Are EPS panels a good idea for insulation? Let’s look at one system: InSoFast

With all the tiny homes on the market, there’s one that we never thought would be super-comfortable: a shipping container.  However, a new insulation system has innovated simple, successful methods of insulation and waterproofing this notoriously difficult module.  In this article, we look at the design features of one company’s panels, as well as the drawbacks of the material used.

InSoFast is a company that does for insulation what their name says: it’s installed fast.  They have a variety of products to provide insulation for common and difficult living spaces: all kinds of regular homes, as well as basements, concrete block buildings, and shipping containers.  Looking at this last one, shipping containers seem like a solid choice for a home: steel, somewhat uniform, water resistant (if it’s in good condition).  But the corrugated walls present a lot of challenges.  How do you seal windows and doors?  How do you insulate it?  How do you run electrical and plumbing?  How do you attach drywall and siding?  The company has addressed each of these with innovative designs and methods.  The principles behind their brackets and insulation system support good new home design:

• Prevention of thermal bridging, which is the transfer of heat or cold by structural elements (the corrugated steel) to the inside or outside

• Continuous, homogenous insulation (unlike spray foam or batt insulation) prevents condensation, because no steel surface will remain uninsulated.  The panels have tongue-and-groove interlocking edges.

• Shaped insulated studs can be applied to the interior with adhesive so that random holes in the container for attaching studs is avoided. 

The idea and designs are very useful.  The insulation panels are made of Injection-molded EPS (expanded polystyrene). In our article on wall insulation for your basement, we list the reasons that EPS is one of the best foam insulations you can use for a basement (or shipping container), even better than XPS (extruded polystyrene, because of its low water absorption, some vapor permeance, and low loss of R-value over time.  Read on to the end to make your final decision, though, because styrene and its additives have potential to affect your health.

Here are the answers InSoFast has devised for shipping container use:

• How to install and seal (flash) windows and doors (areas most prone to water intrusion in homes) is shown in these videos and tutorials.

• How to run electrical wiring: The panels have integrated channels 16” on center vertically and 24” on center horizontally; this page shows installation of wiring and electrical boxes. 

• Plumbing presents probably the biggest challenge with these insulating panels, because pipes should be placed on the interior (not behind) the insulated surfaces to avoid freezing.  To avoid having to install 2x4 walls to conceal it, plumbing can be placed inside separating walls (cross-walls) in the container and/or one end of the container can be built out with a stud wall over the insulation, in which the plumbing can be placed.  This page gives some tips and solutions. 

• How to attach drywall/paneling: Shaped insulated studs (made of polypropylene) are glued to the inside of the container using adhesive. (video).  

• The industrial adhesives used are convenient and strong; Loctite’s 3X Stronger formula is designed to cure 3 times stronger than average solvent-based varieties, and a single bead can outperform screws spaced 6 inches apart (wow!).  Loctite PL Premium has the GREENGUARD Certification, which is given to products with low chemical emissions.  Since one of the goals of the shipping container home is to be airtight and thereby more energy-efficient, it’s important to use products that have low emissions for your body’s health. (Panel Adhesives)

This testimonial from a DIYer is a positive one.  She is a tiny home owner and also an aerospace engineer who, after insulating and finishing her own shipping container, is considering changing careers to buying and outfitting containers for others as tiny homes.

Of course, there are downsides to using InSoFast:

• Cutting foam panels with power saws makes A LOT of dust and plastic pollution.  Working with this material and a powertool should only be done using a respirator.

• It may or may not be less expensive to build out the interior in a traditional way with 2x4’s and fiberglass insulation, but the time-saving features of InSoFast would be competitive.

• Although the level of insulation is fine for the US South and mid-latitude, the insulation would not be enough for northern climates . Here is a table showing the varying R-Values of their different products (thinnest to thickest panels).  Climate zones 5-8 in the US require R49-R60 on the roof or attic, and R25-R30 on the floor. (A Guide to Exterior Insulation: Breaking Down R-Values)

Source: Listing and Technical Evaluation Report

• Flammability: EPS by itself is flammable, but like most EPS that is manufactured for building insulation purposes, it has been treated with Fire Retardant Additives (FRA’s).  The specific fire retardant(s) are not named (trade secret) but typically a brominated styrene butadiene copolymer, also known as Poly FR (for fire retardant). (Flame Retardants in Insulation)  These can break down into at least 76 smaller byproducts, which many of these byproducts were found in the environment around electronic waste recycling facilities in China.  Exposure to relatively low levels of these byproducts resulted in developmental toxicity in laboratory studies. (Supposedly “safe” flame retardants become more toxic when they break down)

• Polystyrene is difficult to recycle so it usually is not recycled.  In the open environment or uncovered landfills, sunlight, wind and water will break it up into small pieces, allowing it to blow in the wind and be very difficult to collect, eventually ending up in farmland, rivers and the ocean.  The plastic itself does not degrade, so it’s not “decomposing”.  (The Problems with Expanded Polystyrene (a.k.a. EPS or Plastic Foam)  For these reasons, if you decide to build/insulate using InSoFast panels or other EPS foam, we strongly advise not leaving them uncovered and exposed to light (even uncovered inside) for very long.  Get siding and wallcoverings over them quickly to minimize material breakdown.

• Among styrene manufacturing workers, there is an increased probability of rare leukemia and nasal cancers.  In 2018, styrene was upgraded from possibly carcinogenic to probably carcinogenic for humans by the WHO. (After 40 years in limbo: Styrene is probably carcinogenic)

Are InSoFast products (or EPS foamboard in general) right for your home?  It’s quite a good design with a material that has health drawbacks, not only for your home but also in the broader picture of how styrene manufacturing affects others and the environment.  Like all the other decisions you make when building or renovating, careful planning and research makes all the difference.

Photo by Jens Behrmann on Unsplash