Abstract: A building roof deck structure having significant fire resistance comprises a plurality of wood cement or fiber cement panels lying in a common plane and having abutting edges with aligned grooves extending along the abutting edges inwardly of the panels. Structural steel, T-shaped members are positioned between the butting edges with the flanges of the T-shaped members extending into and closely enclosed by the aligned grooves. The webs of the T-shaped members are positioned to extend in a direction outwardly of the building. A fire resistant grout is placed between the abutting edges to totally enclose the webs of the T-shaped members; and, urethane foam insulating panels overlie the wood cement panels and a waterproof roofing layer extends over said urethane foam panels.