Buitenbogen

Buitenbogen is a term in Dutch architecture that refers to the outer curve of an arch—the exterior arc visible on the outside of a wall or structural element. This outer arc forms the external boundary of the arch, while the inner arc is known as the binnenboog or intrados. The wall thickness between the buitenbogen and de binnenboog defines the arch's depth and influences the arrangement of voussoirs.

In practice, the buitenbogen corresponds to the exterior surface of the arch, sometimes described in terms of the arch’s extrados; the inner arc along the arch’s underside corresponds to the intrados. In historical masonry, both curves may be seen in one opening, with the outer contour shaping the building’s silhouette and the inner curve carrying the load.

Construction and design: The radius of the buitenbogen, along with the arch type (semicircular, segmental, or multi-centered), affects appearance and structural behavior. When the outside radius differs from the inside radius, the wall thickness and the voussoirs are arranged to accommodate thrust and ensure stability.

Usage: Buitenbogen are found in arches in façades, arcades, bridges and gateways. They are discussed in architectural surveys to describe exterior contours, shadow play, and how the arch interacts with the surrounding masonry and openings.

See also: intrados, extrados, voussoir, arch.