COMPOSITE STRUCTURAL BEAM

Described herein is a composite structural beam which comprises spaced apart upper and lower panel structures， each panel structure comprising an outer panel superposed on and partially overlapping an inner panel， a pair of spaced apart sidewalls and extending perpendicularly to the upper and lower panel structures， a central wall extending parallel in between the sidewalls and perpendicularly to the upper and lower panel structures， and two structural caps positioned at opposite longitudinal ends of the beam. The elements are assembled and tightly joined together to form a structural beam having a closed cuboid structure with two internal cavities which may include an isolating material. The beam further comprises lateral edges and optionally longitudinal edges that are configured to form lateral and longitudinal shiplap joints for joining together identical structural beams side-by-side and， optionally end to end， for rapidly building floors， walls and/or roofs.