Building an Ecological Tiny House with Natural Materials

People all over the world have been building ecological tiny homes and other structures with natural materials throughout human history. Here, we dig into the differences between conventional and more ecological building materials and discuss three natural building modalities to consider when building a tiny house: 

• Rammed earth
• Hempcrete
• Cordwood

Sustainability of building materials: conventional vs. natural building

When assessing the sustainability of conventional and natural building, one must take the embodied energy of methods and materials used into account. According to the Sustainable Construction Glossary, embodied energy “is the total of all the energy consumed in the processes associated with the production of the materials and products that go into a building or structure”.

Image source: Etool

Industrial or “conventional” buildings rely on the embodied energy of fossil fuels, machines, and non-renewable and toxic materials for their construction and operation. Vast quantities of plastic, paper, water, and other resources are consumed and thrown to waste throughout the building process. 

Even “green buildings” are accomplished using highly industrial and technical methods, despite their energy efficient benefits. The materials used to construct green buildings are often produced in factories using mechanizations and systems that are not environmentally friendly. At this point, calling a building “green” really only refers to its energy use and efficiency once it’s built, and doesn’t take the building process into account at all. 

Natural building, on the other hand, is an ecology of construction with sustainability at its core. Often, the materials used in natural building are renewable, non-toxic, and are local to the building site, including local timber and natural paints. When you look at the total lifespan of the building, you’ll usually find that natural buildings have a much lower ecological footprint than “green” or “conventional” buildings.

Image source: Centre for Building Performance Research

Choosing the right natural materials for your location: thermal mass and insulative value

When considering what natural materials to use when building your tiny (or not-so-tiny) house, it’s important to consider your location. Depending on your average day and nighttime temperatures, you’ll want to use materials that are high in thermal mass, are highly insulative, or a combination of both.

What is thermal mass?

Thermal mass is determined by how long and how effectively a given material will hold heat. Take rocks, for example: A rock will heat up when placed in the sun; then, when you bring that rock inside, it will emit the heat that it absorbed for a long period of time. Similarly, if it’s a cold night and you go to sit on a rock, it’ll extract the heat from your body…and your bootie will feel cold! Something less dense, like a plastic lawn chair, will absorb some heat in the sun, but very quickly cool down when you bring it inside; the rock has higher thermal mass than the lawn chair. 

This same process applies to buildings. Basically, materials with a high thermal mass can help keep a space cooler during the day and warmer during the night if they’re exposed to sunlight. In places where there’s a big fluctuation between day and nighttime temperatures, like the desert Southwest, you’ll want to build using high thermal mass materials to help regulate these varying temperatures.

Image source: Green Passive Solar Magazine

Insulative materials and R-value

If you live in a place like Alaska, Vermont, Wisconsin, or anywhere with cold winters, then you should build with insulative materials to reduce heat loss from your tiny home. Likewise, if you live in South Florida or another hot place, and you plan to run air conditioning, you’ll want to have a good amount of insulation to keep the cool in and the heat out. 

You can understand how insulative a material is by finding out its R-value. According to the Building Performance Institute, Inc., “R-value itself is a measurement, a rating, which corresponds to a material’s thermal resistance (the ability to resist heat transfer through conduction). The higher the R-value, the greater resistance to heat transfer.” Meaning, the higher the R-value, the more insulative a material will be. 

R-values per inch of some natural materials:

• Adobe: 0.2 – 0.3
• Strawbale: 0.94 – 2.38
• Hempcrete: 2 – 3.5

Natural building modality #1: Rammed Earth

Building with rammed earth

Rammed earth is an ancient building modality that’s been practiced for thousands of years. In fact, the Great Wall of China was partially constructed using this technique. Historically, wooden wall forms were constructed and then soil was tamped, by hand, into the forms until they hardened, producing sturdy buildings that have stood the test of time.

Image source: Green Technology Project by Nicole McDonald

Ideally, soil for rammed earth construction is extracted directly from the building site. In order to do this, you need to have the right soil make-up on location. Before being used for rammed earth construction, the soil is mixed with some sort of stabilizer. Historically, those stabilizers have included blood, urine, fibers, lime, or animal hair. Nowadays, the stabilizer is typically cement. Rammed earth walls can be incredibly strong and load bearing, meaning that the roof can bear directly onto the walls without needing any sort of wooden skeleton to support it.

Image source: Rui André Silva

In this day and age, forms are built and then pneumatic tampers are used to ram the soil-cement mix into the forms. Yay for technology! You can even make blocks off-site with a Compressed Earth Block (CEB) machine, if desired.

Pros and cons of rammed earth construction

• Pros

  • Thermal mass
  • Permitable
  • Uses on-site soil
  • Materials are less expensive

• Cons

  • Not insulative
  • Expensive if not doing it yourself
  • Labor costs can be very high

Check out the video below to learn about more of the pros and cons of rammed earth construction.

Natural building modality #2: Hempcrete

History of Hempcrete

One of the earliest applications of hempcrete was found in France at a bridge abutment from the 6th century, and it’s still intact today! Now we’re seeing a resurgence of hempcrete materials being used to build strong, non-toxic tiny (and not-so-tiny) homes.

Image source: Tiny Hemp Houses

To make hempcrete, you simply combine industrial hemp stalks, lime (hydrated or quicklime), and water. What happens is that the silica in the hemp shiv (the woody, inner core of the stalk) allows for a strong bond with lime to create a concrete-like material (hence the name hempcrete). Similar to the process of making concrete, you simply mix the wet materials and then allow them to dry in place. It’s possible to make blocks and stack them, or use forms to build up hempcrete walls.

Image source: The Hemp Mag

Pros and cons of hempcrete construction:

• Pros

  • Insulative – R 2.5-3 per inch
  • Better than wood chips
  • Highly renewable material
  • Mold resistant

• Cons

  • Uses industrial processes
  • Not structural
  • Relatively expensive

Check out the video below to learn more about the pros and cons of hempcrete construction.

Natural building modality #3: Cordwood

What is cordwood?

Cordwood structures date back nearly a thousand years, but they became more accessible to lay people in the 1800s, when saws were more readily available. This natural building technique involves using pieces of logs, typically 16 – 18 inches long, and surrounding and encasing them in masonry to construct beautiful, unique wall systems.

Image source: Llyod Khan

The wood used for cordwood construction should ideally be rot-resistant softwood, like western red cedar or cypress, and can be round or split. To construct a cordwood wall, you’ll first add a layer of masonry or cob to both ends of your logs. Then, in the middle layer, you’ll add wood chips or some other light material and coat it in clay or lime to create a thermal block. We recommend kiln drying your wood to prevent shrinking and cracking in masonry.

Image source: Bennett House Project

Pros and cons of cordwood construction

• Pros

  • Can use small pieces of wood or waste wood
  • Fun to do with a group
  • Relatively well insulated
  • Carbon sequestration

• Cons

  • Movement of wood can cause cracks and crumbling
  • End grain of wood exposed
  • Extremely labor intensive

Check out the video below to learn more about the pros and cons of cordwood construction.

Learn to build your own ecological tiny house

Are you interested in building your own tiny (or not-so-tiny) house with natural materials? Understanding the environmental impacts of your build and how to intentionally work with Earth’s bounty can potentially save you lots of time, money, and energy. In our  Online Tiny House Academy, we offer concrete ways to reduce your ecological footprint through smart design and sourcing. Learn more about the online class and sign up for the waitlist to be notified when class opens, plus receive special offers.