Internal structural mullion for standing seam panel system

An internal structural mullion for a standing seam panel system, comprising:

• a hollow main extrusion having an extrusion interior, an open side, an opposing closed side, an innermost portion, and a main hooked portion opposite said innermost portion;
• a secondary extrusion having a first leg portion, a medial leg portion, an end leg portion, and a leg hooked portion, said secondary extrusion adapted to clamp onto said open side of said main extrusion with each said main hooked portion and said leg hooked portion configured to span said standing seam and engage a pair of panels;
• and,
• a means within said extrusion interior for receiving and containing one or more reinforcing steel bars to aid in supporting each of said mullions.

A standing scam panel system, comprising:

• at least a pair panels meeting at a joint, said panels have standing flanges and detents near bases of said flanges;
• a mullion including a main extrusion and a secondary extrusion, said main extrusion having an innermost portion, and a main hooked portion opposite said innermost portion, said secondary extrusion attached to said main extrusion and having a leg hooked portion opposite said main hooked portion to form a pair of hooked portions, said hooked portions engaging said detents of said panels;
• slotted holes defined within said main extrusion;
• screw fasteners passing through said slotted holes of said main extrusion and into a building substrate, wherein said innermost portion of said main extrusion is attached to a building substrate such that said mullion is adapted to move vertically along said building substrate to accommodate expansion or contraction of said panels.