What are the Best Insulation Materials?
In the majority of climate zones, all-season shipping container houses must be heated and/or cooled to create a comfortable living environment. These days, given capricious effects of global warming combined with our tightened “personal comfort zones” ability to heat or cool our houses is also expected in traditionally moderate Mediterranean of South-Californian climates.
Container-based houses in contrast to traditional ones (think – brick or stone structures) do not have any “thermal inertia” to survive even short daily periods of high temperatures. Let’s face it – exposed to sun they will become instant ovens! No wonder then, that for container houses the thermal insulation is part of the mandatory “Survival Package”.
The package that thanks to the increased energy-efficiency of our home, will also lower our costs (we are all “wallet-sensitive) and made us part of the eco-friendly movement.
In practice, our approach to this problem is determined by the class of shipping container houses:
a) Customized Container Houses (CCH) come as factory-insulated units not leaving much room for further thermal improvements;
b) Cargo Shipping Containers come as raw metal boxes and must be thermally insulated on-the-site, if intended for housing applications.
Most Important Characteristics of Insulation
Before going further (in this case selecting the insulation material) let’s shortly analyze their most important characteristics (the Table below summarizes some).
Characteristics of typical sandwich wall panels (Source: Suzhou Huahang Integrated House Co.,Ltd) hangchenghouse.com
It defines the thermal performance of the insulation material. Basically, higher R-value means better insulation barrier. In practice it means higher energy efficiency of your container house for a given thickness of the insulation or thinner insulation for a given energy efficiency.
The latter is especially important for ISO-type container-based houses because their external width is limited to 8ft (2.44m). Obviously, every extra inch of thickness of interior insulation means 2 inches narrower living space.
Rigid and spray insulation (PE, EPS, PF….) have the highest R-values.
– Vapor/moisture permeability
In contrast to traditional housing, container-based houses have built-in moisture barrier made by impermeable steel walls and roof. In cold climate zones where interior is heated, the internally generated moisture (breathing, cooking, shower…) will tend to migrate through the permeable part of the wall (sheetrock, insulation) as well as through all possible wall’s “imperfections” (fissures, electrical outlets, plumbing holes etc..) towards the cold steel wall where it will condensate.
To minimize this process as well as its effects, the insulation material should have the lowest possible moisture permeability and lowest level of water absorption. Otherwise, it’s a recipe for mold, deterioration of insulating properties (decrease of R-value) and corrosion. What makes it worse, is that until it’s too late, the effects are invisible for human eye, hidden “behind the wall”.
The closed-cell Polyurethane, Polyester and Phenolic-based insulation materials have lowest vapor permeability and water absorption (retention).
To achieve the good level of energy efficiency it is important to eliminate all possible “low heat-resistance” paths (heat bridges, air filled holes and cavities, etc..) that by the Law of Physics, heat will use to infiltrate interior or escape from it. Simply speaking – to be efficient, the insulation barrier must be continuous. The best from this point of view seem to be spray insulation as well as flexible, woolly blanket-type materials (fiberglass and mineral wool).
– Health hazards
All synthetic insulation materials (PE, EPS, PF to name few) are complex mixtures of chemical substances. These materials consist not only of high heat-transfer-resistance components but also bonding, hardening, fire and moisture retardant compounds necessary to get required properties and keep it all together. Some of them may be hazardous for health by off gassing, physical touch and inhalation.
Unfortunately, we are living in an unhealthy world so in this case it is the problem of choosing a lesser devil. T
ypically, the mineral wool and in general natural materials (cellulose, cotton, sheep wool, wood…) are quite neutral to our health. The fiberglass may cause eyes irritation and allergies when inhaled, but we live with it daily as it is the most popular insulation material used in residential construction. Mentioned synthetic insulation materials may be off gassing for long period of time (sprays quite intensively in the next few days after application). On top of that in the unfortunate case of a fire, they may release toxic gases.
Some insulation materials are inherently fire-resistant (fiberglass, Rockwool etc…). Obviously, glass and basalt can melt, but they will not sustain the fire by themselves. In contrast, most natural insulation materials (mentioned earlier wood, cellulose, wool, cotton) will burn easily and help the fire to spread.
Most synthetic insulation materials may not easily burn, however due to their lower fire-resistance, they must be protected by fire-retardants to meet strict building codes. Unfortunately, when exposed to fire (high temperatures) these complex chemical compounds will be released to air causing toxic pollution.
You have to take into account not only the cost of material but also the complexity of installation process (manpower and time). When making decision, please keep in mind the popular wisdom: What is initially cheap, at the end may become expensive”.
Many protagonists of eco-friendly lifestyle are inspired by the idea of recycling cargo shipping containers into habitable spaces. Most likely, owners of customized container houses are attracted by the idea of “small is beautiful”. They take advantage of the “out-of-the-box” solution, planning to settle somewhere far from the busy, hectic city life. Prospect of living surrounded by Mother Nature will probably inspire them (you) to adhere to the norms of “eco-friendly” lifestyle and all that comes with it (more nature, less pollution). Your choice!
Thermal Insulation of Customized Container Houses
Sidings of Customized Container Houses (walls and roof) are made from sandwich panels. These large building blocks consist of insulation material sandwiched between two sheets of pre-painted galvanized steel.
Most manufacturers offer a selection of different insulating materials – typically Rockwool, Polyurethane (PU) and Expanded Polystyrene (EPS). Some also advertise the availability of Phenolic Foam (PF)-based sandwich panels.4
PU Sandwich Wall Panel (Source: Baodu International Engineering Technology Co. Ltd en.baodu.com/
Sandwich panels come in three different thicknesses, the most typical is 50mm (approximately 2”), followed by 75mm (3”) and 100mm (4”) to accommodate more demanding climate zones (for extreme conditions you can even find 150mm (6”) panels).
Customer’s job is to select the suitable thickness of insulation panels and the preferred insulation material from the list provided by manufacturer. It’s as simple as that!
When it comes to floors, the most popular materials offered by manufacturers of Customized Container Houses are:
a) Plywood – Typically, about 20mm (0.8”) thick, not-treated panels are used as subfloor (note that it must be additionally insulated from weather elements to prevent absorption of moisture.
b) Cement Fibrolite Panel – it’s a composition of cement and wood fibers (cellulose).
c) MgO Panel – it’s mainly the composition of magnesium-oxide with cement.
Unless specifically required by weather conditions, such floor panels represent adequate thermal insulation barrier without any extra layer of traditional insulating materials. Obviously, they also include water-impermeable, rot and mold resistant bottom protection layer.
Practical Aspects of Installation of the Insulation Barrier
The blanket-type of insulation (fiberglass or mineral wool), due to its woolly nature and flexibility is probably the easiest to install on corrugated steel walls achieving continuous thermal barrier. Given the fact that the blanket insulation is not self-supporting, its installation will require some sort of accompanying structure.
The spray-type of insulation (preferably closed-cell) is easy to apply and offers almost perfectly continuous encapsulation of any object. Spray-foam will “effortlessly” shield uneven, irregular surfaces offering solution for corrugated steel. On the negative side -it is difficult (at least in DIY-approach) to make its outward surface flat and smooth, because expanding foam spreads out freely. That’s why, usually it will need some post-application trimming.
Spray Foam insulation (Right – professional application, Left– Possible shape when “flatness” is not needed (Source: SprayFoamUSA)
Big Styrofoam-type insulation panels can be easily secured to container’s walls by glue, so their installation is quite straightforward. Some manufacturers even offer rigid-insulation panels designed for corrugated surface (fitting rippled shape patterns of the wall). The only inconvenience is that you have to precisely cut the panels around openings (windows, doors, vents etc…) to eliminate any air-filled gaps (if any, you can then fill them by using spray-foam insulation).
Note that in general, thermal insulation materials do not create appealing to the eye, finish. They are also not robust enough and/or suitable to attach cabinets, wall decorations, to install electrical outlets…. So regardless of what kind of an insulating material is used, at the end, it will have to be covered by some traditional finish (drywall, wooden panels, plastic boards, ceramic tiles etc…).
Closed-cell, injection-molded EPS foam panels (Source: InSoFast)
What about sandwich panels?
They are available directly from manufacturers, so theoretically, can be used for insulation of cargo shipping container houses. They seem to be however quite impractical to use in such applications. Using metal-finished panels on corrugated metal walls you still end-up with metal walls, it will be more labor intensive (cutting panels to accommodate openings in the walls) and most likely costlier than traditional insulation.
How to insulate floors?
In most cases, the old plywood floors of cargo shipping containers will be removed. They are chemically treated (often heavily), and most likely deteriorated/damaged during the service in the transport industry.
In their new lives as habitable spaces, you can implement the same solutions as manufacturers of Customized Container Houses. It means very familiar plywood or cement-based subfloors (fibrolite or MgO panels). They are all available on the market either in retail or directly from manufacturers.
For obvious reasons (health) the plywood should not be treated so it’s bottom surface must be insulated from weather elements. But that’s not all – insects, rodents as well as potential exposure to abrasion and mechanical stress (stones, roots, ice…) require mechanically solid and durable protection like for example regular cement panels (often used as substrate in baths in traditional housing).
If necessary (justified by climate zone), you may also include an extra layer of thermal insulation to improve floor’s thermal performance.
The upper finish can be anything you would like to see and feel in your living quarters (hardwood, vinyl, ceramics etc…, Note that carpet is not suggested as it easily accumulates dirt and moisture.
Weak spots in thermal encapsulation
When it comes to traditional insulation, the most important part is the ceiling, because that’s where the warm air is drifting due to the natural convection and eventually escapes outdoors. That’s why when planning insulation of the cargo container house, the best performing (highest R-value), or thickest layer of insulation must be used for the ceiling.
Insulation layer is the most important part of the energy-efficiency strategy for the habitable space. But regardless of how good it is, insulation layer itself will not save all problems. Equally important is energy efficiency of “weak-spots” like windows, doors, vents as well as proper ventilation (dehumidification) of the space.