Having almost no insulation value, earth walls instead provide thermal mass, slowing heat transfer from exterior to interior spaces during the day and from interior to exterior spaces at night. The rate of heat transfer through a rammed earth wall is about one inch (2.5 cm) per hour. In the desert, this thickness prevents the sun’s heat from reaching the building’s interior before nightfall. Substantial drops in air temperature at night cause the walls to cool off again before sunrise. This slowing down of heat exchange is known as the “thermal flywheel effect” and it is one of the primary benefits of living in an earth house.

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