A ventilating damper assembly particularly adapted for use in conjunction with an evaporative cooler system for architectural structures includes a duct inserted into the ceilings of rooms cooled by the evaporative cooling system to discharge air from within the room through an attic space located above the ceiling and out into the atmosphere through vents in the attic. The ventilating damper assembly has a gravity-closed pivotally-mounted lid on the upper end of the duct to keep the duct closed whenever the evaporative cooling system is not in operation or whenever backdrafts from the attic occur. Positive air pressure within the room moves upwardly through the damper assembly, opening the lid to permit air to escape from the room into the attic, thereby maintaining the air flow necessary for efficient operation of an evaporative cooler and additionally exhausting the relatively cool air into the attic space above the ceiling to further improve the cooling efficiency of the system. Temperature sensitive normally-open self-closing anti-draft dampers close the duct whenever abnormally high temperatures occur.