Tim and Robin O’Hara of Rancho Mastatal, an environmental learning and sustainable living center, used Robin’s design to build their home out of cob, wattle and daub, lime plasters, bamboo, locally milled wood, and recycled fence posts. A cob house is made from subsoil, water, and fibrous organic material such as straw. Sourced from local materials, cob houses are sustainable in terms of resource use and energy efficiency. Because the cob walls act as a thermal mass, the house is kept warm by passive solar heating, as the walls absorb sunlight during the day. The house is also kept cool during hotter temperatures. With earthen floors, an outdoor shower, a composting toilet, renewable energy systems, and locally grown food, this sustainable home and environmental learning center has stunning views of La Cangreja National Park.