A facade/wall system comprises a number of modules. Each module comprises a plurality of insulating panels which have connection means on opposite sides thereof for interengaging the panels together at joints between the panels. Reinforcing elements in the form of top hat sections bridge the joints between adjacent panels. The top hat reinforcement elements used to interconnect adjacent panels in a module ensure that the composite panels act together as monolithic structure that creates a diaphragm while providing a surface to which cladding can be fixed and also providing a cavity between the panels and the cladding attached to the modules. They stiffen the panels and thereby enhance resistance to deflection. The system is cost effective and relatively easy and quick to install.