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The Engineer: Pull back the curtain – Common pitfalls in curtainwall installation

Specifiers and designers must be clear and provide acceptable torque ranges.

July 31, 2018  By David Heska

Every summer thousands of curtainwall projects are constructed across Canada. Regardless of the type of system installed, whether it’s stick or unitized, there can be some common issues that arise during and after construction.

First let’s briefly define the two major types of curtainwall systems.

Stick-built systems are installed and assembled together on a floor-by-floor, piece-by-piece basis (these pieces are the “sticks”). The benefits to this type of system are that it can be low-cost and more flexible in creating building shapes. Unfortunately, installation can be very labour-intensive and the quality of on-site workmanship is typically lower than factory-controlled workmanship. Unitized systems are pre-fabricated in modules and delivered to site in panels. Panels are typically one storey tall and connect like puzzle pieces. Because of this, unitized systems are constructed faster with a higher quality due to factory manufacturing, but the shipping costs increase.

Now let’s turn our attention to a few common issues, namely: torque, condensation, fire and IGU failure.


In curtainwall with pressure-plate glazing, one important element all parties involved need to know is the required torque pressures. Some specifications call for torque pressures as low as 20 inch-pounds. Others state “increase torque to 50 to 60 inch-pounds after all four sides have been secured.” Contractors recognize that over-torquing dramatically increases the likelihood of glass breakage and so they tend to err of the side of caution, however, if the torque pressure is not achieved water ingress may occur. Specifiers and designers must be clear and provide acceptable torque ranges. An on-site review should be completed to ensure that these design parameters are being met.

Another common deficiency is condensation on the interior surfaces of curtainwall elements. I’ve been involved on a few projects where the building owner has asked us to review “moisture problems” after only six months of occupancy. Typical issues causing condensation on interior surfaces are poor detailing, inadequate HVAC design and thermal bridging that has not been considered. As our industry moves forward, it is critical that design professionals and contractors work collaboratively to reduce these occurrences. Education is also important so that words and drawings on a page can be translated into facades that can actually be built in the real world.

An increased awareness of fire safety is also leading to more attention to proper smoke-sealing between the floor slab edge and the back of the curtainwall assemblies. Compartmentalization of areas from one another is important to slow down the passage of fire between floors. Typical details show fire-rated assemblies that have been approved to Canadian standards are required to provide confidence that the materials will remain in place during a fire event. Often, there is a need for clarity around site-specific conditions where the “typical” detail does not apply.

Finally, an issue that is becoming more popular as our building stock gets older is IGU replacement in curtainwall. Around the 25-year mark, some of the seals on insulating glass units begin to fail and building owners are faced with a decision to either reactively replace fogged units (sometimes at a rate of 10 to 20 IGUs per year) or proactively upgrade their curtainwall system. The payback for 100 per cent IGU replacement can be compelling in most cases due to substantial savings resulting from advanced IGU technology today (i.e. better solar heat gain coefficients and overall U-values).

So if you’re visiting downtown Vancouver, Calgary, Toronto or Montreal this summer, take a look up at some of the curtainwall buildings and ask yourself, “What could have been done by the engineer or the contractor or the manufacturer to make this a better building”?

David Heska, P.Eng. is a director with WSP’s building sciences team in southwestern Ontario. He oversees the operation of the Hamilton, Kitchener and Windsor offices. David has been involved on window simulation projects as well as the design and replacement of windows in commercial and residential buildings. He can be reached at

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