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How can underground buildings maintain more stable indoor temperatures?

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Underground and earth-sheltered buildings maintain stable indoor temperatures by utilizing the earth itself as a natural, dependable source of climate control.1

At depths starting approximately 1.5 meters (5 feet) below the surface, the ground maintains a relatively constant temperature—often cited as roughly 11 °C (52 °F)—which remains largely unaffected by the fluctuations of outside air temperatures. By surrounding a structure with earth, architects can leverage this thermal mass to moderate the interior environment, significantly reducing the energy required for heating and cooling.213

In addition to the passive benefits of earth-sheltering, some buildings incorporate geothermal heat pumps to further enhance this stability. These systems circulate a fluid through underground pipes to exchange heat with the soil or groundwater. During colder months, the system draws heat from the ground to warm the building, while in warmer months, it transfers heat from the building back into the ground, effectively using the earth as a thermal reservoir to maintain a comfortable indoor climate.2