'Glass box' architecture leads to lower thermal performance, higher costs, expert says

Efforts to achieve carbon-neutrality in a couple of decades, as is the goal of Architecture 2030, are unrealistic if developers continue to build ‘glass box’ structures.

Designers wanting to reduce the environmental footprint of their buildings are in fact often adding to the environmental load by overglazing their structures, a Toronto architect says.

Many designers are upping the amount of glass in their facades in order to increase daylighting and provide good views, explained Jenny McMinn of Halsall Associates. But, she warned, there’s a significant downside in increased energy costs associated with lost heating and cooling.

“One would think our architecture is becoming more aggressive and performing better, but in fact it’s quite the reverse,” McMinn said. “We were actually doing quite well with some basic technology, but with the advent of glass and steel and taller and taller buildings we were romanticized by adding more glass and showing more transparency, and the thermal performance is ridiculous.”

McMinn offers examples such as the Shard London Bridge Tower, the Pearl Tower in Guangzhou China, the Burj Dubai, and the Bank of America in New York City, as highly-glazed and yet environmentally-friendly buildings. McMinn said designers are glazing aggressively and then compensating for lost heating and cooling by adding costly mechanical systems such as radiant panels, external shading devices with timers, and costly high-performance glazing.

“Developers are looking to build a global icon and not really considering the region within which they’re building,” McMinn said.

Citing figures drawn from the web site Emporis.com, McMinn said the Bank of America included an efficient, high-tech mechanical system to support its high degree of glazing, but this came with a five per cent cost premium.

In contrast, the building envelope of the Banner Bank Building in Boise, Idaho is 55 per cent glass and had a cost premium of zero.

“Effectively you are improving the thermal comfort but adding energy and layers of material onto a problem that could be solved a lot more simply,” McMinn said.

“There’s a line in between the two where we need to be pushing our designs.”

McMinn added that efforts to reduce fossil fuel consumption to zero in order to achieve carbon-neutrality a couple of decades from now, as groups such as Architecture 2030 are urging North American municipalities to do, are unrealistic if developers continue to build “glass-box” structures.

Describing Toronto as a heating dominated city that also has cooling requirements, McMinn said daylighting does reduce a building’s energy load, but excessive glass is otherwise costly. She urged designers to find a “sweet spot” that improves the comfort level for building occupants in an economic and environmentally-friendly fashion. “Cooling drives capital costs up, and heating drives energy costs. The thermal performance of buildings is critical in our climate.”

Rating and certification systems appear to be catching on. LEED for Existing Buildings, for instance, includes Energy Star as a means of comparing similar buildings. In Tokyo, McMinn said, condominium developers are legally required to demonstrate their energy performance. “Toronto developers should be considering energy labelling as a means of remaining competitive as industry leaders.”