The relative position of glass and structure
The structure can be positioned relative to the glazing in variety of ways.
In most atria the glass forms the external skin, conventionally supported on the structure immediately below. The structure is therefore fully exposed to internal view. However, alternative arrangements are possible, either placing the structure external to the glass, or concealing it behind a laylight.
The structure can be placed external to the glass.
Structure can be placed external to the glass surface, the most significant example being Lloyds of London where both roof and vertical side walls are carried on space trusses giving a weightless effect internally.
A laylight is an inner skin of glazing concealing the structure and diffusing light.
It was common practice in the l9th century to use two skins of glazing fixed externally and internally to industrial trusses. The inner glazing or 'laylight' concealed the structure and formed a light diffuser to the interior. Such designs often produced dramatic interiors, like Otto Wagner's Austrian Postal Savings Bank, Vienna (l904-6), or the opportunity for employing stained 'art glass' as ceiling decoration, an outstanding example being the domed space of Galeries Lafayette, the Paris department store.
A few modern examples exist, the most elegant being the glasscrete vault inserted in a banking hall in Prague by Oldrick Tyl in l930, and Frank Lloyd Wright reverted to the Lafayette concept with the decorative laylight devised for the Guggenheim Museum in l956.
