We built this earthbag roundhouse in 2010 as part of an earthbag workshop in Thailand, and finished it later that summer. Roundhouses are perhaps the simplest, fastest, easiest earthbag structure to build. We’re extremely pleased with the results, especially in terms of strength and cost. This is one of the strongest structures I’ve ever worked on in my 30-plus year construction career. The main impression is one of incredible fortresslike strength - massive walls with no sway. I’m sure it could easily withstand a direct hit by a speeding vehicle. This is no exaggeration. There’s been at least one incident where a drunk driver hit an earthbag wall and only chipped the plaster. (The vehicle was totaled.) Earthbags also excel at withstanding floods, hurricanes, tornadoes and earthquakes. Engineered plans are now available for whatever conditions you face. Earthbags are even bullet resistant, as explained in our highly popular blog post where compressed earth withstood 50 cal “BMG” 661 grain Full Metal Jacket rounds. Bullet Resistance of Compressed Earth
The other key advantage of earthbag is cost. For our roundhouse, we wanted things to look nice, of course, but we didn't want to spend a fortune. The final cost came out to $11.50/square foot. Most stick-built houses are $100/sq. ft. and up, so this roundhouse demonstrates how anyone can build their own home even on a very tight budget. We used a few basic, low cost methods to class up the roundhouse: rounded window and door openings (free), nice colors (no extra cost), curved bathroom wall and buttress (no extra cost to create curves), exposed wood and thatch roof (dirt cheap), earthen plaster on the interior (really dirt cheap), and lots of beautiful old windows for views, ventilation and to add a sense of spaciousness. In summary, build small -- just what you need, use simple shapes, pay with cash, and add on later if needed.
Basic project information:
18’ exterior diameter; 15’ interior diameter; 177 sq. ft. interior floor space; total cost of materials: $2,045, which is about $11.50/square foot
The following instructions assume you have cleared and leveled the site, removed topsoil, positioned fill soil around the building site to minimize work, dug a trench to stable subsoil, buried any utilities, put about 12” of gravel in the trench, and added a center pole with stringline to measure the radius. Bags or tubes can be used. We demonstrate bags, because they’re often available recycled for very low cost. My YouTube Channel has short video clips that show each step of construction.
Step 1: Earthbag Foundation
Earthbag foundations – gravel-filled bags or stabilized bags – offer many advantages over reinforced concrete foundations and work well with many types of sustainable buildings. In particular, they are low-cost, fast and easy to build, require no cement (a major expense and cause of global climate change), and require no forms or expensive equipment. In cold climates you can use lava rock or pumice to create an insulated foundation. This one simple step can save you thousands of dollars over building with concrete, and cut your energy costs.
Typical earthbag foundations are made with poly bags (double-bagged for strength) filled with gravel. Aggregates are preferred for foundations because they will readily drain away any moisture and prevent wicking into the wall system. Some prefer to use stabilized soil in earthbag foundations, seeing it as a longer lasting solution. The jury is still out, but it appears poly bags kept out of sunlight can last hundreds of years, so gravel-filled bags should last at least a lifetime.
Simply fill the bags in place with gravel. Stitch the ends closed or fold the bag end over. Butt each bag tight against the previous bag. Tamp the bags flat after each course is complete. Add two strands of 4-point barbed wire between each course. Add courses of gravel-filled bags until you’re at least 6” above the risk of moisture damage.