After her home burned in last year's Marshall fire, Melanie Glover returned to her charred garden in Superior's Sagamore neighborhood.
Glover and her husband, Matteo Rebeschini, weren't sure if they would rebuild after a panicked evacuation and the loss of their cat.
An odd sight shifted their thinking. The fire had melted four plastic flower pots aligned on a concrete patio, leaving behind pyramids of soil unscathed by a disaster that incinerated more than 1,000 homes in Boulder County.
"That made me think: Dirt doesn't burn," Glover said. "You can shape it, you can change it, you can form it into something — and it doesn't burn."
An increase in climate-driven wildfires has revived interest in one of humanity's oldest building materials: earthen blocks.
Archaeological records show people have made shelters from mud and dirt for at least 10,000 years through methods refined to build ancient structures like Mesa Verde and the Great Wall of China.
Experts now suggest similar techniques could help communities build more resilient neighborhoods.
Michele Barbato, a structural engineer and professor at the University of California Davis, said his research has found wildfires can even fortify the blocks, baking them into traditional bricks.
"They actually get better with fire," he said.
Barbato thinks the main barrier to wider adoption in the United States is more cultural than technical. After World War II, the construction industry learned to rely on mass-produced materials like wooden studs and drywall, losing the art of earthen masonry. Local building codes later cemented "stick-built homes" as the standard across the country, he said.
A down-to-earth home
Glover and Rebeschini never loved living in a home built to those standards.
Developers erected the Sagamore neighborhood in the 1990s next to an expanse of Colorado foothills. The couple tried to stop high winds from bleeding through the walls each winter, placing outlet covers over the electrical outlets.
"I affectionately call our previous home 'the tissue box,'" Glover said with a heavy dose of sarcasm.
After the fire, the couple started looking for a company to rebuild their home with earthen blocks. Glover found one driving Colorado State Highway 93 between Boulder and Golden. A hand-painted blue and yellow sign announced the location of Colorado Earth, which Glover quickly photographed and sent to her husband.
Lisa Morey, an engineer and architectural designer, founded the company in 2017 after studying earthen construction in New Zealand and writing a book about the techniques. She selected the site in Golden for its proximity to an active quarry, which produced clay-rich soil as a byproduct.
On a recent afternoon, Morey let the couple see how the company makes ecoBlocks, its branded name for compressed earth masonry units. The blocks are molded from raw dirt that’s the color and texture of a baseball infield. A set of hoppers sift the material onto conveyor belts, where it's mixed with crushed limestone and a small amount of water.
The final step is the most important: A hydraulic press crushes the material into solid blocks, which machinery files out onto a line of metal rollers. Workers stack the blocks on pallets to dry before they're trucked to building sites.
Morey said five families who lost homes in the Marshall fire are now under contract to rebuild with the blocks. None of them have received building permits yet, but she plans to submit designs for the Glover and Rebeschini home to the Town of Superior next week.
Something more solid and sustainable
The Marshall fire recovery has driven new interest in sustainable building techniques. To encourage more efficient homes, Colorado worked with Xcel Energy to offer discounts if property victims rebuild to different energy performance standards. The largest rebate of $37,500 is set aside for homes with Passive House certifications, a set of building criteria first developed in Europe.
Rebeschini and Glover considered Passive House but decided against it after learning about the amount of synthetic insulation and plastic tape often used in construction.
Earthen homes offered the couple a more natural approach to energy efficiency. Adobe-style walls absorb heat, which helps maintain a stable indoor temperature in the summer and winter, Morey said. She's run tests on a home her company helped build in Douglas County to confirm the benefit.
Morey thinks it's also critical to consider the climate impact of producing building materials in the first place. Those "embodied emissions" are one reason a recent estimate found the construction industry accounts for nearly 40 percent of global climate-warming gases. Blocks made from local dirt could be one way to cut the impact.
"During this whole process, there's no heat applied. That's important because it takes a lot of energy to fire a brick, and that's not necessary for the blocks we produce," Morey said.
Another question is the cost. Glover and Rebeschini expect to rebuild their home for about $250 per square foot. Last February, the Colorado Association of Home Builders estimated families would pay between $260 and $300 per square foot to rebuild in the burn area.
But the couple only achieved the lower price tag by agreeing to serve as their own general contractor. Rebeschini said the extra effort is more than worth it after the wildfire destroyed his family's sense of security. He can’t imagine moving back into a house unprepared for the next disaster.
"No matter where you are today, you're never safe. We are building to maximize the sense of safety and comfort inside the home," Rebeschini said.
