April 27, 2007

Dual Skin

Designs not popular in Canada's harsh climates

DAN O’REILLY

correspondent

The University of Toronto’s Terrence Donnelly Centre for Cellular and Biomolecular Research is among those buildings designed with a dual skin.

The technology is not often used in Canada, partly because of the country’s harsh climate.

Like a lawyer carefully delivering all the facts, a University of Waterloo architectural professor outlined the pros and cons of the dual skin wall system for the benefit of the building envelope industry recently.

STANTEC/WILLIAM CONWAY

U of T's Terrence Donnelly Centre for Cellular and Biomolecular Research with its elaborate curtain wall and entranceway is among buildings with a dual skin. It was designed by Behnisch, Behnisch and achitectsAlliance.

Double skin walls are being used on several vanguard building, such as the University of Toronto’s Centre for Cellular and Biomolecular Research,Terry Boake told those attending a recent Building Envelope Solutions seminar in Toronto.

The dual skin facade system is essentially a pair of glass skins separated by an air corridor.

The main layer is somewhat similar to a curtain wall and is usually insulating. But unlike a curtain wall, there is an extra layer of glass, with an air space between the two layers that acts as insulating barrier against temperature extremes, noise and wind, she explained.

While there are number of double skin wall buildings in Europe, they’re not very common in North America, and especially in Canada, for reasons that include harsh climate.

“One of the largest concerns in cold climates is the potential for condensation in the air space and on elements and surfaces within that space.”

Another inhibiting factor is the lack of adequately trained people to build them, she said.

“In Canada and the United States, the number of contractors who can put them together are few and far between. Anybody can put them together in an office.”

There’s still a lot to be learned about dual wall systems as detailed information about cost and ultimate performance is not readily available, Boake said.

Drawing upon her own research and studies by trade journals, she says there are four basic types of double skin systems as defined by an article in the Architectural Record – buffer facade, extract-air facade, twin facade and the hybrid facade.

Dating back almost a century, buffer facades were invented to maintain daylight in buildings while increasing sound properties of the wall system.

It uses two layers of single glazing, spaced 250 to 900 mm apart, sealed and allowing fresh air into the building through a control means, such as a separate HVAC system or box windows.

A modern example of this type is the Occidental Chemical/Hooker Building in Niagara Falls, New York, said Boake.

The extract-air facade is a single layer of glazing placed on the interior of a main facade of double glazing. The air space between those two layers becomes part of the HVAC System, with the heated used air extracted through the cavity with the use of fans, tempering the inner layer while the outer layer of insulating glass minimizes heat-transmission lost. With a conventional curtain wall or thermal wall glass system inside a single glazed building skin and an outer glazing of either laminated or insulating glass, the twin-facade is probably the most common because it allows for natural ventilation through openings in the skin.

“Normally, there has to be an interior space of at least 500 to 600 mm to permit cleaning.”

Designed by Italian architect Renzo Piano, the Tjibaou Cultural Center in New Caledonia is an example of a hybrid facade, which combines one or more of the basic characteristics of the other three facades to create a new system, said Boake.

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