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Glazed Curtain Wall Terminology

By Stephen Kisielnicki, CCS

The American Architectural Manufacturers Association (AAMA) is the primary source for industry standards related to typical curtain wall types and components1. The following curtain wall elements and systems are outlined as described by AAMA.

Glazed curtain wall assemblies are a combined system of window lites within framing elements forming the building envelope.

Glass and glazing options
Standard float glass

  • Industry standard.
  • Typical thicknesses range from about 2.4-mm to 25 mm (3/32 in. to 1 in.)
  • Annealing used in conjunction with the float process eliminates stresses imposed
  • upon the glass during the manufacturing process, reducing breakage.

Tempered glass

  • Better impact resistances, increased bending strength for wind loads, and shatter control for life safety.
  • Shatters into very small pieces instead of large shards, providing a greater degree of safety for occupants.
  • Cutting, drilling, or edging required in the manufacturing process must be done prior to tempering, else the glass will shatter.
  • Exhibits some visual distortion.

Heat-strengthened glass

  • Strength between standard annealed float glass and tempered glass.
  • Good compromise when there is a possibility of breakage but life safety is not an issue.
  • Larger shards than tempered glass, though not as sharp as annealed glass.
  • Less distortion and less costly than tempered glass.

Laminated glass

  • Vinyl, polycarbonate, or cured resin interlayer bonded to one or more layers of glass to form a monolithic lite; interlayer holds the pieces together when the glass is broken and keeps the glass from shattering.
  • Effective solution for the many safety and security requirements becoming prevalent in architectural design.
  • Can be assembled in combination with any other type of glass to produce a very strong, secure lite.

Other glass considerations

Tinted and reflective glasses block portions of solar light transmittance, and are typically used to control the amount of light entering a building or for aesthetic reasons.

Spandrel glass is tinted, reflective-coated, or film-coated, and is typically used for aesthetic reasons in the fenestration. Solid insulated metal panels are often used in lieu of glass lites.

Insulating glass units (IGUs) are manufactured with a powdered gas or air-filled space between two or more panes of glass to provide energy efficiency.

Types of glazing

Glazing is the system or process used to support the glass in the frame and seal the dissimilar mating surfaces from the elements. There are several basic glazing options for curtain walls:

Wet glazing: preformed tape or gunnable (typically applied with a caulk gun) liquid sealant used to set the glass in the frame; versatile and adaptable to site conditions.

Dry glazing: manufactured compression gasket of rubber or vinyl used to support the glass; minimizes quality-control issues because it is pre-manufactured.

Structural glazing: in addition to sealing the assembly, the glazing material also carries a portion of the live and dead loads imposed on or by the glass.

  • Four sided: Sealant material utilized on four sides without the additional support of a frame on the exterior side of the glass. Has a "frameless" look.
  • Two sided: structural glazing sealant used on two sides, with traditionally glazed metal frame used on two sides.

Wet and dry glazing can be used effectively for factory, shop, or on-site glazing. Structural glazing is primarily accomplished once the glass is installed on-site.

Glazed curtain wall types and limitations

Glazed curtain walls are classified by how they are built, unlike punched opening windows which are classified by how they operate.

Stick system

  • First and most common curtain wall type developed by manufacturers.
  • Off-the-shelf components assembled on-site with individual mullions and rails to frame the vision and/or spandrel panels.

Unit panel system (unitized)

  • Pre-assembled, pre-glazed at the factory or shop, or glazed on-site and installed as panels of lites.

Unit mullion system

  • Compromise between the stick and unitized systems.
  • Pre-assembled units-pre-glazed or glazed on-site-are installed behind one- or two-story individual mullions.

Column cover and spandrel systems

  • Units can be pre- or site-assembled with infill vision glass and spandrel panels between the columns, and with column covers.
  • Units can be entirely pre-assembled or assembled on-site.

Notes
1 See AAMA MCWM-1,Metal Curtain Wall Manual.

Stephen Kisielnicki, CCS, is Associate and Senior Project Manager at the Baltimore, MD office of Gale Associates Inc., a consulting engineering firm specializing in building envelope technology.

 

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Originally published in May 2007

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