BODY FRAME STRUCTURE
The foundation stones are natural rocks on which rest square-shaped
posts, the bottoms of which are cut to conform to the contours
of the stone. The posts are spaced on 1 ken intervals (1 ken = around 1.8 meters) or at 1.5 ken intervals, connected at the top to the girders and beams and
joined together in the horizontal direction with many nuki (reinforcement braces) which penetrate the posts at various heights
to stiffen and strengthen the body structure. The beam span of
the body structure is usually 5 to 7 meters, but often reaches
10 meters in the case of large houses. In many cases, the interior
space can be expanded in the beam-axis direction by adding shed-roofed
projections on one or both sides of the building. In this case,
by using curved beams known as chona-bari between the main longitudinal beam and the outside row of posts,
it is possible to eliminate the intermediate row of posts to provide
a wider internal space (Fig.3).
The chona-bari beams come from trees which grow on steep mountain slopes, where
the tree trunk is forced naturally into a curved shape as it emerges
from its tilted root-base in the sloping soil and then bends upward
to grow vertically. With this curved shape the beam has increased
strength, serving as a natural arch. This is an example of the
superior usage of wood, both from the standpoint of efficient
utilization of domestic material as well as rational application
in a sophisticated structural system.
The usage of this type of beam, which provides the extra structural
strength required to support heavy snow loads, is one of the basic
structural characteristics of Gassho-style houses. It is not,
however, limited exclusively to the Shirakawa-go / Gokayama area;
similar curved beams can be found in other heavy-snowfall areas
in different parts of Japan.
A comparison of Gassho-style structural features with those of
typical farmhouses points out other unusual characteristics: the
post and beam members are larger and stronger than usual, and
the posts stand at regular I ken intervals (without the commonly-used "skip-span" framing method
used to make larger wall openings), and there is a greater-than-normal
quantity of horizontal penetrating braces to increase the rigidity
of the structure. These structural measures were necessary to
bear the unusually heavy snow loads on the large roofs.
