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Options to consider behind the curtain wall

Dan O'Reilly
Options to consider behind the curtain wall

With so much new condominium and office tower construction underway in Toronto, it might be easy to overlook the fact the city has a large inventory of older commercial buildings that need some restorative care.

That was the focus of a Construct Canada seminar on the best method practices for retrofitting the facades of occupied commercial buildings.

"Many buildings from the 1960s, 1970s and even the 1980s are due for a retrofit," said Rob Wood, president of C3 Polymeric, a Brampton, Ont.-based firm that specializes in curtain wall retrofits.

Curtain walls are the "outer skin" of buildings and their purpose includes regulating the interior environment, resisting wind loads and other external forces as well as being an architectural feature.

"They have been the dominant (building) facade covering for the past 30 years," said Wood, explaining curtain walls are "not what holds the building up. But you don’t want them to fall down."

They do fail for reasons that include the design and/or construction details and the finite lifespan of the components.

"At some point everything gets old," he said. Although the design might have been detailed incorrectly, "the best practices of the ’60s and ’70s might not be the best practices now."

Some of the symptoms of curtain wall deterioration include water penetration, air penetration or air leakage, or fogging of the insulated glazing units. The most extreme example would be falling glass, said Wood, who showed a slide of a car that had been damaged when that occurred.

A number of questions need to be asked when a curtain wall fails.

"What was the cause? What was done right and what was wrong (in the design)?" he said.

Once a decision has been made that a retrofit is required, there are many factors that determine the best methods. The main approaches include refurbishing, overcladding, or recladding, which is a full removal of the old cladding and replacing it with a new one.

All three methods have pros and cons and pose significant challenges.

"There’s the potential for extreme disruption to the tenants," explained Wood.

There is less impact to tenants with a refurbishment. Other advantages include construction speed and a relatively inexpensive price tag when compared to the other procedures. This model, however, has the least amount of architectural flexibility and the potential for thermal upgrades is limited.

Overcladding is the installation of new cladding over the existing one. It can be customized and, in some cases, may be the only technically feasible option. But there is a technical risk, said Wood, explaining its success relies on the structural integrity of the original system.

An example of an overcladding project is the Crown (formerly Zurich) building in Toronto, a 25-floor tower constructed in 1969 with a unitized curtain system comprised of single interior glazed vision units.

"The existing window system was exhibiting significant technical problems, including water penetration and heat loss/gain through the single glazing," described Wood.

A new curtain wall system designed and installed by C3 Polymeric was installed from the exterior over the original window system. Once the new curtain wall was in place, the original vision glass was removed and both the original and new frames were clad from the interior, he said.

During his seminar, the audience was provided with highlights of the intensive investigation and design C3 Polymeric had to conduct in preparation for that project.

Some of that pre-construction analysis included erecting an onsite mock up, thermal analysis and lab testing of the new components.

"We can take the principles, but not the system," said Wood, explaining that although the curtain wall was specifically designed for the Crown building, the techniques could be applied to other projects.

As for recladding, it is the most expensive retrofit alternative, with costs that can exceed $200 per square foot. But it does provide maximum architectural flexibility and the best thermal options, said Wood.

Whatever method building owners and their consultants choose, a successful curtain wall retrofit depends on thorough planning before a project commences and an equally thorough inspection and monitoring during the construction, Wood emphasized.

"Don’t stop investigating and looking," he said.

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