Gutex-Wrapped Tiny House in Arkansas

Gutex-Wrapped Tiny House in Arkansas

Experiences Using Passive House-Supportive Products on Our Tiny House on Wheels

This guest article was written by Rachel and Donovan, the good folks behind Go check them out to read more about their experience.

Our Tiny Journey

Although it’s technically “tiny,” our Tiny House on Wheels (THOW) has some monumental goals. We intend for it to serve as both a model home for healthy people and a healthy planet, and also as a means to implement a low-impact, minimalist lifestyle for ourselves. Oh yeah—and we like to be comfortable! In the extreme (and increasingly unpredictable) weather of the Arkansas Ozarks, that itself is a large task. Donovan was trained as a Passive House Consultant in 2016, so toward our purposes, we are implementing Passive House design and using products from companies like 475 that provide materials for high-performance building.

Our premier tiny house, Juniper—so named for the native eastern red cedar, or juniper, siding it will have—is designed to include an air-tight envelope; full-scale ERV; passive solar window strategy using R7 to R9 casement and fixed windows; grid-tied solar PV system; earth plaster interior wall; solar thermal hot water; on-site rainwater catchment and gray water recycling; compost toilet; and siding that is locally sourced and milled.

So you know it's local
Milling down the wood
Using strips of Gutex on the rafters. We’d recommend using denser Gutex boards if you go this route.

We recently completed the installation of the Gutex weather-barrier insulation boards to break the thermal bridging in the wall and roof framing. (See photo above) We are also utilizing the skills and expertise of local tradespeople, glass artists, and woodworkers, including family members, neighbors, and others in our community.

Besides being value-driven, our decision to go tiny is also, like that of many “tiny housers,” a practical choice. Some have questioned why we’d spend the labor and expense on highly insulating materials and techniques for such a small space: “It’s not that big; it won’t take much to heat or cool it.” To which we respond, “This is the Ozarks! We’ve lived in homes under 500 square feet with cold, drafty single-digit winter days, summer temps soaring into the hundreds for weeks, and moldy basements, and by golly, we’re sick of it!”—Or something to that effect. In fact, the intensity of our southern summers is one reason we chose to use Gutex, which has a specific heat capacity superior to that of foam. But there’s more to that decision.

Reducing Plastic Is Fantastic

One reason we chose Gutex for our tiny house is to break the thermal bridging using a more space-conservative method than double stud framing or I-joists would allow. However, our primary reason for choosing Gutex was the lack of alternatives for (petroleum-based) foam. We debated the sustainable viability of using a product made across-sea in Germany and decided that creating a demand for a foam-free alternative outweighed the embodied energy of shipping the product to us. And, in fact, the embodied energy of the Gutex wood fiberboard turns out to be negative, even after accounting for transportation. The modern Zero Waste movement has significantly influenced us to seek trash-free and low-embodied-energy products for our homes and businesses. As nature-lovers and sensitive people, thinking of the end-life of the house’s components (even though we envision our tiny long outlasting us!) and working with non-toxic products is vital. So using foam products, even in our exterior walls, was not an appealing option.

A confession: we did use reclaimed foam board (from local chicken houses) for our site-build SIP floor to break the thermal bridging from the steel frame trailer. We initially felt good about implementing a material that would otherwise go to the landfill, and the price of the reclaimed foam was right. However, the experience of cleaning, patching, and cutting the boards to size, inhaling the plastic off-gassing as we cut them with power-saws, and getting our sweaty skin and outdoor area plastered with irritating foam bits made us rethink our decision. We estimate that the time spent on prepping the foam boards alone would pay for the extra cost of using Gutex for the subfloor, which we plan to do for our next tiny house.

The foam SIP experience provided an informative contrast to working with Gutex; it was our hands-on experience with Gutex that really sold us on the product. Unlike the issues we had with foam board micro-trash, the Gutex is Nature-Plus certified, and the bits and pieces that float around the job site will eventually break down without causing harm. We’re even collecting the scraps to use as a carbon source in our compost toilet!

Gutex MULTITHERM 60 goes up on 2x studs, stacking tongue-and-groove to create continuous insulation
Battons are applied to the exterior of the Gutex to create a drainage plain

We’ve also found working with the product to be a relatively pleasant experience. The approximately 312 by 212-foot panels are easy for most body types to lift and move around the site. The tongue-and-groove edges fit together beautifully to create a rain and wind-resistant barrier. Where we had to cut odd pieces to fit and lost a tongue or groove, we primed and taped the seams with TESCON VANA weather tape. The primer allows for the adherence of the tape to the otherwise fibrous surface of the Gutex. The boards shed particles when cut but we found that hooking the Shop-Vac hose to the table saw while cutting the Gutex greatly reduced this.

I know what you’re thinking: “But what about the shear strength?” To reduce the weight of Juniper, we omitted the plywood on the outside and will glue and nail a beautiful, formaldehyde-free birch plywood (half-inch) on the inside to provide shear strength for the framing, which will double as the finished wall. By eliminating the outside plywood, we reduced the weight by approximately 1,050 pounds, allowing for the Gutex to fit within the weight “budget” of our trailer’s axles (which are rated for carrying 21,000 pounds).

Ozarkian Taping Tips

A close-up of the tongue-and-groove in action
Showing off Ozarkian taping moves to apply EXTOSEAL ENCORS to the window sill using a Pressfix application tool
Because Gutex is a fiberous surface, use TESCON Primer RP to prime the surface prior to tape application

After completing the Gutex installation, we hung and tape-sealed (after priming) the windows of the tiny house. Although this summer has been easy on us overall, we’ve dealt with several days in the hundreds, which unfortunately came while we worked on the south side of the house completing the weather-taping. Turns out hot tape, particularly the butyl-acrylic EXTOSEAL ENCORS sill tape, can be tricky to work with, but the simple solution was to tape in the early mornings or evenings.

The next step was attaching battens over the Gutex to form the rain screen. The battens were cut from the scrap boards left over from the juniper trees that were milled for the siding. This conserves resources and puts to use the advantages of red cedar that make it a great choice for exteriors: it’s a stable wood, with insect- and water-resistant properties.

Tools For Building a Sustainable Future

SketchUp has proven helpful for determining design elements, such as when “trying on” the siding before making a final decision. Donovan also used WUFI energy modeling software for selecting the Solar Heat Gain Coefficient, thermal value and quantity of windows, and the thermal value of the walls, roof, and floor. The components he modeled were 238” (60mm), R8.7 Gutex for reducing the thermal bridging on the studs and joists; 2x6 walls with R23 Roxul; R40 dense-packed cellulose roof; and R30 reclaimed EPS foam board floor. The thermal envelope is very challenging to balance, again, due to the limitations of width and height of a THOW!

High performance means great planning
Trial and error is best done in pixel form

Tiny Happy People

Overall, our first experience using Passive House products and methods has been satisfying on many levels. It is empowering to utilize tools to build a more healthy and sustainable world, and to build a home that will be able to stand up to our ever-changing climate. If you’d like more details about our build or want to more closely follow our progress, check out our blog:

Products we’ve used from 475 to date: