iron

An iron frame is composed of unalloyed iron members, usually beams, plates, and connecting elements. Structural iron frameworks are used sometimes in small and very old buildings, often pre-dating advances in steel construction.

The iron members make up the supporting skeleton. Iron used only for decorative panels or an exterior covering does not establish the material of the load-bearing frame.

The unalloyed material specified here distinguishes this frame from a steel frame. The shape of a beam or the age of a building alone does not establish that material distinction.