Abstract: An improved vent for equalizing the pressure on the roof of a building includes a tube provided with a one-way acting valve therein for allowing air to pass from within the building to the open atmosphere but preventing entry of moisture air into the interior of the building. The valve includes a flexible flapper valve member mounted over an opening in a metal plate secured in face-to-face contact with an annular flange on one end of the tube. Condensation of moisture within the tube is prevented by a thin layer of insulation which lines the tube and which, in one embodiment of the invention, includes an integral annular flange sandwiched between the tube and the valve plate to prevent moisture condensation on the plate. An annular depression in the valve plate surrounding the valve opening diverts condensed moisture from the flapper valve to prevent valve seizure due to frozen moisture.