Curtain walling

Spandrel panels

A typical fully glazed curtain wall system will comprise a mixture of vision glass and opaque 'look-a-like' spandrel panels used to conceal the floor edge construction, ceiling void, heating plant, etc.

Spandrel panels pose specific difficulties since the dark colours used create high temperatures in the glass or the void behind it: 90°C is not unknown. Broadly, there are 2 methods of creating look-a-like effects:

  • adding an opacifier to the rear face of the glass; and
  • creating a dark painted void behind the glass - a shadow box.

Opacifiers are usually added to the fourth face of an IGU, being either a polyester or (mylar) film or alternatively a silicone spray treatment. Ceramic frits are also used. High temperatures can cause applied opacifier films to blister, while oil or latex paints are short lived as UV rays break down the molecular bond between the paint and the glass. Most opacifier failures are associated with shrinkage, weathering, oxidisation or adhesion failures in films that are sensitive to moisture, heat or light.

Annealed glass can be used for spandrel panels, but only if certain criteria are met. A ventilated void would be essential to remove warm air, and glass edges could also be polished to reduce the risk of thermal stress fractures.

If annealed glass were to fail, sharp shards of glass could fall out and so some form of scrim would need to be applied to the back face. Given the uncertainties of performance, heat strengthened or toughened glass is a more likely choice for spandrel panels. Heat strengthened glass can deal with higher working temperatures than annealed glass, although it can still shatter into shards. However, it does display less distortion due to roller wave.

Shadow box construction is difficult to achieve in practice and creates further problems of condensation control and heat build-up. High temperatures in the void behind the glass can permit volatile compounds to gas off and cause staining to the back of the glass when they condense. (Spandrel Panel Glazing, ATS-124, Pilkington Glass, 2005.)