The etymological origin of the word 'window' lies in the Old Norse term, "windr Auga", implying eye of the wind. Similarly, its Sanskrit equivalent vatayan means passage of air. These clearly ascribe the primary function of ventilation that windows are meant for.
A window has three functions to perform. Light, view and ventilation. As part of the envelope system, window is a critical element of interface between indoors and outdoors. While rooms are sheltered spaces, windows make these habitable. They also modulate facades and lend a visual character and identity to the room.
As much the wall retards the external environmental vagaries, the window admits the same within. Therefore, its proportion is highly critical in the overall environmental management and effective climatic comfort. Research has proved that for hot and dry climate like ours, it is advisable to have 23% window area in a room.
Fenestration to facade ratio should not exceed 1:4. Against this wisdom, today's buildings often offer more than half and in curtain glazing all the way up to 100% of the window area. This naturally means heat ingress through solar radiation, excessive glare and uncomfortable light contrast. In addition, as a fixed glazing it absolves itself of any role in cross ventilation or breeze ingress.
Devoid of any manual operational controls, they remain fixed and thereby rigid to prevent any manipulation or permutation choices of its shutter openings. Thus, a pleasant outdoor environment can't be naturally invited inside by simply opening the window shutters. It requires dependence on mechanised services and energy-intensive devices to match and produce the same level of comfort as outside. An utterly nonsensical proposition.
Contrary to traditional dwellings, the window was tripartite with multiple shutters and manipulation flexibility. A typical window is vertically divided into three zones. The top one is a horizontal flap shutter that acts as a ventilator. The middle ones are side-hung dual leaf opaque shutters, while the lower ones are a dwarfed version of side-hung double leaf opaque shutters.
The top one works like a ventilator to allow movement of air and cross-ventilation for hot air to escape out, following convective principles of air circulation. It allows for two zone shutters to close for privacy during afternoons and evenings without affecting visual privacy. It also brings in diffused illumination without glare or haze.
Middle zone is primarily for viewing and communication. These shutters are voluntarily opened when one wishes to partake with the outside world. The lower most window is for wind. As cool air is heavier, it is best encountered at lower zones. Lower shutters allow for cool air to come through. It is also used to be most effective to cover floor zone as most activities are carried out squatting on the floor.
Thus, a window with a relatively smaller proportion can carry out fundamental roles of providing light, view and ventilation. It also allows for personal control and manipulation. Each owner can choose to permute and combine the zones and shutters based on time of the day, day in the year, seasonal variation, activity within as well as personal notions of privacy as well as security.
This is the reason why traditional dwellings such as Ahmedabad pols and their typology has successfully worked for six centuries.
Versatility, virility and validity render these windows sustainable, whether environment-wise or socio-culturally.