Abstract: An improved photovoltaic roofing system (10) includes a roofing membrane (12) overlying a top surface (14) of a roof deck (16), an insulation layer (18) above the roofing membrane (12) and a photovoltaic panel (20) above the insulation layer (18). The improved photovoltaic insulation layer (18) component defines a predetermined number of drainage channels (30) between the insulation layer (18) and the roofing membrane, and/or a predetermined insulation layer thickness, and the predetermined number of drainage channels (30) and/or thickness is a function of variable drainage requirements and/or variable insulation requirements of the roofing system (10). A photovoltaic IRMA roofing system (72) replaces traditional IRMA roofing system (73) ballast materials (79) with a combined weight of concrete topped (83) insulation layer and photovoltaic panels (80) to meet a predetermined minimum weight per unit area requirement of a specific roofing system (72).