How To Insulate A Shipping Container

Conex container

How To Insulate A Shipping Container

So you have purchased a shipping container and are wondering what you need to do to make it ready for use? One of the most important renovations that you can look to do is to insulate the inside (and possibly the exterior) of the container.

In this article we will provide you with an overview of the what, why and how of insulating your cargo container according to your needs.

The two major reasons that you will want to consider insulating your empty steel container are: heat and humidity.

Insulated Conex container
Insulated Conex container

There are a number of factors to consider when deciding how to insulate your container: the size of container, what you are intending on using the container for (storage, office, cabin etc.), the climate where you live (tropical or temperate), the cost of insulating the container (what is your budget?), the quality and degree of insulation that your needs require.

In a nutshell, the basic shipping container is great at keeping outside air and moisture from getting inside. This is referred to as “wind and water tight” as the original use for the Conex box is to ship goods on long ocean voyages across the ocean in wet weather conditions. The boxes must be impenetrable to the elements.

You should begin your insulation decision based on your local climate. Simply put, the insulation protects from the outside weather and maintains the inside temperature inside your container. The more extreme variations in temperatures that you are subjected to, the more insulation your sea container will likely require. Builders know that wet and dry climates pose different problems for insulating buildings due to the effects of heat and humidity.


Do I need to Insulate my shipping container?

Insulation is important, not only for protection against extremes of high and low temperatures, but also to prevent condensation which causes corrosion and allows mold to grow.

Ask yourself the following questions:

Does your local climate have extreme temperature variations, like freezing winter temperatures or tropical heat waves? If not, your design may be ok without the need for heating or cooling power and less insulation.
Is your container is going to be located in a region where temperatures can get very hot or very cold? If it is, you’ll likely need a substantial layer of insulation. The containers are designed to protect from water entering from the outside environment. However, being constructed out of metal – which conducts heat easily – the containers are poor at preventing heat from being transferred through the container walls. This conduction of heat leads to a significant problem: moisture condensation inside the walls of your container, which can potentially damage the materials that you are storing inside.

If you are using your shipping container for storage, insulating the container is primarily done to protect your materials from condensation damage. For offices, security offices, living spaces where people will be working or spending time, insulation is an absolute must. For living and working spaces, insulation also helps reduce noise and reduces energy bills for heating and cooling the container.

What is the “doggy rule?”
You may have heard of the “doggy rule” when considering storing items in a container: if you wouldn’t feel ok putting your dog inside with food and water for any period of time, then it probably isn’t wise to store items that would adversely react to heat and humidity over time.


The problems with humidity inside the container

Why do we need to use insulation to control humidity inside a watertight container?
The short answer is moisture condensation. Even if you don’t live in an area with tropical heat, the sun beating down on the roof of your metal Conex box can cause the ceiling temperature to rise over 100 degrees.

The temperature rise in the ceiling causes the humidity in the air to begin to condense at the top of the container interior. This 6 inch area near the ceiling is referred to as the “sweat zone.” Water droplets start to collect on the ceiling and upper parts of the walls, resulting in what is called “container rain” or “container sweat.” Before long, this excess moisture can drip onto or leach into items stored inside the container. With the collection of moisture, mold can form, damaging the stored goods that you thought were safe.

Even without accumulating any condensation, high levels of humidity (humidity levels of 60 percent or greater) trapped inside the container over time can corrode or discolor metal surfaces. Water causes steel to rust, and your shipping container will begin to deteriorate. Higher levels of interior humidity (greater than 80 percent) can cause conditions ideal for molds to propagate, labels lose their adhesive properties and peel, and cause cardboard storage boxes to soften and begin to decay.

What temperature should you maintain in the container?
A good guideline to storing items is that the interior container temperature should be maintained at less than 80 degrees Fahrenheit and a relative humidity of between 50 to 60 percent.


What is the basic process for insulating a shipping container?
The basic process for lining insulating the interior of an empty shipping container is relatively straightforward.

steel shipping container

The first step is to build an internal frame (similar to a stud wall) on the walls inside the container.

wooden frame for insulation
Build a wooden frame for insulation

A false ceiling needs to be put in place to provide a space underneath the metal roof to line with insulation.

Your internal wall (drywall or ply wood for example) will be fixed onto this frame.

Drywall or playwood over the layer of insulation
Drywall or playwood over the layer of insulation

Then the insulation material fills the space between the internal wall and the metal wall of the cargo container.

Fill cavity with insulation
Insulation material fills the space between the internal wall and the metal wall

A shipping container may be insulated in a number of different ways – the most popular being some sort of insulation and ply-lining, or by applying a spray foam.

Creating a Vapor Barrier
In humid climates we know that the interior walls of a shipping container can “sweat” – water condensing on the inside surfaces can damage any interior construction materials like wood or drywall.
A vapor barrier can help reduce this problem. A vapor barrier is any material used for damp proofing. Commonly a plastic sheet, that prevents diffusion of moisture through the wall, floor, or ceiling.

How does insulation work?

Insulation is any material specifically designed to prevent heat energy from being conducted through the exterior walls (including floors and ceiling) of your Conex container.  The general principle that insulation works by is that the material traps air (or other gasses) in tiny cells or spaces. Heat energy is not conducted efficiently through this medium and therefore heat loss is significantly slowed.

What is the “R-value”?
The R-value is the building industry term for thermal resistance “per unit area.” and a measurement of how well the material prevents transmission of heat energy. For our purposes of cargo container insulation, the R-value is a measure of how well a two-dimensional barrier, (the layer of insulation) resists the conductive flow of heat.  The higher the R-value the more efficient the insulation material and the better the performance.

Insulation types for shipping containers
Insulation options for shipping containers

What are the options for insulating my shipping container?

Depending on your time, degree of experience, and budget, shipping container insulation can be a DIY (do it yourself) project, or, in the case of foam spraying, require paying for an expert service provider.

What are some factors in making your decision of what insulation method that is best?
Performance: How much insulation do you really need? Extreme temperatures combined with needing to spend hours in the container will determine your materials, entrapped gas, open vs closed cell structure and other technical factors.
R-value: How well the insulation material prevents transmission of heat energy. Do you require a high degree of heat protection due to extremes of temperature in your climate?
Vapor Permeability: How well an insulation type prevents vapor from leaking out of it and being retained.
Cost: Some insulation materials are very cheap (or can even be free if you are recycling waste materials). If you are looking at spray insulation (see later in the article) the price of the foam itself and the labor cost involved in hiring the contractor and their specialized equipment.
Expertise: If you are planning on doing it yourself, do you have the expertise and the tools? The ease of installation is worth considering.
Eco-friendliness: Some people are interested in converting shipping containers because they want to use sustainable, environmentally friendly materials.  Different insulation materials vary significantly in the ecological impacts of their manufacture and chemical makeup.

How much does it cost to insulate my shipping container?
This is not an easy, straightforward questions to answer, due to the many variables that we outlined in the previous section. For a DIY project with lumber for framing, recycled materials for insulation (see eco-friendly insulation options list), your cost might be a only few hundred dollars.

A higher end and popular choice is spray foam insulation.  A web search produced the following quotes – although your local service provider may vary.
“Shipping container insulation packages that range from $1,581.00 to $1,938.60 for standard 20-foot containers with 8-foot ceilings.
$2,897.00 to $3,556.20 for 40-foot containers with high cube 9-foot ceilings.”


What are the different types of insulation material?
Depending on what you are using your shipping container for, any material with insulating properties can be used as insulation material.
The insulation material is placed within the wooden frame, then covered with either ply or drywall or plywood sheets.

Here is a list of the most commonly used insulation materials
Rockwool – Is one of the cheapest options and performs well in temperature control. It is not suggested for a housing use however.
Kingspan – Is a popular brand that is a little more expensive. This insulation will allow for thinner wall layers, maximizing the interior space inside your container.


What are some Eco Friendly insulation options?
For those people who are looking for environmentally friendly options, there are a number of possible choices. Some people choose natural, renewable fibers – like wool, cotton, or cellulose insulation made from recycled paper or cork – for their insulation materials.
Cotton Insulation – Made from recycled, post-consumer denim and cotton sourced from used jeans and other clothing product remnants.  Cotton insulation has an R-Value of 3.5 per inch, comparable to fiberglass insulation.
Cotton denim insulation is usually treated with boric acid, which acts as a natural fire retardant.

Wool Insulation – A popular renewable and natural material is sheep wool. Wool has an R-value of 3.5 per inch, comparable to fiberglass, denim, or other natural, fibrous insulation materials. The lanolin makeup in sheep wool is a natural fire retardant. Therefore, it is unnecessary to treat the wool with additional flame retardant chemicals.

Cork Insulation – Is a renewable and biodegradable materials sourced from the bark of trees. If noise is a factor for you (like in a workshop), a cork acoustic buffer between the metal walls of the container and the interior can reduce the noise significantly.


Spray Foam
Spray Foam might be the most popular form of insulation for insulating a steel Conex container. Spray foam is the insulation of choice when the container is used to store temperature-sensitive assets, like paper documents, certain types of electronic equipment, and computer components.

spray foam insulation
Applying the spray foam insulation

Spray foam provides a seamless vapor barrier, has a high R-value and is quicker to apply than other forms of insulation.

The spray foam method is costlier than conventional insulation due to both materials, specialty equipment required for installation and the professional labor for application that may be required.
The upside is that it’s quicker to apply because spraying may not require any extra building, such as false ceilings or wooden framing.

Spray foam insulation
Spray foam insulation application

The layer of foam insulation will also serve to lock in any toxins in the paint (VOCs that could off-gas) that coats the inside of metal walls, sealing them so they are harmless.

What are the other benefits of this option ?
Foam provides a sound barrier, it won’t settle and clump over time the way some natural fibers do, foam is highly mold, fungus and bacteria resistant.

Foam insulation for shipping containers
Foam insulation for shipping containers

Icynene® is the industry leading spray foam insulation for protecting against condensation and insulation issues inside cargo containers.


General tips on insulating your shipping container to reduce the effects of temperature and humidity

Position your shipping container in a shaded area
Install a roof over the container to reflect the sun light. Painting the exterior of your container white reduces the temperature within the container by reflecting the sun’s rays.
Install extractor fans and or air vents to control the air flow. The main considerations in condensation control are proper ventilation and dehumidification
If climate control is of critical importance, consider installing an air conditioner or dehumidifier
Mount a container on a foundation for elevation that allows air flow under the floor and affords easier moving
Interior air flow inside can discourage mold, so arrange susceptible items with space between them
There are commercial desiccants – chemical products like Container Dri or DampRid. Placed inside the container they will collect moisture from the humid air.
An inexpensive, dessicant is kitty litter. A few open bags placed inside the container will absorb moisture from the atmosphere.
Periodically monitor humidity with a moisture meter to detect excess moisture build up
Clear the roof of leaves and moss as they may trap moisture
Be cautious about storing any materials with a high moisture content