5 Methods to Insulate Your Shipping Container Home

Design & Build

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Insulation is the material that separates you and your comfortable room of conditioned air from the extreme temperatures outdoors.  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 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.  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.

Why would a container home need insulation?

Just like all enclosed structures with climate control, a container home has to separate the conditioned airspace from the outdoors.  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 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 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 for your container.  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’.

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.

Factors to consider when choosing shipping container insulation

Deciding on the ‘best’ insulation 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:

  • 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
  • Net Interior Space – Directly correlated with R-value, how much space is left-over in the interior of your container after accounting for necessary insulation and interior wall surfaces
  • Air Leakage – How well the insulation prevents air from flowing through it and around its edges
  • 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 is worth considering.
  • Eco-friendliness – As we discussed in Why Do People Live In Shipping Container Homes, 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 from 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 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!

Non-traditional Insulation

This category of insulation is made up of materials that somewhat unconventional, and often have a green factor in their selection.  Their performance makes them less suitable for most owners unless the eco-friendliness is your highest consideration.

  • 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.

Blanket Insulation

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:

  • Fiberglass – Made from superheated sand or recycled glass that is spun into thin fibers
  • Rock/Mineral/Slag Wool – Similar to fiberglass, but made from minerals/ceramics, or from ‘slag’, a byproduct of metal production
  • Sheep’s Wool – Just like it sounds, insulation made from the sheared wool of sheep
  • Cotton – 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 prevention 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.

Loose Fill Insulation

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.

  • Cellulose – Made from recycled paper products that are shredded, then blown in by machine
  • Loose Fill Fiberglass – Similar to fiberglass batts, but less dense and not tightly bound so that it can be blown in by machine
  • Vermiculite/Perlite – 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 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.  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.

  • Polyurethane foam (PU)
    • Open Cell Variety – 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 – 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
  • Polystyrene foam
    • Extruded (EPS) – Composed of small plastic beads that are fused together
    • Expanded (XPS) – Begins as a molten material that is pressed out of a form into sheets
  • Polyisocyanurate (Polyiso) – Similar to polyurethane, but with more rigidity

Spray Foam Insulation

Spray foam can be made out of several materials that are all applied by spraying out a mixture that expands into a solid.  Due to its application, spray foam creates a monolithic, continuous piece of foam that expanded in nooks, crannies, and cracks.  However, it does require trimming as the expansion will push the foam past the face of your studs.  closed cell variants can see the gases leave the cells and cause a reduced R-value over time.  air tightness.  adhesion.

  • Polyurethane Spray Foam (PSF)
    • Open Celled – The less desirable type of polyurethane spray foam, as it has a lower R-value per inch
    • Closed Celled – The classic shipping container insulation, and what we recommend for the vast majority of owners.  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.
  • Cementitious foam – An extremely light mixture that resembled concrete when cured, but shaving cream when first applied.  It is similar in R-value to PSF, but can be a bit crumbly after curing if you aren’t careful with it.
  • Cellulose – 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 at the point of application (called damp-spraying), which binds the cellulose together and enables it to be applield to open-sided wall cavities.

Other Thermal Energy Control Ideas That Aren’t Really “Insulation”

Green Roof

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.

Reflective/Radiant Barriers

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.  They often contain microscopic particles that cause substantial performance differences compared to pain despite similar appearances.

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 this technique varies dramatically based on your location’s 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.

Summary

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 on the underneath of 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.

For more related information, check out our articles on how to keep your container cool and how to keep your container warm.

Let us know below what you think of the various insulation options available to shipping container home builders.

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