How to insulate a container from heat and cold is what I want to show you today. Insulation is the material that keeps you and your living space comfortably separated from extreme temperatures outside.
You likely need insulation for your container home, but what type of insulation is best? The answer can vary depending on your situation and goals, so let’s discuss the control factors and different types of insulation.
What does insulating a container from heat and cold mean?
If you had an outdoor porch or patio that gets hot in the summer, would you air-condition it? No, not without enclosing it by building walls first, of course!
You want to keep the conditioned air separate from the outside air, whether it’s cooled or intentionally heated depending on the season. But if you built the walls around your porch using newspaper or plastic, they wouldn’t be very effective, although they would keep the air separated.
Why not? A thin wall cannot effectively prevent heat transfer from the hot side to the cold side. While actual air cannot move through the wall, the heat contained in the air CAN move through the wall material.
We recommend checking out our article on heat transfer in container homes! Therefore, insulation exists as a material specifically designed to prevent thermal energy from moving through the walls, roof, and floor of your home.
It typically works by trapping air or other gases in a complex matrix of tiny cells or passages. Compared to solids and liquids, gases conduct thermal energy poorly, making them excellent insulators.
By confining the gases to millions of tiny cells, it limits the role of convection within the gas, further enhancing the insulation properties of the material.
In most cases, when we talk about thermal insulation, we’re specifically referring to conductive heat flow and, to a lesser extent, convection.
The resistance to this heat flow is measured using an “R-value,” which coincidentally is the insulation rating—the higher, the better. Heat flow through radiation comes into play, as explained below.
Why does a container home need insulation?
Like all enclosed structures with temperature control, a container home needs to separate the conditioned airspace from the exterior.
As explained earlier, insulation helps prevent heat from the hotter side moving to the colder side.
Unlike some more traditional types of residential construction, container homes have the additional problem of an all-steel exterior.
Given how conductive steel is, it becomes especially ineffective at maintaining your airspace at a different temperature from the outside air. Therefore, insulation is more necessary for container homes than for other types of construction.
However, just because container homes are poor at preventing heat transfer doesn’t automatically mean you need insulation. The other factor to consider is the climate.
How to insulate a container from heat and cold?
If you’re fortunate to live in a place with a climate suitable for living without additional cooling or heating, you may not need insulation for your container.
Areas like Southern California and parts of the Mediterranean enjoy what many consider an ideal climate. However, some people still require heating and air conditioning in these climates and should therefore consider insulation.
Whether or not you need climate control for your container home largely depends on your personal preferences for what is “comfortable” to you. If you don’t live in such a place, I highly recommend insulating your container.
You’ll need to consider the insulation costs, which are a one-time expense, versus the ongoing cost of additional electricity to run your air conditioning and the gas or fuel to power your heater.
You may choose not to insulate your container, in which case, you’ll also need a larger air conditioner or heater than you would if you insulated your container home. Over time, the money saved by not insulating disappears quickly as you pay more and more to keep the climate in your home tolerable.
However, a word of caution: If you don’t insulate your container home, not only will it be harder to heat and cool your home, but it can also be susceptible to condensation, which can lead to a variety of problems like corrosion and mold.
Our two-part series on condensation delves into this in-depth and is a must-read for all prospective container home owners.
Factors to consider when choosing container insulation
Deciding on the best insulation is less straightforward than you might think. Each type of insulation has advantages and disadvantages that may or may not be particularly relevant to your specific situation and project.
I’ll do my best to provide a high-level discussion of some of these criteria as we talk about each type of insulation. However, please note that there may be some variability depending on the region and manufacturer, so always do your own research.
The key factors to consider when evaluating your insulation options include:
- Performance: Performance characteristics are influenced by elements such as the material, trapped gas, open or closed-cell structure, etc.
- R-value: How well does the material prevent the transmission of thermal energy?
- Net interior space: It is directly related to the R-value, how much space is left inside your container after accounting for the necessary insulation and interior surfaces of the walls?
- Air leakage: How well does the insulation prevent air from flowing through it and around its edges?
- Vapor permeability: How well does the insulation prevent vapor from migrating through it and staying within it?
- Cost: Consider both material costs and labor costs, depending on whether you do it yourself or hire professionals. If you do it yourself, it’s worth considering the ease of installation.
- Environmental friendliness: As explained in “Why do people live in container homes,” many people are attracted to container homes because they want to build and live in a sustainable, environmentally-friendly manner. These materials vary widely in their ecological impacts of manufacturing and installation.
Types of insulation for containers
There are five broad categories of insulation we’ll discuss here, grouped by the physical form they take, which is closely related to how they are applied. Different types of insulation can fit into different categories, and some insulating materials may fit into more than one category.
They can be purchased and applied in different ways, such as polyurethane foam and cellulose. That being said, let’s jump into the different options!
This category of insulation consists of unconventional materials that often have a green factor in their selection. Their performance makes them less suitable for most homeowners unless ecological consideration is your primary concern.
- Straw Bale: Similar to the straw bales you might use to feed a horse but stacked like blocks. Due to the size of straw bales, this would only work for exterior insulation of the container.
- Hempcrete: A material similar to concrete but with less strength and made from hemp. Hempcrete or Hemplime is a biocomposite material, a mixture of hemp shives and lime used as a construction and insulation material. It is marketed under names like Hempcrete, Canobiote, Canosmose, and Isochanvre.
In the form of batts (pre-cut lengths to fit typical wall heights) and rolls (long rolled pieces that need to be cut to length during installation), blanket insulation is somewhat “fluffy,” compressible, and non-self-supporting.
It’s very similar to the blanket you might use to keep warm in your home on a winter night, except it’s thicker and made of different materials. In almost all cases, blanket insulation makes use of long fibers crushed into a small space, effectively creating open cells.
Blanket insulation is designed to be fitted into cavities between studs and uses them for structural rigidity, as it would simply fall onto a pile without support. It is one of the cheapest options and is very easy to install as it usually only requires a staple gun to fasten the studs.
Varieties of blanket insulation include:
- Fiberglass: Made from overheated sand or recycled glass that is turned into thin fibers.
- Rock/Mineral/Slag Wool: Similar to fiberglass but made from minerals/ceramics or “slag,” a byproduct of metal production.
- Sheep’s Wool: Just as it sounds, insulation made from sheared sheep’s wool.
- Cotton: Made from cotton often with a bluish color, as much of it comes from recycled denim pants. It is more expensive but has a high percentage of recycled content.
Blanket insulation is fairly vapor-permeable, which in traditional construction can be mitigated with a vapor retarder.
However, as mentioned in our condensation prevention article, vapor retarders are generally not a good option for container homes because the external metal cover is already a vapor barrier in itself and can end up trapping water vapor in the wall cavities.
Some of the fibers used to make blanket insulation, especially fiberglass, can irritate the eyes, skin, and respiratory systems.
Proper personal protective equipment (PPE), such as a dust mask, gloves, and safety glasses, is necessary before handling these materials.
Refer to the Material Safety Data Sheet (MSDS) or other instructions on the product packaging for proper handling procedures.
Loose Fill Insulation:
This type of insulation relies on the application of small macroscopic pieces (easily visible to the naked eye) of insulating media into a wall cavity.
These insulators typically require complete containment of the wall cavity before application, otherwise, you’ll just have a pile on your floor.
- Cellulose: Made from recycled paper products that are shredded and then blown in with a machine.
- Loose-fill Fiberglass: Similar to fiberglass batts but less dense and not tightly bound so they can be blown in with a machine.
- Vermiculite/Perlite: Minerals that have been heated and expanded like popcorn, producing a kind of natural foam pellet that can be added to wall cavities.
The term “pellet” (also pelet) is a generic designation used to refer to small portions of agglomerated or compressed material made from different materials.
Due to their vapor permeability, loose-fill insulation materials are not recommended for containers.
Expanded Foam Insulation:
Expanded foam is manufactured off-site in large boards and panels that are pre-sized for typical ceiling heights. Unlike blanket insulation, it is self-supporting. Holes for things like doors and windows are made on-site by cutting.
Gas in closed-cell variants can sometimes escape from the cells and cause reduced R-value over time. It is DIY-friendly and can be attached to studs or even glued directly to the container. It can be quite quick to install unless you have to make many cuts.
Some varieties are molded to match the corrugations of a container wall. If not, you’ll have large air gaps in these corrugated areas.
Expanded foam insulation, in most cases, has the highest R-value per inch of all the insulation materials described in this article.
- Polyurethane Foam (PU):
- Open-cell: Open-cell foam cells are not as dense and filled with air, giving the insulation a spongy texture and a lower R-value.
- Closed-cell: The “blowing agent” fills the tiny microscopic cells with a gas other than air that has better heat-conducting properties, increasing the R-value of the foam.
- Polystyrene Foam:
- Extruded (EPS): Made up of small plastic beads that are fused together.
- Expanded (XPS): Starts as a melted material that is pulled from a form to form sheets.
- Polyisocyanurate (Polyiso): Similar to polyurethane but with more rigidity.
Spray Foam Insulation:
Spray foam can be made from various materials, which are applied by spraying a mixture that expands into a solid. Due to its application, spray foam creates a monolithic and continuous piece of foam that expands into corners and cracks.
However, it requires trimming as the expansion will push the foam beyond the surface of the studs. Closed-cell variants may see gases escaping from the cells and cause reduced R-value over time: air sealing and adhesion.
- Spray Polyurethane Foam (SPF):
- Open-cell: The least desirable type of spray polyurethane foam as it has a lower R-value per inch.
- Closed-cell: The classic container insulation and what we recommend for the vast majority of homeowners. It provides one of the highest R-values per inch and forms a good vapor retarder. There is some concern with off-gassing after the spray application, so be sure to consult with your manufacturer about curing times and how long to wait before occupancy.
- Cementitious Foam: An extremely lightweight mix that looks like concrete when cured but resembles shaving cream when first applied. It is similar in R-value to SPF but can be a bit crumbly after curing if not handled carefully.
- Cellulose: Made from shredded recycled paper products. Unlike normal blown-in application, a special platform can be used that adds water at the point of application (called wet spray), which bonds the cellulose and allows it to be applied to open-sided wall cavities.
Other ideas for insulating a container from heat and cold
Thermal Energy Control:
These other ideas I’m giving you are not really “insulation,” but I want to mention them so that you are aware and this article is complete.
A green roof, also known as a living roof, is a type of garden on your roof with various herbs and other plants. The soil and plants themselves are not excellent insulators, but they can help block solar radiation if you live in a warm climate. Therefore, a green roof is not really a replacement for insulation but rather a supplement.
An additional benefit of green roofs is that they look great! From above, your container home will appear as another patch of land.
While the other types of insulation mentioned earlier work to reduce the rate of thermal energy transfer through conduction (and to a lesser extent convection), we still need to consider radiation.
As you know from our article on heat transfer in container homes, radiation is the least understood form of heat transfer but is incredibly important in container home construction.
Unless you’re open to covering your container with a mylar blanket like those used by hikers, obtaining a radiant barrier will likely involve some type of coating.
Be careful to note the difference between paint and coatings that are specifically designed to reflect and emit radiant energy.
Passive Heating and Cooling Design:
Another option is to design your home in a way that minimizes the amount of energy needed for heating and cooling.
There are various techniques that attempt to achieve this, which are beyond the scope of this article. Examples include Trombe walls, solar chimneys, and others. The effectiveness of this technique varies dramatically depending on the climate of the area where you are living.
While these passive methods can be effective in milder climates, they will not be sufficient on their own. For example, the coolest you’ll feel in a passively designed container is if you were standing outside in the shade with a breeze blowing. If even that is too hot, passive design won’t be enough.
You have plenty of options available to insulate a container, and the choices depend on factors such as your climate, design, and budget. All options have their pros and cons, but now you have a better understanding of what they are. One thing to keep in mind is that you don’t necessarily have to use a certain type of insulation exclusively.
For example, you could use closed-cell spray polyurethane foam insulation for the walls and roof of the container and then use rock wool blankets underneath the container to keep costs low. You can even combine insulation in the same area.
For instance, you could use rock wool on the bottom of the container and then spray an inch of closed-cell polyurethane foam on top of the rock wool to create an airtight seal.
Whatever you do, make sure you understand the implications of condensation if you’re in a climate where it is a concern. For related information, check out our articles on how to keep your container home cool and how to keep your container home warm during winter.
Let me know below what you think about the various insulation options available for container home construction.