SOD ROOF KONSEP

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.^[7] 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,^[8] 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.^[9][10]




To stay in place the sod must be supported by strong beams along the eaves. These logs or beams (Norwegian: torvvol) come in a variety of shapes and sizes, depending on the quality and status of the building, and on local tradition. An equivalent English term would be turf log.
The most common turf log is an undressed fir log 5 to 6 inches across. Also fairly common are squared timbers of similar size. In some districts planks raised on edge were used.^[11] Other traditions called for a more elaborate cross section with the appearance of a fascia, approaching "real" architecture.

The turf log was fastened to the roof boards and underlying rafters with naturally grown wooden hooks, preferably from durable juniper. The hooks were fastened with wooden pegs and covered by additional sheets of birch bark. Turf logs are also known to have been held in place by rafters hewn from logs with one root branch left to form a bracket. This method made for extremely cumbersome maintenance. When the brackets disintegrated, one would have to tear up the whole roof to renew all the rafters. A more refined fastening device was the kolv, an elaborately shaped stick of wood, around 60 cm long, pegged to the roof and extended through a hole in the turf log. Its wider protruding head would hold the log in place.^[12]
Erosion at the verges was in some districts prevented by means of similar logs, sometimes joined crosswise at the gable top. More common was a row of rocks gathered from the fields.^[4] Verge boards were not a feature of ancient log buildings with sod roofs, but were introduced during the 17th and 18th centuries through influence from urban architecture with tile roofs.^[13]