Note: If you’re new to earthbag building, first read the introductory Step-by-Step Earthbag Building Instructable and How to Build an Earthbag Roundhouse . Also, my new Earthbag Building Guide and Earthbag Building DVD are now available.
We built this earthbag dome at our home in Thailand for Mother Earth News Magazine in 2007. The article that describes the complete building process in detail was published August/September 2009. It is now free on the Internet: Low-Cost Multipurpose Minibuilding Made With Earthbags , by Owen Geiger.
This earthbag dome Instructable simplifies the process and illustrates each step of construction with photos. The two critical drawings are also included here. Please refer to the complete article before asking questions.
This multi-purpose dome can serve as a storage shed or cool pantry above ground, or as a rootcellar or storm shelter below ground. No building permit is typically needed, because it is below the minimum size required by building codes, is not inhabited and is not attached to a residence.
Earthbag structures provide a cool space in summer and an escape from the cold in winter (ideal for humans and animals), which means this earthbag dome is well suited for many purposes, like a quiet space for relaxing or playing music, as well as those listed previously. Depending on your needs, the most practical combination of uses might be a rootcellar/cool pantry for daily use and a disaster shelter for emergencies such as tornadoes or hurricanes.
The key concept that makes earthbag domes work is corbelling. This means each course (each row) of bags is inset slightly from the course below. Corbelled domes made of adobe and stone have been built for thousands of years. The concept has been applied to earthbags in the last few decades.
Basic project information:
18’ exterior diameter; 8’ interior diameter; 11’ exterior diameter, 50 sq. ft. interior floor space; total cost of materials: $300, which is about $6/square foot.
Tamper(s), round nose shovel(s), grape hoe or grub hoe (digging tool), 13” x 16” sheetmetal slider, knife, hammer, 2’ level, 2” x 4” x 10’ leveling board, tape measure, fencing pliers, handsaw, trowel, garden hose with spray nozzle, 6’ or 8’ stepladder
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, put about 12” of gravel in the trench, and added two stakes with string lines: a center stake with string line to measure the radius, and a stake in front of the door to measure the dome curvature. Bags or tubes can be used. We demonstrate bags, because they’re often available recycled for very low cost. My YouTube Channel has a short video showing how the dome was built.
Step 1: Dome Plans
Let’s briefly take a look at the plans so you’ll better understand the building process. The first drawing is the floorplan that shows the dimensions for the dome base and the angled buttresses in front. The buttresses provide reinforcing on both sides of the door and also act as retaining walls to hold back the earth. Make a rubble trench under the buttresses the same as the dome, and interlock (overlap) each course where the dome and buttresses intersect.
The second drawing is the dome section that shows key vertical dimensions, earthbag foundation, door and arch. Note the wood stake in front of the door. The string line on this stake guides the curvature of the dome (112” radius in this case). This dimension remains constant. Put the stake off to one side of the doorway so you’re not tripping on it during construction.