binnenboog

Binnenboog is a Dutch architectural term that refers to the inner curve of an arch—the concave side that faces the interior space. In more technical language this inner surface is called the intrados; the outer, convex curve is the extrados, or buitenboog. The binnenboog and buitenboog together determine the arch's overall profile, though in practice binnenboog is often used interchangeably with intrados in descriptive writing.

Binnenbogen appear in many arch types, including the semicircular Romanesque arch, the pointed Gothic arch, and more complex ogee or elliptical forms. The inner curve may be plain or elaborately molded with mouldings, coffers, or decorative cartridges. In masonry the intrados is formed by the inner faces of the voussoirs and the springing line, and it is in compression.

In Dutch architectural usage the term binnenboog is primarily descriptive and found in historical texts, restoration reports, and general descriptions of openings. For technical drawings and precise specification, intrados is the preferred term, whereas binnenboog is more common in non-technical descriptions or discussions of historic architecture.

Related concepts include intrados, extrados, arch, voussoir, and Gothic architecture.