Undivided facades allow air to flow freely within the space between the inner and outer skins. They are simple and inexpensive to build. This type presents several problems, but most importantly, noise, smoke, fire, and odors can move, unimpeded, from one space into another. Also, warm air accumulates at the top of the air space, while cool air pools at the bottom. Unless there are openings at the top of the facade to vent that hot air, the upper floors of the building will be hot on sunny days.
Natural ventilation is best in shaft-type facades.
These work by allowing fresh air to enter the building through openings in the outer skin between the shafts. A double-window effect, similar to solar chimneys, allows cooler air to enter at the lower portion of the shaft while warmer exhaust air leaves through the upper part of the window. In other words, the temperature differences induce an upward flow of air in the shaft, improving air movement within the building. Air is supplied by an HVAC system and natural ventilation is not possible. Warm air exhausted from the building as well as solar gain warm the air in the gap, or corridor, reducing the amount of heat lost through the facade during cold weather and improving comfort.