Answer:
The Sod houses were built as an alternative to the log cabins by the settlements of the Great Plains of Canada and the United States. Initially, it was used for Animal shelters and Fences. In the prairies where the building materials were not present Sods were built from the grass. The grass was also used for building houses but when the building materials were available they were used in construction. Hence it can be said that lack of trees and building materials was the reason for building sod Houses in Great plains.
