A parapet-like component for a building which includes an air plenum. The plenum is a multipurpose structure which allows for transfer of a predetermined amount of heat from the outside into the building. The plenum includes translucent surfaces which allow light to enter the building and concurrently provide insulation against loss of heat from within the building towards the outside. The parapet-like component can be operated reversibly in allowing for cooling of the interior of the building when its temperature exceeds that of the outside.The structure is highly functional and also is aesthetically pleasing, having the general appearance of a mansard.The novel design of the invention allows for and incorporates the use of traditional and widely accepted building and architectural practices and esthetics.In a preferred embodiment, the plenum has an exterior wall of a tinted plastic or glass and a clear inside wall of plastic or glass.The structure is relatively easy to conform to conventional architectural plans.Considerable savings in both heating and lighting costs are achievable by the system without increase in building construction costs.