Traditional Farm Buildings
And I worry when I get weeds in my gutter....
We saw a lot of buildings in Norway with these sod or turf roofs, not all of them old buildings by any means. 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 large parts of Scandinavia. Sod is a reasonably efficient insulator in a cold climate. The birch bark underneath ensures that the roof will be waterproof.
The active, water-tight element of the roof is birch bark. The main purpose of the sod is to hold the birch bark in place. Roofs in Scandinavia have probably been covered with birch bark and sod since prehistory. During the Viking and Middle Ages most houses had sod roofs. In rural areas sod roofs were almost universal until the beginning of the 18th century. A new market has opened by the demand for mountain lodges and holiday homes and sod roofs have begun to reappear as an alternative to modern materials.
Birch bark is very suitable as a roof covering because it is strong, water-resistant and soil-resistant enough to last for generations, although 30 years was considered the normal lifespan of a sod roof in most places. Birch is common everywhere in Northern Europe, and its outer bark is easily stripped from the trunk in spring or early summer, while the sap is running. Removing the outer bark will not harm the tree, although the scar will remain for many years. A new, coarser bark will replace the stripped bark.
The sheets of bark must be stored flat under pressure to prevent curling. Left alone, a sheet will curl up into a tight roll, in the opposite direction of the natural curve of the trunk.
The bark is laid inside up directly onto the roof boards without any nails or other means of fastening. On roughly hewn or sawn roof boards, the friction alone will hold the layers of birch bark in place. They have to be weighted down with a heavier material to prevent them from curling or blowing away. Planks of split logs have been used, but sod has an additional advantage because it is an insulator.
Bark sheets were laid from the eaves upward, overlapping like shingles, and straddling the ridge. 6 layers of birch bark were considered adequate, but up to 16 layers have been recorded in roofs of high quality.
Sod or turf for roofing was cut from good pasture land, preferably with sandy soil. Pieces of sod must be laid out immediately after the birch bark, to keep it in place. The first layer of sod was traditionally placed with the grass down, as the wilted grass would protect the bark from acid humus and act as a drain. The grass of the second layer faced upwards to establish a solid surface. Grass roots would eventually permeate the bottom layer to create one solid structure. The finished roof would in time look just like a flower-studded meadow.
A total thickness of about 15 cm is enough to make the sod survive a dry summer. Most of Scandinavia has enough precipitation to let an established root system survive an occasional dry spell.
Traditional Farm Buildings
And I worry when I get weeds in my gutter....
We saw a lot of buildings in Norway with these sod or turf roofs, not all of them old buildings by any means. 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 large parts of Scandinavia. Sod is a reasonably efficient insulator in a cold climate. The birch bark underneath ensures that the roof will be waterproof.
The active, water-tight element of the roof is birch bark. The main purpose of the sod is to hold the birch bark in place. Roofs in Scandinavia have probably been covered with birch bark and sod since prehistory. During the Viking and Middle Ages most houses had sod roofs. In rural areas sod roofs were almost universal until the beginning of the 18th century. A new market has opened by the demand for mountain lodges and holiday homes and sod roofs have begun to reappear as an alternative to modern materials.
Birch bark is very suitable as a roof covering because it is strong, water-resistant and soil-resistant enough to last for generations, although 30 years was considered the normal lifespan of a sod roof in most places. Birch is common everywhere in Northern Europe, and its outer bark is easily stripped from the trunk in spring or early summer, while the sap is running. Removing the outer bark will not harm the tree, although the scar will remain for many years. A new, coarser bark will replace the stripped bark.
The sheets of bark must be stored flat under pressure to prevent curling. Left alone, a sheet will curl up into a tight roll, in the opposite direction of the natural curve of the trunk.
The bark is laid inside up directly onto the roof boards without any nails or other means of fastening. On roughly hewn or sawn roof boards, the friction alone will hold the layers of birch bark in place. They have to be weighted down with a heavier material to prevent them from curling or blowing away. Planks of split logs have been used, but sod has an additional advantage because it is an insulator.
Bark sheets were laid from the eaves upward, overlapping like shingles, and straddling the ridge. 6 layers of birch bark were considered adequate, but up to 16 layers have been recorded in roofs of high quality.
Sod or turf for roofing was cut from good pasture land, preferably with sandy soil. Pieces of sod must be laid out immediately after the birch bark, to keep it in place. The first layer of sod was traditionally placed with the grass down, as the wilted grass would protect the bark from acid humus and act as a drain. The grass of the second layer faced upwards to establish a solid surface. Grass roots would eventually permeate the bottom layer to create one solid structure. The finished roof would in time look just like a flower-studded meadow.
A total thickness of about 15 cm is enough to make the sod survive a dry summer. Most of Scandinavia has enough precipitation to let an established root system survive an occasional dry spell.