抄録
Among the extant single-story dapo type buildings (having a densely arranged bracketing unit layer), seven buildings have double layers of interior bracketing units: an upper-layer and a lower-layer. The aim of this study is to find out their character, historical development and significance. Firstly, they are classified into Group A and B by the role of upper-layers as structural supports. Each group is then further divided into two subgroups, according to the existence of projections in their upper-layer bracketing units. Groups A1 and B1, the no-projection types, are used in the same building from late Goryeo as a multi-layered system; that could be a part of the general method of dapo type buildings in late Goryeo and before. The upper-layers belonging to Groups A2 and B2 have projections of their bracketing units; these are mainly to achieve a more splendid interior aspect, by imitating the valued aspects of other bracketing units in this period; the structural roles of those projections are however relatively trivial. The construction of upper-layers in roof structures had commenced by the 11th century. In extant Korean buildings, the 17th century saw the peak of the development of double-layered systems, before their decline in the 18th century.
