Extensive Definition
Arris is an architectural term that
describes the sharp edge formed by the intersection of two
surfaces, such as the corner of a masonry
unit; the junction between two planes of plaster or any
intersection of divergent architectural details. Also the raised
edges which separate the flutings in a Doric column.
The origin is from the Latin 'arista' meaning the
beard of an ear of grain or the bone of a fish. See also arête.
An arris rail is a structural element, whose
cross sectional area has two sides forming a right
angled triangle. Arris rails are usually made of wood, and are manufactured by
cutting a 45° chamfer
from both edges of a timber, at the end of the boards. They are
used for structures which require joining two timbers at right
angles; for example, connecting a wood post and beam. Another
common use is for the horizontal rails of timber fences, since the diagonal edges
prevent water from collecting on top of the wood and thus rotting
the timber. It also adds an element of security, since the fence is
harder to climb.