Abstract: A system for use with a conventional building such as a mobile home having an existing roof includes a sheet having dimensions generally conforming to the roof with a central opening therein. A plurality of brace plates extend from the peripheral edge of the roof-sheet combination to the center opening, to hold the sheet in spaced relationship above the roof so as to define a void therebetween communicating with the central opening, and further defining peripheral openings permitting movement of a cooling fluid from the ambient into the void. Sliding and overlapping members are provided for closing the central and peripheral openings in order to define an insulating layer above the roof.