An insulation system of a building having a plurality of spaced-apart support members has an insulator with a plurality of ribs are formed thereon. A concave portion of each rib receives one of the support members. A panel covers, and is secured to the support members. An exterior covering element is secured to an exterior side of the panel. A radiant heat barrier is bonded between the insulator and the panel. The insulator defines air ventilation channels between the foam insulator and the panel for venting air from building. An insulator assembly for a building has a sheet of foam insulation with a plurality of channels intermittently formed in the sheet of insulation. Each channel has a concave side and a convex side. The concave side is adapted to receive a support member of the building. A radiant heat barrier is bonded to a surface of the foam insulation.