Alternative construction options such as earthbags are gaining popularity because they are sustainable, eco-friendly, and energy-efficient.
Building an earthbag home underground is an excellent way to enhance its energy efficiency and insulation properties.
However, before you take the leap, the question remains, “Can you build an earthbag home underground?”
Although you can build an earthbag home underground, you must be careful with its design and engineering to withstand the earth’s hydrostatic pressure. A rule of thumb is to have curved walls, sufficient insulation, and a dome-shaped roof for your underground earthbag home.
In the rest of this article, I’ll discuss four examples of underground earthbag homes. Let’s get started!
1. Low-Cost Multipurpose Minibuilding (Earthbag Building)
This is an excellent example of an underground house with earthbag walls and an earthbag dome forming the roof, designed by Owen Geiger.
The structure has an underground diameter of 8 feet. It also protrudes 8 feet above the ground.
The design takes on a dome-shaped roof to enhance its strength. Since underground buildings are at a higher risk of earthquakes, the earthbag dome provides more stability to withstand pressure.
The following are the essential features of this underground earthbag home design:
- A slope: Building underground provides the benefit of earth sheltering, reducing HVAC costs, but exposes the house to stormwater. Therefore, the design incorporates a slope on the front side to drain the water. This is a crucial consideration because, although earthbag walls are not severely affected by water, they risk mold growth if water accumulates in the bags.
- Filling the bags: Earth bags must be properly filled to eliminate air spaces that can weaken the wall. Filling involves using buckets to scoop soil or gravel into the bags. Most bags are filled with approximately four buckets of road base. However, it depends on the size of your earth bags.
- Tamping: Tamping is important for earth bag construction because it enhances the house’s structural strength and makes the bags even. It also compacts the soil to prevent the walls from collapsing due to external pressure. You can use an agile 45-inch hand tamper or any larger option. Once tamped, you can rest assured that all bags are adequately packed with the fill material. Adding barbed wire between each course of bags helps hold them together, too.
- Arch form for the door: You can place old tires around the earthbags to create a structurally sound arch shape for the door. Old tires work well as you can easily shape them into any desired form.
According to Greiger, this is a cheaper design that will cost you approximately $300 if you go the DIY route.
2. Spiral Earthbag House
The plan features an exposed timber ceiling, 740 square feet (68.75 square meters) interior, one bathroom, a living room, and one bedroom. This is an ideal house plan for a family of four.
The features of this earth-sheltered house plan include:
- A trench foundation with perlite or scoria for insulation
- Gravel or soil-filled earthbags to create walls, with barbed wire between each layer for added structural integrity.
- Earth or stone for floors
- Clay or lime plaster for finishing the inner walls
- Roofing options like green roofs, domes, or metal roofs to collect rainwater
- Sufficient insulation materials like cellulose, cotton, or rice hulls for the roof
- Energy-efficient doors, windows, and house appliances
According to Greiger, the following are crucial considerations for building a spiral earth-sheltered earthbag home with this design:
- Floors: Tamped earth floors made of stone, recycled brick, or earth. The tamping process involves screening off the large aggregates from the base using screening material and wetting it before tamping. After tamping, wait for the floor to dry before sealing it with boiled linseed oil.
- Wall finishing: Apply clay or lime plaster since they are more permeable to moisture and vapor. This prevents the accumulation of moisture within the earthen walls.
- Windows and doors: The readily available standard-sized doors and windows are ideal. However, you must be careful with older windows because most are not energy-efficient.
3. Root Cellar With Earthbag Walls
This is a family’s off-grid underground earthbag building for food storage. This was an excellent option for this couple because earthbag construction is dirt cheap, durable, and sustainable.
The primary material for this project was 14 by 26-inch polyethylene sandbags filled with the surrounding dirt available on-site before being tamped down. The tamping was done to ensure sufficient soil compaction to make the subterranean structure durable. Barbed wire between each course of bags would also add structural strength.
The major challenge encountered during the construction of this underground earthbag cellar is the high water table in that part of Alaska. As I mentioned, water should be your number one focus when building an earth-sheltered earthbag house.
To counter the water challenge, the couple decided to raise the floor from 9 feet (2.74 meters) to 7 feet (2.13 meters) using the surrounding dirt and mixing it with gravel.
Finally, they wrapped the exterior side of the earthbags using a house wrap to control moisture ingress.
Watch the videos above for the entire building process.
4. Epic Underground Bunker Earthbag Room
This is a family’s underground earthbag bedroom built in an arid area. The family’s focus was to live sustainably by relying on solar, rainwater, and eco-friendly building materials.
As the condition dictates, arid areas don’t have sufficient resources for construction. Therefore, earthbag construction came in handy for this couple besides living sustainably due to the lack of other materials.
The construction process for this underground shelter started by excavating the ground to create space for the earthbags. The excavated earth was also used to fill the earthbags.
After the excavation, a trench was created to hold the earthbags before filling and leveling the center with gravel.
Each layer of earthbags was tamped and packed closely, with barbed wire between each course of bags to provide structural integrity to the walls before moving to the next layer. In addition, the exterior side of the underground wall was covered with a tarp to prevent ground moisture from infiltrating into the earthbags, as this is a recipe for mold growth.
Finally, the roof was made from wooden frames covered with oiled cinder blocks for protection against the elements.
Click on the screenshot above to watch the video demonstrating the entire building process.
So, Can You Build an Earthbag Home Underground? – Final Thoughts
Building an underground home enhances thermal insulation capacity because the earth offers excellent thermal mass. However, moisture and water penetration are the main challenges when constructing an earthbag building underground.
The best way around moisture and water penetration is wrapping a tarp or house wrap around the outside of the exterior walls. Doing so results in an energy-efficient house that is resistant to the elements.
We understand how challenging it can be to find a reliable earthbag house builder. So, to make your work easier, we compiled a list of 3 earthbag home builders in the USA.