Architecture Notes

The fundamental definition of the term curtain wall is an exterior wall that is not load bearing, acting solely as a skin to shield from the elements.  The introduction of structural frames facilitated the development of these facades.  Today, we most commonly associate curtain wall with glass exterior walls that provide significant natural light to the building’s interior.  There is a tremendous amount of technical information to understand about the design of curtain walls, but here are a few basic notes.

Stick vs. Unitized

These terms refer to assembly methods.

In a stick system, the glass and surrounding mullions are installed one piece at a time.  The stick system is economical due to lower transportation costs and the ability to work on different areas of the building at the same time.  The stick system requires glazing on-site, potentially reducing the quality control of the glazing installation.  The stick system is best for small projects.

Unitized systems are fabricated into larger units in the factory that interlock together on site.  The industry as a whole has moved toward the use of more unitized systems.  The advantage is fabrication in a controlled factory environment.  In general, the more components assembled in controlled conditions, the more reliable the performance.

Glass Types

Check out the previous post on various types of glass.

Insulating units are commonly used for their thermal resistance.  These consist of 2 or more lites held apart by a spacer.  The spacer contains a desiccant to keep the air space free of visible moisture.  A double seal around the unit insures the space is hermetically sealed.

Coatings on the glass surfaces affect the reflection, absorption and radiation of solar energy.  Solar reflective and low emissivity (low-E) coatings are most common.  Such coatings may be added to the no.2 or 3  surface of an insulated unit – see diagram below.  Glass selections and coatings should be carefully designed in conjunction with the building’s mechanical ventilation system to properly anticipate energy loads.

Other Glass Criteria to Consider

• Thermal and mechanical stresses in the glass
• Glass deflection and wind load
• Bow, warp and distortion

Resources

Check out the more comprehensive information available in these sources.  Please share additional links in the comments.

• National Institute of Building Sciences – Whole Building Design Guide
• Designing the Exterior Wall by Linda Brock