Abstract: The roof ventilator includes a membrane of closed cell plastic so that it is rendered impervious to moisture and a pair of laterally-spaced open cell plastic strips adhesively secured to one side of the membrane, the strips being of foamed polyurethane. Specifically, the strips have a multiplicity of intercommunicating cells or pores so that when installed air can readily flow outwardly through the interconnected cells of the strips, yet inward migration of moisture is inhibited by reason of the many interlinked filaments or strands that form the various cells. The roof ventilator can be attched to a conventional roof by means of nails or an adhesive.