passive breathing. So the air inside remains stagnant, especially if the container is full.

2. They don't manage humidity

Quebec's climate is particularly variable. All it takes is a little residual humidity inside (wet objects, boots, melted snow) for the water to evaporate, condense on the ceiling, and fall back onto your belongings. The original hatches do not have the capacity to handle this humidity continuously.

3. Not designed for the long term

These hatches are designed for a few days' shipping, not several months' storage in a field in Saint-Hyacinthe or a parking lot in Trois-Rivières.

What can happen with insufficient ventilation

When air remains trapped inside a container, problems quickly appear:

• Interior condensation, especially on the ceiling, creating an indoor rain effect.

• Musty odors, even on "dry" objects.

• Mould on porous materials: wood, fabric, paper.

• Rapid corrosion of tools, equipment or metal parts.

• Degradation of your materials: hardened cement bags, warped crates, swollen furniture.

Another concrete example: a farm in the Montérégie region used a container to store seeds and harvesting equipment. When the container was reopened in the spring, several bags had become damp. Not only were the seeds unusable, but a strong odor of mold permeated the entire space.

What could be done to improve ventilation?

Fortunately, there are some simple and effective solutions.

✅ Add cross-ventilation grilles

Install:

• An air inlet at the bottom of one side of the container;

• An air outlet at the top on the other side.

This creates a natural air current that allows warm (and therefore humid) air to escape. Ideally, orient these openings according to the prevailing winds in your area.

✅ Install mechanical ventilation

For more sensitive storage or in very humid climates:

• A solar fan may suffice. It operates autonomously and forces air circulation.

• Electric ventilation with a timer or humidity sensor is also an option if you have access to electricity.

✅ Use humidity absorbers

As a complementary measure, moisture absorbers can slow the onset of condensation. They do not replace good ventilation, but offer additional protection.

In a nutshell

Ventilation hatches for shipping containers are indispensable... but only to facilitate door opening and limit air pressure during transport. In fixed storage, they are far from sufficient.

If you want to protect your equipment, materials or personal belongings from moisture and mold, you need to go further:

• Add well-placed openings;

• Promote real air circulation;

• Manage humidity, especially during cold, wet seasons.

See our article, which also explains in detail how to ensure dry storage.

A well-ventilated container is the difference between a reliable warehouse... and a box of problems.