Insulation is the material that separates you and your comfortable room of conditioned air from the extreme temperatures outdoors. When thinking through how to insulate a shipping container, there are quite a few options with their own pros and cons. You likely need insulation for your shipping container home, but what kind of insulation is best? The answer can vary depending on your situation and goals, so let’s discuss the controlling factors and the various types of home insulation.
If you had an open-air porch or patio that is hot in the summer, would you air-condition it? Not without enclosing it by building walls first, of course! You want to keep the conditioned air (air that has been intentionally cooled or warmed, depending on the season) separate from the outside air. But if you built the walls around your porch out of newspaper or plastic food wrap, they wouldn’t be very effective (even though they would keep the air separated). Why not?
A thin wall isn’t able to prevent the transfer of heat from the warm side to the cool side very effectively. While the actual air can’t move through the wall, the heat contained in the air CAN move through the wall material. We’d recommend checking out our article on heat transfer in container homes before you go any further!
Therefore, insulation is a material specifically designed to prevent heat energy from moving through the walls (and ceiling, and floor) of your home. It generally works by trapping air or other gasses 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, you reduce the role convection plays within the gas, further increasing the material’s insulating properties.
In most cases when we talk about thermal insulation, we’re specifically talking about conductive (and to a lesser extent, convective) heat flow. The resistance to this heat flow is measured using an “R-value”, which coincidentally is how insulation is rated (higher is better). Heat flow via radiation does come into play as well as discussed below.
An important note for our readers that use the metric system (SI units): The R-values expressed in this article, elsewhere on our website, and in most American publications are based on English or inch-pound units. To convert to an SI R-value, you need to multiply by 0.1761101838. Read this Wikipedia article for more information on the unit conversion.
When insulating a shipping container, you’re separating the conditioned airspace from the outdoors. It’s the same thing you’d normally do with almost all enclosed structures that have climate control. As explained before, insulation helps keep the heat from the warmer side from moving to the cooler side.
Unlike some more traditional types of residential construction, shipping container homes have the added issue of an exterior that is completely made of steel. Given how great of a conductor steel is, it makes it especially ineffective at keeping your airspace at a different temperature than the air outside. Therefore, insulation is needed more for container homes than for other construction types.
However, just because container homes are bad at preventing heat transfer doesn’t automatically mean you need insulation. The other factor to consider is the climate.
If you are lucky enough (or easy-going enough!) to live in a location with a climate that is suitable for you to live in without additional cooling or heating, you may not need shipping container house insulation. Areas like southern California and parts of the Mediterranean feature what many consider to be an ideal climate. Nevertheless, some people still need heating and air conditioning in these climates…and thus should strongly consider insulation. Whether you will need climate control for your shipping container home or not depends on your personal preferences for what is ‘comfortable’. With additions of fans in warm climates and warm clothes in colder ones, you may be able to endure the normal temperatures without any added insulating material.
If you don’t live in such a location, then we strongly recommend you insulate your container…but you don’t HAVE to. You’d need to weigh the costs of insulating (a one-time cost) vs the ongoing cost of additional electricity to run your air conditioner and/or fuel to power your heater. You might also need a larger air conditioner or heater than you otherwise would if you insulated your container. Over time, any money saved from not insulating quickly disappears as you pay more and more to keep the climate in your home tolerable.
One note of caution though: If you don’t insulate your container, not only will your home be harder to heat and cool, it may also be susceptible to condensation, which can lead to an assortment of problems like corrosion and mold. Our article on condensation discusses this in-depth and is a must-read for all prospective container homeowners.
Deciding on the best insulation for your home is less straightforward than you think. Each type has pros and cons that may or may not be especially relevant to your particular situation and project. We’ll do our best to provide a high-level discussion of some of these criteria as we go through each type of insulation. However, know that there can be some variability depending on region and manufacturer, so always do your own research.
Main factors to consider when evaluating your insulation options include:
There are five broad categories of insulation we’re going to discuss here, grouped by the physical form they take which is closely related to how they are applied. Much like peanut butter and peanuts might fit into two different categories of food (or applesauce and apples, or… we’ll just stop there!) some insulation materials may actually fit into more than category below if it can be purchased and applied in different ways (we’re looking at you, polyurethane foam and cellulose). With that said, let’s jump into the different options!
This category of insulation is made up of materials that somewhat unconventional, often are chosen at least in part for their eco-friendliness, and are usually consider cheap insulation. Their performance makes them less suitable for most owners given their low R-value per inch unless the eco-friendliness is your highest consideration and you’re willing to sacrifice interior room for it.
Coming in the form of batts (pre-cut lengths to fit typical wall heights) and rolls (long rolled-up pieces that must be cut to length during installation), blanket insulation is somewhat “fluffy”, compressible, and not self-supporting. It’s much like the blanket you might use to keep warm in your house on a winter evening, except thicker and made of different materials. In almost all cases, blanket insulation makes use of long fibers mashed into a small space, effectively making it open-celled.
Blanket insulation is intended to be fastened in the cavities between studs and uses those studs for structural rigidity since it will just fall over into a pile without support. It is one of the cheapest options and is very easy to install, typically only requiring a stapler to fasten to studs.
Varieties of blanket insulation include:
Blanket insulation is quite permeable to water vapor, which in traditional construction can be mitigated with a vapor retarder. However, as we discussed in our condensation article, vapor retarders are usually not good choices for container homes because the outer metal skin is already a vapor barrier itself, and you can end up trapping water vapor in wall cavities.
Some of the fibers used to make blanket insulation, most noticeably fiberglass, can be irritating to eyes, skin, and respiratory systems. Proper PPE (personal protective equipment) such as a dust mask, gloves, and safety glasses is necessary before handling these materials. Consult the MSDS (Material Safety Data Sheet) or other instructions on the product packaging for proper handling procedures.
This type of insulation is based on applying small macroscopic (easily viewable with the naked eye) chunks of insulating media into a wall cavity. These insulators generally require complete wall cavity containment prior to application, otherwise, you’ll just have a pile in your floor.
Given their vapor permeability, loose-fill insulation materials aren’t really recommended for containers.
Expanded foam is manufactured offsite into large boards and panels that are pre-sized for typical wall heights. Unlike blanket insulation, it is self-supporting. Holes for things like doors and windows are made on-site by cutting. The gas in closed-cell variants can sometimes escape the cells and cause a reduced R-value over time.
It is DIY-friendly and can be attached to studs or even glued right to the container. It can be pretty quick to install unless you have a lot of cuts to make. Some varieties are molded to match the corrugations of a shipping 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 insulating materials discussed in this article.
Spray insulation can be made out of several materials that are all applied by spraying or pumping out a liquid mixture that then hardens into a solid. Due to how it is applied and adheres to itself, spray insulation is continuous and expands into nooks, crannies, and cracks. This forms a barrier that resists air movement as well as the transference of heat.
One time of spray insulation expands upon application then hardens, which helps further with sealing. However, it does require trimming as the expansion will push the foam past the face of your studs.
A separate but related option is non-expanding sprayed-in insulation. Unlike the spray foams above, it doesn’t chemically expand on application, but it does move around to fill up the cavity completely.
The majority of this article comes from the position of adding insulation to a traditional shipping container. However, there is another option: purchasing an insulated shipping container that is used to carry cold products like flowers and produce. There are a lot of pros and cons to this option, and the discussion is best addressed in our article dedicated to the subject.
A green or living roof is a garden of sorts on your roof, with various grasses and other plants. Soil and plants aren’t great insulators, but they can help to block solar radiation if you live in a warm climate. A green roof, therefore, isn’t really a replacement for insulation, but a supplement to it.
An additional benefit of green roofs is that they look cool! From the sky, your container will look like just another patch of ground.
While the other types of insulation mentioned above work to slow the transmission of heat energy via conduction (and to a lesser degree convection), we still have radiation to think about. As you know from our article on heat transfer in shipping container homes, radiation is the least understood form of heat transfer, but it’s incredibly important in shipping container construction.
Unless you’re open to draping your container with a mylar space blanket likes the ones commonly carried by hikers, getting a radiant barrier is likely going to involve a coating of some sort. Be careful to notice the difference between paint and coatings that are specifically designed to reflect and emit radiation energy. Coatings are specifically designed to reflect the invisible infrared light of thermal energy, and though they may look similar to paint, they work much differently. Our article on cool roof coatings explains this much more in-depth.
Another option is designing your home in such a way that it minimized the amount of energy needed to heat and cool it. There are a variety of 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 these techniques vary dramatically based on your climate.
While these passive methods can be effective in more temperate climates, they often won’t be enough on their own. For instance, the coolest you’ll ever feel in a passive-designed container is if you were standing outside in the shade with a breeze blowing. If even that is too hot, a passive design isn’t going to be enough.
You have quite a few insulation options at your disposal, and what you choose is driven by factors like your climate, design, and budget. All choices have their pros and cons, but now you have a better understanding of what those are.
One thing to keep in mind is that you don’t necessarily have to use a certain type of insulation exclusively. For instance, you could use closed-cell polyurethane spray foam insulation for the container walls and roof, and then use rock wool blankets underneath the container to keep the cost down. You can even combine insulation in the same area. For example, you could use rock wool underneath the container and then spray an inch of closed-cell polyurethane foam over 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.
Let us know below what you think of the various insulation options available to shipping container home builders.