Norwegian Grass Roofs
The norwegian translation is “torvtak”, which means “turf roof”. These roofs are covered with sod on top of several layers of birch bark on gently sloping wooden roof boards.
Keeps walls straight: 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. Therefore keeping straighter wooden walls which were prone to warp with changes in moisture in the wood. In winter, the total load may well increase to 400 or 500 kg per m² because of snow.
Good form of insulation: Sod is also a reasonably efficient insulator in a cold climate. The birch bark underneath ensures that the roof will be waterproof.
Inexpensive materials: A sod roof is well suited to a barter economy because the materials are abundant and inexpensive, although the work is labour intensive. But in the old days, a household would usually have a lot of manpower available and neighbours would usually be invited to take part in the roofing party, similar to a barn raising in the US.
These days the grass roofs are built out of tradition, and simply because they look nice and fit in with the Norwegian countryside.
Traditional black Norwegian wooden houses
In the past, makers of Norwegian log cabins would place moss in between the logs that made up the walls. Moss was useful because it did not rot, and it reduced wind draughts occurring between the logs making up the walls of the cabin. The wooden logs were also dipped in tar. This would harden the wood, therefore remain straighter for longer. It also prevented the wood from being attacked by parasites. Nowadays this is against environmental regulations, therefore the wood pannels are no longer soaked in tar like they used to.