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. Until the late 19th century, it was the most common roof on rural log houses in Norway and large parts of the rest of Scandinavia. Its distribution roughly corresponds to the distribution of the log building technique in the vernacular architecture of Finland and the Scandinavian peninsula. The load of approximately 250 kg per m² of a sod roof is an advantage because it helps to compress the logs and make the walls more draught-proof. In winter the total load may well increase to 400 or 500 kg per m² because of snow. Sod is also a reasonably efficient insulator in a cold climate. The birch bark underneath ensures that the roo