Roofs of sod have sheltered mainland Scandinavians through countless winters and summers. But those who migrated from Norway"s grass-roof log cabins to this Icelandic tundra in the 9th century found none of the rich timberland of their homeland—just wispy birch forests and grassy fields. To survive the cold, they took the old turf roof concept and built on it, encasing not only the roofs but the walls of their birch-framed homes in layers of living, insulating soil.