An apparatus for applying an improved adhesive to a series of sheets of insulation having drainage channels, wherein the apparatus includes a frame with a power-driven conveyor, a magazine for receiving sheets in stacked relation, and an elongated adhesive dispensing hopper adapted to apply an adhesive mixture having spacer beads or particles mixed therein on the top surface of each sheet of insulation adjacent to the drainage channels and including a shutter mechanism for forming transversely extending substantially adhesive-free pathways between the drainage channels and a screed attached to the hopper having optional scraper blades which wipe away any adhesive that may flow in the drainage channels.