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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. Its distribution roughly corresponds to the distribution of the log building technique in the vernacular architecture of Finland and the Scandinavian peninsula. 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. In winter the total load may well increase to 400 or 500 kg per m² because of snow.〔Drange 1992:96〕 Sod is also a reasonably efficient insulator in a cold climate. The birch bark underneath ensures that the roof will be waterproof. The term ‘sod roof’ is somewhat misleading, as 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. The roof might just as well have been called a "birch bark roof", but its grassy outward appearance is the reason for its name in Scandinavian languages: Norwegian and Swedish ''torvtak'', Icelandic ''torfþak''. A sod roof is well suited to the dynamics of a barter economy because the materials are ubiquitous and cost nothing, although the work is labour-intensive. However, a typical household in the era that sod roofs were most common would usually possess a lot of manpower, and neighbours would typically be invited to take part in the roofing party, similar to a barn raising in the United States. The Norwegian term ''dugnad'' denotes an established custom in rural communities, where large undertakings were accomplished with help from neighbours.〔Hjelmeland 1993〕 ==History== 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.〔Berg 1989:71〕 Churches and other buildings with steeper roofs were covered with boards, wood shingles, or lead. In rural areas sod roofs were almost universal until the beginning of the 18th century. Tile roofs, which appeared much earlier in towns and on rural manors, gradually superseded sod roofs except in remote inland areas during the 19th century. Corrugated iron and other industrial materials also became a threat to ancient traditions. But just before extinction, the national romantics proclaimed a revival of vernacular traditions, including sod roofs. A new market was opened by the demand for mountain lodges and holiday homes. At the same time, open-air museums and the preservation movement created a reservation for ancient building traditions. From these reservations, sod roofs have begun to reappear as an alternative to modern materials. The more recent idea of the green roof is developed independently from the traditional sod roof, but could benefit from the experience gathered during hundreds of years in Scandinavia. people thought it look cool so they put it on the Sod houses. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「sod roof」の詳細全文を読む スポンサード リンク
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