Whether you are living in a cold climate, hot climate, or somewhere in between, you will want to know these insulation tips to control how much heat is allowed to travel into and out of your shipping container house. Some insulation will soak up moisture while others will prevent it from passing through.
The best insulation for a shipping container is closed cell spray foam. Although it is the most expensive type of insulation available and requires a professional to install it, closed cell spray foam has the highest R-value per inch, will fill irregular voids, and can help keep the home water tight.
In order to better understand the value of closed cell spray foam, let’s look at the basic fundamentals of why insulation is necessary, how insulation is measured and how closed cell spray foam compares with other types of insulation.
Why is Insulation Necessary?
According to energy.gov, insulation provides resistance to heat flow. As a result, it lowers your heating and cooling costs while improving comfort.
Know Where You Want to Keep the Heat
Heat always travels towards cooler areas. If you live in a cold climate, you will want to keep the heat inside your home.
If you live in a warmer climate, you will want to keep the heat from coming into your home. If you live in a moderate climate region, you will want to be able to allow the heat to travel one way on cooler days and the other way during warmer times.
Three Ways that Heat Travels
Heat travels either by conduction, convection, or radiation.
If a pan is placed over a flame, the pan heats up. Conduction is when the heat travels up from the hot pan through the metal handle.
Convection is when the heat is traveling through liquids and gases. This is why heat rises above denser, cooler air.
Radiant heat travels in a straight line and will heat up anything in its path.
How Insulation Works
Insulation works by reducing the amount of heat that travels through a construction assembly (such as walls, ceilings, roofing, or floors) via conduction.
In a lesser degree, insulation also reduces the amount of convective heat flow.
Radiant heat is controlled by using radiant heat barriers like reflective insulation systems, such as foil or a lighter color paint.
What R-Values Mean
R-value is how much an insulation material is resistant to conductive heat flow. The higher the R-value, the more resistant to how much heat will be allowed to conduct through a construction assembly.
Some factors that affect the amount of R-value an insulation system provides are the types used, thickness, density, temperature, age of the insulation material, and how much moisture has accumulated within it.
On a side note, when measuring the resistance of heat flow through glass, R-Value is not a typical unit of measurement. For glass, the U-Value is used. U-Value is simply the inverse of the R-Value (1/R-value).
How Much R-Value Do You Need?
R-value is how much an insulation material is resistant to conductive heat flow. The higher the R-value, the more resistant to how much heat will be allowed to conduct through a construction assembly.
Some factors that affect the amount of R-value an insulation system provides are the types used, thickness, density, temperature, age of the insulation material, and how much moisture has accumulated within it.
On a side note, when measuring the resistance of heat flow through glass, R-Value is not a typical unit of measurement. For glass, the U-Value is used. U-Value is simply the inverse of the R-Value (1/R-value).
How Much R-Value Do You Need?
The amount of R-value you will need to have in your insulation at the attics, walls, floors, and crawl spaces is determined by which climate zone your shipping container is built.
Check if your country has a map that shows different climate zones. In the United State of America, the Department of Energy (at energy.gov) has a helpful map that can be used as a guide.
If you are building in South Africa, go to this website link for a South Africa Climate Zone Map.
If you are building in Australia, go to this website link for a Australia Climate Zone Map.
All of Alaska is in Zone 7 except for the following Boroughs in Zone 8:
Bethel, Dellingham, Fairbanks N. Star, Nome, North Slope, Northwest Arctic, Southeast Fairbanks, Wade Hampton, Yukon-Koyukuk
Zone 1 includes Hawaii, Guam, Puerto Rico, and the Virgin Islands.
A national hardware and construction retail store, Home Depot, has posted a great table to follow that shows how much R-Value you will need for the various climate Zones (at https://www.homedepot.com/c/ab/insulation-r-value-chart/9ba683603be9fa5395fab9091a9131f ).
This table is indicating what the R-value would be in walls built with metal or wood studs (2×4 and 2×6). We can still use these values to insulate the existing metal corrugated walls of shipping containers.
Closed Cell Spray Foam Insulation Compared to Other Insulation Types
| Insulation Types | R-Value per inch | Cost Comparison |
| Insulated Panels | 8.0 | $$$$ |
| Closed Cell Spray Foam Insulation | 6.6 | $$$$$ |
| Rigid Foam Board | 4.5 | $$$ |
| Kraft Covered Batt | 4.3 | $$ |
| Blown in blanket system (BIB) | 4.3 | $$ |
| Open Cell Spray foam | 3.8 | $$$$ |
| Damp Spray Cellulose | 3.8 | $$$$ |
| Cotton (Repurposed blue jeans) | 3.5 | $ |
| Blankets: Batt and Roll Insulation | 2.5 | $ |
Insulated Panels Are Not a Good Solution
Insulated panels comprises of a rigid foam sandwiched between a metal or manufactured wooden faces. They are great for the construction of metal buildings. But, except for Reefers, the metal walls of shipping containers are not made with insulated panels. Refer to my article about what Reefers are at https://liveinacontainer.com/what-types-of-shipping-containers-are-best-for-homes/
Disadvantages of using Insulated panels includes the need to have exact cuts so air and water gaps are not present. They have to be tight fitted. The R-value often decreases over time as the insulation begins to deteriorate. And some insulated panels are not safe in a fire because they can be flammable and toxic.
At first glance, it appears that insulated panels would be the best choice for our shipping container’s insulation system. But, for the purposes of adding an insulation system to a shipping container home, we will not be considering the use of insulated panels.
Here’s Why Closed Cell Spray Foam Insulation is the Best Choice
Closed Cell Spray Foam is medium density and is semi-rigid. This adds to the structural strength of the surface it is applied upon.
When applied as a full coverage, it will provide a very good air seal. Especially because it will easily fill irregular voids.
Also when applied directly to the interior surfaces, it will provide an excellent vapor retarder. But, be careful not to trap any air between the insulation and the metal surfaces of the shipping container because condensation could form and cause rusting.
Because it is not permeable, closed cell spray foam is a good choice for flood-prone areas and insulation under a raised floor. It is recognized as a flood resistant material by FEMA (https://www.fema.gov/media-library-data/20130726-1502-20490-4764/fema_tb_2_rev1.pdf )
Take a look at the charts and tables above. You will see that you can obtain an R-21 value in walls using a little more than 3 inches of closed cell spray foam. It would require almost 8 – 1/ 2 inches of batt insulation to accomplish the same amount of insulation R-value.
Space is precious in shipping containers. So, reducing the wall to wall dimension by 6” instead of 17 inches is a significant advantage.
There are one-ply applications available in spray cans. These can be used to cover a limited amount of surface area.
Two-part closed cell spray foam has a lower vapor permeance and can be applied in colder temperatures than open cell spray foam insulation
This type of insulation is applied by combining two parts to the nozzle of the sprayer.
One disadvantage of using closed cell spray insulation is that it needs to be installed by a professional who is trained to use the spray gun. It is also the most expensive type of insulation.
Another disadvantage is that everyone needs to stay out of the area where the spray on foam is being applied. It is very smelly while being sprayed on surfaces and requires the right gear for those who work with it.
Other construction work will need to be scheduled around the spraying of insulation period.
Rigid Foam Board as an Insulation
Styrofoam is a popular type of rigid foam board used for insulation. It is brittle and will need to be covered with 1/ 2 inch gypsum board or other building code approved material for fire safety.
If applied to the exterior side of the wall, it must be covered with weather proof facing.
Exterior finishes, like rainscreens, uses rigid foam board in its system. With insulation on the outside face of the wall, the metal walls of the shipping container remain insulated from the cold during cold days. This will help prevent condensation from forming along the inside face of the shipping container walls.
Because this system relies on other building materials to be part its overall insulation system, rigid board is not as effective as closed cell spray foam insulation that is all-in-one.
Batt Insulation and Kraft Covered Batt Insulation
For the DIY people, this may be your best choice. They are the most economical compared to the other types of insulation.
Batt insulation will require a lot more thickness to give the required insulation that you may want. So, be ready to forfeit some usable finished area inside your shipping container home.
If you use Kraft covered batt insulation, then you will get a little more R-value that plain batt insulation. And, the Kraft paper acts as a vapor retarder in the winter and is semi-permeable on the inside face during humid summers.
Be sure to staple the tabs of the Kraft covering onto the face of the studs that is exposed to the room. Too many contractors will short cut this and staple it to the sides of the studs that often will allow air to pass around the studs.
You might be surprised to find that a large percentage of the insulated qualities are loss with a little amount of gaps left between the insulation and the studs.
Both types will require you to wear protective eye and body protection.
Blown in Blanket (BIB) Insulation
Here’s another loose insulation that is blown into the wall cavity, like the name implies. A mesh is placed on the inside face of the studs before blowing in the loose insulation. Then, its fiber packs down under its own weight into a crowded density.
You will need to make sure that the shipping container is free from leaks. This insulation is water vaper permeable. The insulation allows the water vapor to migrate through the insulated area – that is a good thing. But, it’s not good that the insulation will not act as a water barrier like closed cell spray foam insulation will.
Open Cell Spray Foam
If your budget restricts you from using closed cell spray foam, then open cell spray foam may be another option.
The R-value is not as much as the other insulation types mentioned above but it does give a little bit of benefit that it will fill irregular voids like the closed cell spray on foam. This comes in handy when insulating the interior corrugated metal walls of the shipping container.
It is flexible and gives full coverage and provides a good air seal. But, it is water vapor semi-permeable. So, it will not seal the walls from water infiltration.
If you choose to use this insulation, hire a professional to do the job for you.
There are Three Types of Loose Fill Blown-in Insulation also to Consider
Three common loose fill blown-in insulation are fiberglass, cellulose, and rock wool. They all have their own pros and cons and all should be installed by a professional. Also, they would be applied to the walls after the studs and gypsum board is installed that would create the void for the insulation.
A hole would need to be cut into the gypsum board before the insulation can be blown into to the cavity of the walls. Afterwards, the holes would be patched and refinished to match the adjacent finished surfaces.
This is only good for walls that already exist without insulation. New construction should use a different type of insulation than loose fill blown-in insulation.
Whoever is around this stuff will need protective gear on.
Fiberglass is made from glass that is heated up and spun into small fibers. Its weight is said to be light as air and provides an R-value of about 2.5 per inch. It would require around 7.5 inches to get an insulating value of R-19.
Cellulose is made from finely shredded recycled cardboard or newspaper. They should be treated to resist mold and fire. Some are treated to resist insects. It is good for the eco-minded homeowners. Don’t let it get wet because it will get soggy and lose its R-value. The R-value of this fluffy insulation is around 3.7 per inch. It would require about five inches to obtain an R-19 value.
Rock Wool is also called “mineral wool.” It is made from the blast furnace slag. The slag is a byproduct of firing iron and iron ore. The slag is heated and mixed with other minerals. It looks like sheep’s wool after it is heated and spun. Its R-value is around 3.3 per inch and would require nearly 6 inches to obtain an R-19 insulation value. Rock wool is very expensive. It is used when the fire resistant characteristics are needed.
Cotton Insulation
This type of insulation is often a blue jeans color because that what the factories use to make it.
If you are wanting to be eco-friendly, then cotton insulation might be your best choice. Installing cotton insulation is safer than fiberglass because it does not have as many health hazards.
This denim insulation can help you earn LEED points if that is your goal. It also gives good insulation against sound transmission.
But, don’t use cotton insulation in wet environments.
Radiant Barriers
Related to insulation, you can also provide radiant barriers to control the direct that heat travels in or away from your shipping container home. This is by using foil faced insulation, light color roofing, low E glass in windows and doors.
The Choice is Yours
The technology of thermal and acoustical insulation has come a long way since builders first started insulating walls with saw dust, vermiculite, or hay (although there are building built with bales of hay even now).
Depending upon the type of climate your shipping container home is built, you may need to have your insulation installed outside of the shipping container walls instead of inside. Rainscreen systems have the insulation on the outside of the building walls.
This system requires the air and moisture barrier to be installed on the outside face of the corrugated wall, then the insulation (usually rigid foam) is installed over this barrier and often has a breathable moisture barrier on top of it.
A rainscreen panel system is connected to its own support system outside of the insulation panel.
Be sure to check with your local municipality for insulation requirements.
Follow all of the manufacturer’s instructions and use proper protection of you are installing insulation yourself.
But, it is recommended to hire a professional, especially with spray on insulation, who knows how to apply the insulation in the most economical, fastest, and most important, safest way possible.
