One of the primary building blocks of an Earthship is recycled automobile tires. When filled with compacted earth, it forms an earth brick, a solid piece of earth encased in a steel belted rubber. These earth bricks are the major building pieces to the overall structure of the building. The walls created with earth bricks are virtually unbreakable.

Offgassing is not a problem, because although tires give off noxious gas when new, they lose their toxicity by ten thousand miles, and in an Earthship they are encased in plastic and adobe.