Openings are essentially of THREE types: nominally used for egress, transit-able in an emergency and not serving any of these two functions yet functional or decorative.
Openings align with the floor on one or both sides, to facilitate floor level movement goods, people and animals. Though thresholds obstruct movement serve functional, structural and spiritual purposes.
Openings placed at higher sill level, such as the windows -away from the nominal floor level, are chiefly used for seeking illumination, view and ventilation. In hot humid climates lower sill levels allow body level air movement whereas in colder climates higher sills helped deflecting the cold breeze. In very tall buildings a high sills cuts off visual contact of the ground level terrain, presenting sky view only.
Windows have many grades, of ‘high to low’ sill levels, as referenced from interiors or exteriors. A high sill from interior space cuts off the view to the outside as in medieval cathedrals. A low sill or zero sill window ‘opens’ a space as in case of traditional Japanese houses. The upper floor windows of a glass curtain high rise building, clerestory windows and skylights offer a static view, lacking in dynamism.
Openings not meant for nominal or emergency egress are like upper level windows, rose or oculi windows, sky lights, lantern windows, transom and top-lite openings, delivery hoppers and wind catchers.
In openings meant for egress the degree of conveyance may have been intentionally made difficult or easier. A French window is a door for conveyance, and a trapdoor or a hatch door is a window for all purposes. A door could occur at a negotiable level, but a barn door for fodder, is placed at first floor level. A warehouse gantry girder could extend out of the mezzanine level floor opening to lift up goods from a cart or vehicle and bring it in.
An opening is a very universal architectural system. Openings are often mass produced with standard range of options. The openings follow a very strict exterior architectural regimen without consideration of the interior use related needs. For the above two reasons openings of same size, shape and design are used on all orientations, floor levels, neighbourhood conditions and geographic locations. Users wish to mark the openings’ system with individual personality, cultural ethos, beliefs, affinities etc. These occur as appendages, add-ons or treatments.
Openings with fixed glazing serve the function of a picture window framing a scenery -outward, or as a shop front windows to display items -inward looking. Fixed openings also become space dividers as partitions or cover element like a curtain wall.