US Patent 9523202 Roofing panel with interlocking clipping system

Metal roofing panels have a forward edge portion with a downwardly extending skirt and return flange and a rear edge or headlap portion with an upwardly open channel and a locking tab extending over a portion of the upwardly open channel. A method of installing the roofing panels includes nailing a lower course of panels in end-to-end overlapping relationship to a roof deck. The forward edge portions of panels in the next higher course of panels are then pressed downwardly into the upwardly open channels of the lower course panels. The return flanges of the upper course panels snap beneath the locking tabs of the upwardly open channels thus locking the panels together and forming a watertight connection between courses of panels.