Abstract: A ventilating appartus for installation in a ventilation opening in a building foundation includes a peripheral border having detachable lateral extension tabs for selective retention to be mounted in a mortar joint in brick-type construction and, alternatively, for selective detachment for disposition flush with laterally-adjacent foundation surfaces for edgewise disposition thereon of siding in siding-type building construction. No border is utilized in an alternative embodiment of the ventilating apparatus to facilitate mounting thereof to the outward face of a building foundation as a replacement for broken and deteriorated ventilating apparatus, a separable side portion facilitating such mounting in buildings of siding-type construction. A slotted shutter-like mechanism is provided for convenient opening and closing operation of the ventilating apparatus.