The building is divided into two parts. The ground floor part is the bottom portion of an earthbag dome with a 18’ internal diameter. It is surmounted by a dome made of cob (earth + sand + straw) and eco-bricks (plastic bottles filled with trash) with a 13’ internal diameter. The domes follow the shape of an inverted catenary as three dimensional representations of the arch action.

The building is built along a rammed earth tire retaining wall as the North half of the ground floor level is surrounded by earth. However, the retaining wall is not part of the building as the earth lateral pressure would jeopardize the structure viability. Instead, the retaining wall wraps around the building leaving a gap between the tires and the dome structure which is backfilled with earth. A plastic membrane is added between the dome wall and backfilled earth in order to prevent water infiltration in the wall.

The earthbag dome is made of stacked courses of polypropylene bags filled with a mix of earth, sand and binder (cement for bottom courses and lime for top courses). Two lines of barbed wires are laid out between each course to maximize interlocking between bags. A concrete bond beam is poured on top of the earthbag wall to tie the whole structure together. In addition, columns made with reinforced concrete and recycled aluminum cans are added at both levels on the inside surface of the dome to reinforce the structure.

At both levels, a horizontal buttress made of the same material as the dome is added around the bottom of the dome wall. This creates a tension ring able to withstand the lateral outward forces stemming from the dome forces balance.

However, on the ground floor level the buttress is only present at the South half of the building as the lateral pressure imposed by the backfilled earth on the North half is sufficient enough to resist the dome outward forces. The South half buttress includes a sink made with mortar and a vertical concrete buttress located next to the entrance area. This vertical buttress compensates for the absence of a horizontal buttress in the door area and alleviates the impact of having a large door opening at the bottom of the building on the global structural stability.

The earthbag dome is founded on a course of car tires filled with gravel. This foundation provides a solid footing for the dome while preventing any water infiltration via capillary action. Similarly, the ground floor slab (made of layers of cob covered by a 2” thick concrete slab) is placed on top of a 8” thick layer of gravel in order to avoid any contact between the concrete and ground water.

The first floor slab is made of a 4” thick concrete slab with permanent bamboo formwork carried by concrete beams tied into the bond beam. The slab extends beyond the bond beam on the South half of the building to create the balcony slab. This balcony slab is carried by the extension of the first floor beams and bamboo members filled with reinforced concrete cantilevering from the bond beam.

All window and door openings in the dome follow the geometrically-stable arch shape to avoid the presence of lintels in the dome.

Around the North half of the building, a 180 sq ft patio space is created at the first floor by the addition of a timber roof carried by concrete beams resting on concrete posts and the dome itself. The patio floor is made of a single course of rammed earth tires laid on backfilled earth and covered with earth.

Ground floor exterior finishes are made of cob (earth + sand + straw). On the inside, a thin metal grillage (usually called “chicken wire”) is nailed to the bags and wrapped into a thin layer of mortar (cement + river sand) covered by a form coat (cement + lime + coarse sand) and a final coat (cement + lime + fine sharp sand).

First floor interior finishes are made of two layers of plaster: a form coat (cement + lime + coarse sand) and a final coat (cement + lime + fine sharp sand). The exterior finishes are similar with the addition on the outside of a limewash (lime + nopal cactus juice). Finally the outside walls are sprayed with a layer of water-repellent on the outside to protect the lime from rainwater.

Regarding rainwater drainage strategy, the first floor buttress slopes towards a PVC pipe feeding the ground floor sink. Thus, any rainwater falling along the dome ends up in this sink. Additionally, the balcony slab slopes towards its outer edge where drainage pipes evacuate rainwater.