Eco-friendly architecture and green buildings depend largely on elevation design, and specifically window design.
It is a paradox. Without consumption of sunlight we cannot live; equally well, without protection from sunlight we cannot live. In a modern context, this apparent contradiction needs to be resolved by the design of windows, hence eco-friendly architecture and green buildings depend largely upon the elevation design in general, also called as façade treatment, and specifically window design.
If we search for the essentials of architecture as shelter making, we end with up three parameters. Shelter from heavy rain, protection from cold wind and shade from harsh sunlight. The first is served by the roof; the second by the walls; and the last by both roof and walls. Of course it would be a dark box if only roof and walls exist. As such, to let the required air and light, windows were installed by the early human settlers. They were small, being built into the building volume, hence naturally protected. Contrastingly, today windows are large, placed at the open edge of the wall, exposed to vagaries of nature, demanding adequate measures not to let rain in and stop direct sun into the building.
Traditionally, most regions of India did not have the projection, nowadays called as concrete chajja. The sloping roof overhang was so deep, it would cover up the wall and window opening. Alternately, there would be a wooden bracket supporting the sloping sunshade over the windows. In case of flat roofs in hot arid regions, small stone slabs or sometimes an ornate window design as a box can be seen. The formal concrete slab projection as chajja appears to be a post-independence phenomena, further popularised by PWD norms. Irrespective of cardinal directions, sun movement patterns, degree of shading required, type of building or any such criteria, we have been adding this concrete slab over the window everywhere. Most often, we do not know how effective this shading device has been.
Incidentally, in dense urban housing areas, the chajja may also do more harm than benefit. With neighbouring building standing tall, the whole wall of a building can be shaded, ruling out the need of chajja shades. With narrow setbacks between two houses where no direct sunlight reaches the windows, the chajja would further reduce the incoming indirect light, making the houses darker. When a chajja faces the direct sun, the air around it heats up, which trends to enter the house, increasing the interior heat gain. There have been numerous cases where chajja becomes a point of water ingress.
All these above notes are not to negate the need for chajja; they are also needed for stopping rain, add elevation attraction or protect the wall from rain water flow along the surface.
The point is about designing studied and properly reasoned solutions for shading a building, without losing out on indoor light or air. Incidentally, all such climate responsive buildings have also to be attractive and culturally appropriate.