Structural zoning is the recognition of forms in spatial designs. It can be used by a structural designer to develop a structural system. This paper will start with the presentation of a proof that neither user action nor a two-dimensional approach -two existing approaches of zoning- are able to recognize all possibilities for the application of a structural design to a spatial design. Only full three-dimensional structural zoning is considered to be an appropriate instrument to give useful solutions. Two new concepts will be presented to overcome problems for three-dimensional zoning: (1) Geometrically Related Reducers and (2) Matrix Coupling. These concepts are first defined in a general form and thereafter the definitions are condensed into a practically applicable format. Both concepts are demonstrated when finding rectangular zones in spatial designs up to 44 separate spatial entities. They are programmed procedurally using the C++ computer language and are used for a comparison between structural designers and computer performance.