OOne of the key challenges in determining the role of windows in a green building is to create a design that will optimize energy efficiency by maximizing winter solar gains, and minimizing winter heat loss summer solar gains. This translates into the increased insulation value of windows in all orientations.  To help minimize summer heat gains, windows facing east and west should be reduced in size and area.  To improve daylighting, light shelves can be incorporated into the fenestration design, particularly on the south facades of the building.

Despite having less than one tenth of the insulation capabilities of walls, windows take up a majority of the wall area in traditional high-rise buildings, resulting in large energy losses.  A green design solution is the use of high-performance windows.  High performance windows include those with low-emissivity glazing, inert gas fills between panes, multiple glazing, and advanced framing materials and section design to minimize air leakage.  Aside from improved thermal insulation, high performance windows also reduce condensation, which obscures outdoor views, causes growth of mold, and damages material finishes.