Building and Construction, Operations, Uncategorized, V9I2

Sheds to Tiny Houses: Rethinking the Design

(Photo courtesy of Edho Pratama on Unsplash)

We all know that choosing the right materials is crucial to the quality of any final product. But sometimes we overlook the interaction of these materials with the design.

Cards on the table: I’m the sales guy for an insulation product. Our core market is in residential and commercial construction, and, therefore, I usually talk with architects and contractors. 

But recently we have found interest—really a demand—from partners in the shed, barn, and tiny house industries. This is why during the last few months, I have visited many shed builders and manufacturers of tiny homes.

The demand for tiny homes keeps going through the roof, and smart shed builders are jumping into this new market. I’ve noticed that most manufacturers of tiny houses started their businesses as shed builders. 

These tiny houses are used for remote working, reading, yoga, or hobbies. The space needs to be comfortable year-round and in all kinds of weather. The livable shed will need to stay pleasant and protect against heat, cold, and condensation. 

In other words, the shed needs to be “upgraded” to meet the demands of a tiny house.

Building regulations and requirements for sheds and tiny houses differ from state to state and county to county—even from town to town. But most building regulations don’t require a permit for a shed or a tiny house when the dimensions are limited. 

For instance, in North Carolina where I live, no permit or inspection is required for constructions under 12 by 12. But even when the building code doesn’t apply, it is advisable to follow the provisions in the International Residential Code. 

Document ICC 2018 Appendix Q (https://codes.iccsafe.org/content/IRC2018P5/appendix-q-tiny-houses) contains guidelines (not mandatory unless specifically referenced by your local building code) for features in tiny houses such as compact stairs, including handrails and headroom, ladders, reduced ceiling heights in lofts, plus guards, emergency escapes, and rescue opening requirements for lofts.

As I’ve noted, most manufacturers of tiny houses started their businesses by building sheds and barns, and the transition into manufacturing tiny houses is natural. The construction of tiny homes derives directly from the experience and knowledge needed to build sheds. 

The owners of a tiny house will not only spend much more time in it than they would spend in a shed, but they also have different expectations about the design and construction, strength and durability, and energy efficiency. 

That’s why the switch from building sheds to constructing tiny houses requires re-thinking the design. It might even need some architectural research. For example, a different roof structure can make a huge positive impact to keep the climate of the tiny home comfortable. 

A few years ago, a study was funded by the U.S. Department of Energy and conducted by the Oak Ridge National Laboratory to document energy savings of metal versus asphalt shingle roofs. Scientists compared the insulation effect of an asphalt shingle roof to that of a metal roof. Testing was done in the field with real roofs. 

The asphalt shingles were nailed directly on the roof OSB boards with no air space underneath. The metal roof was attached to a batten structure on the OSB boards covered with a reflective underlayment that allowed for airflow underneath the metal panels. 

The results were astonishing! The metal roof had a 45 percent reduction in heat flow compared to the shingle roof. About 15 percent of that reduction was attributed to the emissivity of the underlayment, and an additional 30 percent of the heat flow reduction was due to the above-sheathing ventilation. 

I spoke with Gary Manlove at JBA Consulting, who was one of the authors of the article about the Oak Ridge National Laboratory research (A Study of the Energy-Saving Potential of Metal Roofs Incorporating Dynamic Insulation Systems By Kaushik Biswas, Ph.D.; William Miller, Ph.D.; Scott Kriner; Gary Manlove—https://web.ornl.gov/sci/buildings/conf-archive/2013%20B12%20papers/084-Biswas.pdf).

Gary confirmed that, in general, the use of a reflective insulation material in combination with some airflow (above-sheathing ventilation) under a metal roof is a construction that will keep the shed/tiny house cooler during the hot summer than a shingle roof containing asphalt shingles on OSB. The use of reflective materials will lower the heat build-up and will keep the structure cooler. 

What’s more, creating an air space under a metal roofing system will increase energy savings during both the summer and winter months. In cool or cold weather conditions, the study indicated that direct-nailed asphalt shingle roofs had significantly larger heat loss than attics with metal panels and above-sheathing ventilation. This is because the air gap serves as an insulating layer.

The study results have been corroborated by Florida Solar Energy Center and accepted by the ASHRAE (The American Society of Heating, Refrigerating and Air-Conditioning Engineers) SSPC 90.1 subcommittee. 

This example shows that noticeable insulation improvements result from a combination of both insulation materials as well as design. 

Again, many designs of tiny houses are largely based on original shed designs and the general practice is to just add some insulation material. In most cases, the insulation material is stapled or sprayed to the interior ceiling and walls. 

As an industry, we are always looking for materials that are affordable, easy to work with, and can be installed quickly. But sometimes we need to overcome additional issues. 

When it comes to insulation, we may be dealing with very limited space, weight restrictions, or the need to boost the R-value. These requirements will determine your best choice for insulation material. 

Every material has a material thermal resistance R-value, regardless of how it is used. To determine this intrinsic R-value, the industry uses ASTM C518, Standard Test Method for Steady-State Thermal Transmission. This test solely measures the resistance to heat flow. R-values from ASTM C518 are based exclusively on a material’s capacity to absorb energy/heat.

But in addition to the intrinsic R-value, insulation products may use their surroundings to boost their insulative capacity. 

Standard Test Method ASTM C1363: Thermal Performance of Building Materials and Envelope Assemblies measures the R-value when the product is incorporated into an assembly. 

Building codes require R-values for walls and roofs. These R-value requirements are based on the thermal performance of the entire assembly (ASTM C1363) and not just on the R-value of the insulation product alone. 

For example, take a wall assembly that includes an air gap. Air is an excellent insulator. That is why even the air gap has an R-value because it prevents the conduction of heat. 

Please see the chart above for code-compliant residential wall construction and how all materials and the air gap contribute to the overall R-value. (R-Value 15.82)

Not all insulation materials are designed to absorb heat. Insulation materials with a shiny aluminum layer are designed primarily to reflect radiant and convection heat. They have very low emissivity. 

Those insulation materials will not absorb heat—instead, they reflect heat. Think about it like the fabric of an umbrella. The fabric of an umbrella isn’t there to absorb the rain, rather it repels the rain to keep you dry and comfortable.

The key is that all materials in the construction play a role in the overall R-value of the assembly. It is not only the insulation material that counts. 

Exterior cladding and interior finishing products are also part of the same equation, as well as how these materials interact. 

As shown in the chart, the contribution of an air gap can be considerable (R 2.84). Therefore, it is not only the choice of insulation material but also the design and installation that are important. 

This justifies a closer look into the options that are available to make the tiny house comfortable. Unfortunately, I see many shed builders use radiant aluminum-coated insulation sheets and staple them directly to the ceiling or roof panels and walls. 

In my experience, things seem to work much better when used as intended.

Finally, consider your design and be aware of some structural design features that are required by the building code. There is always a reason why it is in the code. 

For instance, use “nailers” in the walls for interior sheathing, like drywall. These studs and rafters provide a nailing surface to attach the interior sheathing. All sheathing, on the inside and out, should always be connected to framing for fire protection and strength.

I hope that these observations will give you some food for thought. In short, there are several options available to reach your target. Your choice of material is not the only crucial thing, your choice of design can be just as critical.

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