A roof system and related methods for installing the roof system. The roof system includes a roof diaphragm including a nail board and an insulating panel connected to the nail board, wherein the insulating panel is adapted to be positioned between the nail board and a roof frame so that the insulating panel engages the roof frame. In several exemplary embodiments, the nail board comprises one or both of: oriented strand board (OSB) and plywood. In several exemplary embodiments, the insulating panel comprises one or both of: a closed-cell rigid polyisocyanurate (polyiso) foam core and a polystyrene foam core. In several exemplary embodiments, the roof system further includes a plurality of nail board fasteners connecting the roof diaphragm to the roof frame, the nail board fasteners each extending through the nail board, through the insulating panel, and into the roof frame to a depth.