Abstract: The roof block is highly versatile in its applications, and includes recess-forming structure that segregates and cradles a multiplicity of transversely extending conduits and other elongate members; channel-forming and passage-defining structure that facilitates the assembly and stable support of threaded rods for the attachment of accessories; structure for securing, and facilitating affixation of, hold-down means for supported members; and elements that facilitate the unified, compact assembly of a multiplicity of like blocks. The roof block is of lightweight and strong construction, is convenient to use, and is practical and economical to manufacture in bulk.