Abstract: An insulating system for reducing heat loss from a structure during one part of the day and for permitting light to enter the structure during another part of the day, this system comprising a roll mounted on the structure, a flexible sheet of material wound around the roll, structure supporting the roll immediate its length and engaging portions of the wound sheet, and means for unwinding the sheet from around the roll and deploying it in a plane and for rotating the roll to rewind the sheet therearound; and a system for detecting build-up of snow or ice.