Last Updated: Oct 16, 2021
In the small town of Nebaj, about six hours north of Guatemala City in Guatemala, Elba Méndez and her family have preserved the country’s vernacular architecture form by building a round home from a mixture of cob and cordwood. “We wanted to build an earthen home because they’re so much nicer than the block and cement homes everyone is building around town,” she says. “We also wanted to make a round home because no one else in town has a circular house.”
Building in the round has other virtues, particularly in a country with more than 30 volcanoes (several of them active), and is prone to earthquakes. “The circular structure offers superior strength,” says Méndez. “Whereas traditional adobe homes tend to crack around the corners, our cob home has settled and has no structural cracks or issues. Also, while our home only has three rooms [roughly 550 square feet], the circular shape allows us to easily move between the bedroom, kitchen, and living room.”
From Africa to Asia to the Americas, round homes are considered one of the oldest forms of shelter. The tipi, hogan, and igloo of North America’s indigenous peoples—as well as the Mongolian yurt and wattle-and-daub round homes on the British Isles—are just a few examples of round homes built by diverse groups.
While modern-day construction is dominated by straight lines, right angles, and tight geometric patterns, our ancestors modeled their shelter off of circular patterns common in nature. From eggs to tree trunks to bird nests to caves, the natural shelters of wildlife are almost always round in shape. Early people modeled their home styles to reflect what they found in the natural world.
More recently, the growth of sustainable construction practices and natural building methods such as cob, rammed earth, and adobe has led to a renewed interest in round homes. Besides being uniquely aesthetic, round homes offer three distinct sustainability advantages:
Take a sheet of paper and try to make it stand on end on a flat table. You’ll find it’s impossible to make the paper stand upright while placed in a flat line. By curving that sheet of paper into an “S” shape, however, extra strength is added, and the paper can stay erect. Straight lines in architecture certainly make it easier for quick and streamlined building practices. However, the straight line is widely considered to be less structurally resistant than curved walls.
The curved walls of a round house offer extra strength for external pressure, which helps make the walls much more resistant to earthquakes. The walls of a round house have dozens of interconnected points, providing structural flexibility and strength. Because these homes are more aerodynamic, they are much more resistant to hurricanes and strong winds.
Examples of straight lines are rare in the natural world. Nature seems to prioritize twists and turns and circular patterns. A round home, then, offers a natural advantage when designing a biophilic home that blends in with the natural world.
Circular homes don't have corners that end up gathering dust. Generally speaking, round homes allow for more efficient use of space, and creative interior design with natural flow between spaces. As an added benefit, round homes are generally less expensive to build. The lack of complicated structures and multiple surfaces can require up to 20 percent fewer materials per square foot of construction, thus driving down the final cost.
Round homes are more energy efficient than their rectangular counterparts. Why? Because they have less surface area relative to floor space, there is less wall exposure to the exterior elements. This allows homeowners to invest in high-efficiency insulation and high performance windows in strategic wall spaces to maximize the energy efficiency and thermal performance of the home.
Because round homes are naturally aerodynamic, they’re less drafty, thus further increasing the homes’ comfort and thermal performance. In addition, round homes use fewer materials. In geometric terms, the circle has the shortest boundary relative to its area, thus requiring less material for overall home construction—which gives round homes a lower embodied energy rating than other homes.
The Deltec Innovation Center, a 1,500-square-foot Net-Zero Model Home in Mars Hill, North Carolina, is one example of a sustainable round home. The model home has reduced the exterior surface area for the same interior square footage, resulting in less total heat loss and lower heating and cooling demand.
According to Leigha Dickens, Deltec’s Green Building and Sustainability Manager, “The radial design of our trusses, meaning they radiate from a center point like spokes on a bicycle wheel, adds considerable strength to the structure, while the round shape helps reduce wind pressure. Both of those features contribute to an incredibly strong structure, and we specialize in high wind design.” With global climate change increasing the likelihood of strong hurricanes and other extreme weather events, stronger structures are essential for a resilient home.
The Innovation Center’s round model home incorporates other sustainability elements, including passive solar design, super-insulation with R-values and window performance values well above the local energy code, air-tight construction, and fresh air ventilation. The home has high-efficiency heating and cooling, hot water, lights, and appliances. The all-electric home is paired with a grid-tied solar array sized to offset the home’s yearly energy use through a net-metered system.
The model’s structural shell is constructed indoors in a facility that uses renewable energy. Together with a 5.12 kW grid-tied solar array, all of these sustainability features allow the center to achieve Net Zero energy status.
The town of Nebaj averages close to 60 inches of rain each year and many of the town’s new cement homes have severe problems with humidity and mold. “Earth homes are cooler during the day and warmer at night and don’t have problems with excess humidity,” says Méndez. “We also knew that adobe homes are not exactly earthquake resistant, so we learned about cob construction at a natural building workshop and decided to go that route.”
Cob construction, an ancient building technique, is similar to the traditional adobe construction in that it uses a combination of moderate clay soils and straw. Unlike adobe, however, cob is considerably stronger. Cob’s clay and sand combination give the walls good compression strength, whereas the use of straw or other fiber-like material offers optimum tensile strength.
The dirt and straw are mixed with water, then placed on top of a rock stem wall that protects the wall from moisture at ground level. Because the mixture is not first made into bricks (like traditional adobe), there are no mortar joints, essentially making the cob wall one solid structure, similar to poured cement.
Initially, Mendez was worried about the work required to mix the cob for her new round house, she says, “so we were able to get 150 pieces of cedar cordwood that we incorporated into the walls of the home. This reduced the amount of cob we had to mix. It also offered a unique final look to the home once we finished the natural plasters and varnished the pieces of wood.”
The cob/cordwood round house incorporates up-cycled materials. “The post and beam structure for the roof was sourced from a wood house that was being torn down for a more modern cement home,” Méndez says. “I also found broken glass that we used for making small, circular windows to maximize the amount of natural light. Around the wood-framed windows, we added blue and green wine bottles that flood the home with unique light during the early morning.”
Our ancestors might have understood one quality of a round home that’s a little less obvious than reduced energy use and clever space allocation: the powerful and natural movement of air and sound. As David Raitt, a yurt builder has said: “Circular living provides a balance of looking inward and outward, looking out at the natural environment and surroundings but then coming in again to the self and the hearth.” The curve appeal of round homes today comes in the form of a house of the future, based on the past.
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.