Sod Roof - Birch Bark

Birch Bark

Birch bark is eminently 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 bark is easily stripped from the trunk in spring or early summer, while the sap is running. One incision with a knife lengthwise down the trunk between two branches will produce a correspondingly wide sheet, its length equal to the circumference. The outer, flaky (white) bark is pried loose from the inner (green or brown) layer, the phloem. Removing the phloem will cause the tree to die, but 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. But 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. The first layers project about 8 cm along the eaves, where they will curve down around the edge of the outer board to form a throating. Extra long sheets will straddle the roof ridge.