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By Werner Lang and Thomas Herzog

Mind the gap

An important criteria for the classification of glass facades is the way in which they divide the gap between outer and inner layers. The gap may be undivided, or it may be partitioned by walls, glazing, wings, or other design techniques. This determines the functional characteristics of the facade, such as its heat and sound insulation, as well as the means of fire protection used within the structure.

Undivided facades are simple systems without structural elements between the inner and outer skins. This type poses some problems: Noise flows throughout the air space so that any rooms with open windows are invaded by sounds from the rooms above, below, or on either side. Fire and smoke can also spread freely through the gap.

THE WAY THE GLASS LAYERS ARE CONFIGURED DETERMINES HEAT AND SOUND INSULATION AND FIRE PROTECTION

In addition, air that accumulates at the top of the air space between the two layers is likely to get hot on sunny days. Openings in the outer skin at the top of the structure siphon out the warm air, while cooler replacement air is drawn from near the base of the building.

Undivided facades include the following:

Atria made by placing an additional layer of glass in front of or atop various wings of a building, creating a large, sheltered space. Atria are used for various purposes, such as meeting areas or cafeterias. Offices may open onto the atria, creating a more inviting and temperate work space. As in a conservatory or covered courtyard, the air temperature of these spaces is influenced by heat lost from the main building and by the weather conditions outside.

Atria reduce the thermal-performance demands on the walls that face inward. They can also collect solar radiation and lose heat from the surrounding building or buildings, keeping the temperatures within the space warmer, even on cold winter nights. Plants used in this space filter and moisten the air.

In the house-within-a-house, a secondary skin completely encloses a building or several buildings [see record, December 1999, page 78]. The solar radiation heats the air between the outer glazing and the facade of the building, thus reducing heat transmission and ventilation losses. Air can circulate in the whole space between the glazing and the original outer skin of the building, so parts of the interior not hit by the sun are heated. Summertime overheating is prevented by ventilation openings at the upper and lower extremes of the facade. The gap between the building and the glazing creates bonus space, which can be used for meeting areas, gardens, or other purposes.