Sod
Sod or turf for roofing was cut from good pasture land, preferably with sandy soil. A naturally grown grass with a deep root system was desirable. The turf was cut into portable pieces, each about one foot (30 cm) square and about 3 inches (7.5 cm) thick, half the thickness of the finished covering. It was hoisted or carried up on the roof, or on a scaffolding.
Pieces of sod must be laid out immediately after the birch bark, to keep it in place. For this reason, the process must be carefully coordinated. Two workers will usually cooperate on the same strip of the roof, wide enough to be comfortably within reach. One will lay out the bark, the other will put sod on top.
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. More than 20 cm is superfluous, and the weight would be excessive. If the sod is too shallow, a severe drought will kill the vegetation, causing erosion and soil creep. Most of Scandinavia has enough precipitation to let an established root system survive an occasional dry spell. In very dry areas, it was customary to cultivate certain drought resistant plants - notably Sedum rosaeum, Allium fistolosum and sempervivum tectorum.
Read more about this topic: Sod Roof
Famous quotes containing the word sod:
“The symbol of perpetual youth, the grass-blade, like a long green ribbon, streams from the sod into the summer, checked indeed by the frost, but anon pushing on again, lifting its spear of last year’s hay with the fresh life below. It grows as steadily as the rill oozes out of the ground.... So our human life but dies down to its root, and still puts forth its green blade to eternity.”
—Henry David Thoreau (1817–1862)
“There grew pied wind-flowers and violets,
Daisies, those pearl’d Arcturi of the earth,
The constellated flower that never sets;
Faint oxlips; tender bluebells at whose birth
The sod scarce heaved; and that tall flower that wets
Its mother’s face with heaven-collected tears,
When the low wind, its playmate’s voice, it hears.”
—Percy Bysshe Shelley (1792–1822)
“‘Lay me a green sod under my head,
And another at my feet;
And lay my bent bow at my side,
Which was my music sweet;
And make my grave of gravel and green,
Which is most right and meet.”
—Unknown. Robin Hood’s Death (l. 65–70)