You likely need insulation for your shipping container home, but what kind of insulation is best?
In this Article
This article will answer all your questions about shipping container insulation. Storage container homes are popular these days, but you need to know what it takes to truly turn them into a living space.
We will first examine the most relevant considerations in choosing a type of insulation, then we will examine the insulation types you can choose from, and we will conclude with some insulation alternatives.
You may have heard that polyurethane spray foam insulation is the only variety worth considering for shipping containers. As you’ll find out below, that’s not always the case.
Our goal with this article is to give you a comprehensive guide to not only understanding insulation generally but also how to choose the type of insulation that is most relevant to your needs. This can include factors such as the size of the container, geography and climate, as well as insulation-specific attributes like price, quality, and more.
With that said, let’s start with a discussion of controlling factors and the various types of home insulation.
What is 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. Otherwise, you’re air conditioning the neighborhood (something you may have heard from your parents when you left the front door open!)
If you built the walls around your porch out of newspaper or plastic food wrap, they wouldn’t be very effective at regulating the temperate (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. So even though the air is seperated, your energy efficiency would be quite low.
Therefore, insulation is a material specifically designed to prevent heat energy from moving through the walls (and ceiling, and floor) of your shipping container 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.
Why do you need container home insulation?
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, insulating material helps keep the heat from the warmer side from moving to the cooler side. This increases the energy efficiency of your container home by lowering the amount of energy needed to regulate the internal temperature.
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 steel is at conducting thermal energy, it is especially ineffective at keeping your airspace at a different temperature than the air outside. Therefore, insulation is often needed more for shipping container homes than for other construction types.
And let’s not forget that the steel of a container home can absorb a tremendous amount of radiant energy from the summer sun, actually getting hotter than the ambient air. Simply stated, unmodified shipping containers are great at keeping outside air from getting inside. However, they perform poorly at keeping heat from moving through their walls.
Nevertheless, 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.
How climate affects your insulation decision
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 insulation material for your shipping container. Areas like southern California and parts of the Mediterranean feature what many consider to be an ideal climate.
With that said, 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 storage containers, but you don’t HAVE to. You’d need to weigh the costs of insulating (a one-time cost) versus the ongoing heating and cooling costs to run your air conditioner and/or heater.
You might also need a larger air conditioner or heater than you otherwise would if you had insulated your container. Over time, any money saved from not insulating quickly disappears as you pay more and more for energy to keep the climate in your shipping container tolerable.
To summarize, unless you live in the best possible climate, you are likely going to need to insulate your cargo container. And if you choose to forgo insulation, there’s a real chance you will regret it due to all the extra money you will need to be spending on heating and cooling. You will definitely appreciate the benefits of an insulated shipping container far more often than not.
One note of caution: If you don’t insulate your container, not only will your home be harder to heat and cool, it may also be susceptible to water condensation, which can lead to an assortment of problems like corrosion and mold.
Where to place your container insulation
Most building types have multiple layers of materials in their walls. The surface you see inside is not the same material as what’s outside. In between are several layers of materials that provide structure, fire resistance, weatherproofing, thermal insulation, vapor barrier, etc.
With shipping container homes, the container itself is one such layer. And you have to make a decision on where the container skin will be located in the overall wall system.
The most conventional answer is to place insulation within the interior walls, inside the shipping container. These stud walls are added to most designs anyway as a place to run plumbing and electrical service, as well as an attachment point for drywall or other interior surfaces. It only makes sense to add insulation in the cavities between the studs. Then you can more or less leave the outside of the container as-is if you want.
However, for some people, exterior insulation is a better fit. In this case, you place insulation outside of the container and then cover that insulation with some type of weather-resistant sheathing. This provides the benefit of increased interior space and a more controlled exterior appearance for those who want to shield or hide the shipping containers themselves.
Factors to consider when choosing insulation
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 the specific conditions of your shipping containers.
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:
- Overall Performance: Performance characteristics are affected by things like material, entrapped gas, open vs closed cell structure, etc.
- R-value: How well the material prevents transmission of heat energy for a given thickness
- Air Leakage: How well the insulation prevents air from flowing through it (which as already discussed, is a separate but related issue from blocking heat transfer)
- Vapor Permeability: How well the insulation prevents vapor from migrating through it and staying in it
- Cost: Factor in both material costs and labor/equipment costs depending on if you’re doing it yourself or hiring a contractor. Remember if you’re doing it yourself, ease of installation and required tools are worth considering.
- Eco-friendliness: Many people are attracted to shipping container homes because they want to build and live in a sustainable, environmentally friendly manner. These materials vary quite a bit in the ecological impacts of their manufacture and installation.
Types of Shipping Container Insulation
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 one category below if it can be purchased and applied in different ways (we’re looking at you, polyurethane foam and cellulose).
The most important part of recognizing the differences between materials and determining how they affect your personal circumstances so you can choose the best type of insulation for your situation. 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 considered ‘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.
While these are certainly economical forms of insulation, their practicality is not generally very high. They might be suitable for more moderate climates, where the temperature fluctuations aren’t as extreme.
- Straw Bale: Much like the straw bale you might use to feed a horse, but instead stacked like blocks. Due to the size of straw bales, this would only work for insulation on the exterior of the container
- Hempcrete: A material similar to concrete but with less strength, and made out of hemp.
Coming in the form of insulation 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:
- Fiberglass Insulation: Made from superheated sand or recycled glass that is spun into thin fibers. In western countries, this is the most common type of cheap wall insulation.
- Slag Wool, Mineral Wool, and Rock Wool Insulation: Similar to fiberglass, but made from minerals/ceramics, or from ‘slag’, a byproduct of metal production
- Sheep Wool Insulation: Just like it sounds, insulation made from the sheared wool of sheep
- Cotton or Denim Insulation: Made from cotton, often with a blue-ish color as much of it is sourced from recycled denim or blue jeans. Pricier, but with a very high percentage of recycled contents
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 by adding a second barrier, you can end up trapping water vapor in the 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 on your floor.
- Cellulose Insulation: Made from recycled paper products that are shredded, then blown in by machine
- Loose-Fill Fiberglass Insulation: Similar to fiberglass batts, but less dense and not tightly bound so that it can be blown in by machine
- Vermiculite Insulation and Perlite Insulation: Minerals that have been heated and expanded like popcorn, making a sort of natural foam pellet that can be added to wall cavities
Given their vapor permeability, loose-fill insulation materials aren’t really recommended for containers.
Expanded Foam Insulation
Expanded foam is manufactured offsite into large boards and insulation panels that are pre-sized for typical wall heights. Unlike blanket insulation, these insulation panels are self-supporting. Holes for things like doors and windows are made on-site by cutting. Just like with spray foam insulation, the gas in closed cell expanded foam variants can sometimes escape the cells and cause a reduced R-value over time.
Expanded foam 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.
- Open Cell Polyurethane Foam Insulation (oc PU Foam): Open-cell foam cells are not as dense and are filled with air, which gives the insulation a spongy texture and a lower R-value.
- Closed Cell Polyurethane Foam Insulation (cc PU Foam): The ‘blowing agent’ fills the tiny microscopic cells with a gas other than air that has better heat conduction properties, increasing the R-value of the foam
- Extruded Polystyrene Foam Insulation (EPS): Composed of small plastic beads that are fused together into a closed cell foam. It’s the white foam you’re familiar seeing in the form of things like coffee cups, and it’s what the shipping container insulation kits from companies like InSoFast are made of.
- Expanded Polystyrene Foam Insulation (XPS): Begins as a molten material that is pressed out of a form into closed cell foam sheets. While the name is similar to EPS, it’s quite a bit different.
- Polyisocyanurate (Polyiso): Similar to polyurethane, but with more rigidity
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.
Spray foam 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.
- Open-Cell Spray Polyurethane Foam (ocSPF): The less desirable type of polyurethane spray foam insulation, as it has a lower R-value per inch due to the allowance of air movement between cells.
- Closed-Cell Spray Polyurethane Foam (ccSPF): The most common shipping container insulation, and what we recommend for the majority of owners. This type of spray foam insulation provides one of the highest R-values per inch and forms a nice vapor retarder. There is some concern with off-gassing after spray application, so be sure to check with your manufacturer about cure times and how long to wait before occupancy. The gas in these closed-cell variants can sometimes escape the cells and cause a reduced R-value over several years.
A separate but related option is non-expanding sprayed-in insulation. Unlike the spray foam insulation types above, it doesn’t chemically expand upon application, but it does move around to fill up the cavity completely.
- Damp-Spray Cellulose Insulation: Made from recycled paper products that are shredded. As opposed to the normal blown-in application, a special rig can be used that adds water or adhesives at the point of application (called damp-spraying), which binds the cellulose together and enables it to be applied to open-sided wall cavities.
- Cementitious Foam Insulation: An extremely light mixture of water, air, and natural minerals that resembles concrete when cured, but shaving cream when first applied, and can be a bit crumbly after curing if you aren’t careful with it. However, thanks to its ingredients, cementitious foam is eco-friendly, non-toxic, and non-flammable despite lagging behind spray foam insulation in R-value.
As you can see, the options available are quite extensive. Choosing the best insulation for you really requires a proper understanding of your own decision making factors, like budget, climate, design, and personal tolerance to hot and cold.
If you are in doubt, take a look at what people in your geographic area are already doing. It’s often easier and cheaper to use materials that are already common for your region. A conversation with a local construction contractor to get site-specific recommendations and advice may also be useful.
Refrigerated Shipping Containers
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 was used to carry cold products like flowers and produce. There are a lot of pros and cons to this option, but it can be a good choice if you can find these containers at a reasonable price.
Other Thermal Energy Control Ideas That Aren’t Really “Insulation”
A green or living roof is a rooftop garden of sorts made 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 more traditional forms of insulation, but a supplement to it.
An additional benefit of green roofs is that they look cool! From the sky, your container home will look like just another patch of ground. And while it’s not a great option for insulation it’s still an environmentally conscious choice and does add an element of protection.
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.
Unless you’re open to draping your container with a mylar space blanket like 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 specially formulated to reflect the invisible infrared light of thermal energy, and though they may look similar to paint, they work much differently.
Passive Heating and Cooling Design
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 varies 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.
Making a Decision
As you might have gathered, a common theme running throughout this article is the vast number of options available when it comes to shipping container home insulation. But always remember that insulation is just one part of a broader plan and building design.
You need to consider container home insulation in the context of your overall needs and architectural ideas. It has to be a consideration from day one, as it affects almost every later decision. It also needs to fit into your overall budget and account for factors such as climate, ease or difficulty of installation, size of the build, personal preference, and more.
We want to make sure you are satisfied with your shipping container home. As they say, happiness is reality minus your expectations.
By understanding the realities of financial resources and physics, plus managing your expectations surrounding things like interior comfort, you’ll end up with a project you love! So start early and develop a clear vision for your shipping container construction dream.
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.