The Best Laid Plans: Risk management in building envelope design and construction

Decorative screens in front of the curtain wall can pose maintenance challenges if not considered during design.

Esthetics of glass
Another consideration when specifying glass for the building envelope is esthetics. While maintaining a desired appearance may not be as critical to material performance as managing breakage, it is nonetheless important to a building’s overall look and style. With multiple options available to designers through glass tints, films, coatings, and frit combinations, it is prudent to construct a physical glass mockup to better gauge the desired appearance.

Designers should also make careful and informed decisions about the materials that will be adjacent to, and on, the glass. Poorly chosen materials can cause unwanted and premature changes in the appearance of the glass, including coating corrosion, film peeling, and/or moiré effect from overlapping frit patterns.

Glass often fulfils occupants’ and designer’s desire to connect with the exterior environment. However, this intended connection is often thwarted when occupants pull blinds and curtains closed to reduce glare or prevent overheating. While there have been technological advances with low-emissivity (low-e) coatings and shading devices, their effectiveness does have a limit and cannot compete with an opaque wall with respect to thermal performance and heat control. Rather than designing with a focus on quantity of glass, designers should focus on the quality and location of the visual connection between interior and exterior. For example, there is little need for glass at floor level in a space filled with office desks.

It is also important to understand the surrounding environmental conditions. The sun’s rays reflecting off a glass façade can alter the desired appearance of the building and can also affect the surrounding environment. Highly reflective surfaces can reflect heat to neighbouring buildings and public spaces, increasing their cooling loads and making conditions less comfortable for occupants.

Designers need to ask questions
As the use of glass increases, designers need to consider a host of questions throughout the entire design and evaluation process, including:

  • How will the glass be supported?
  • What is the expected load distribution?
  • What are the requirements for movement accommodation?
  • What is the desired post-breakage behaviour and will this be achieved with this design?
  • What thermal performance requirements or considerations should be made?
  • How will the glass be maintained (i.e. cleaned/repaired)?
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