Abstract: A slide ventilation assembly for a roof window installation has a multiplicity of elongated walls defining an enclosed space with two of the walls extending at 90.degree. to one another, and a connector wall piece disposed between the adjacent ends of the two walls. The two walls have apertures spaced along the length thereof, and elongated ventilation slides are slidably mounted on them. The slides have apertures spaced along the length thereof and are slidable between a first position in which their apertures are aligned with the apertures in the walls. A connector connects the slides for concurrent movement thereof, and a manipulatable operator is provided to move the slides to effect alignment of the apertures in the slides with the apertures in the walls to allow air to pass through the walls and enclosed space.