Above: Farm house in Keldur, Iceland. These are “earth sheltered” houses, an ancient form of passive solar, sustainable architecture. It’s the practice of “packing earth against building walls for external thermal mass, to reduce heat loss and maintain steady indoor temperature.”
From Wikipedia: “A sod roof or turf roof is a traditional Scandinavian type of green roof covered with sod on top of several layers of birch bark on gently sloping wooden roof boards.