Engineering buildings to perform
New Yorker John Hannum, a mechanical engineer, was surprised to see just how many glass towers have gone up in Toronto, on a recent visit to speak at the international Greenbuild conference in November.
"Driving into the city from the airport," says Hannum, "I'm driving by a bunch of highrise glass buildings... and I was somewhat surprised to see that in a colder climate, certainly."
Toronto’s condominium construction of the past ten years has rivaled that of New York City. According to Emporis.com, a website that tracks highrise towers around the world, Toronto was second only to New York in terms of the sheer number of condo highrise towers built, and first in terms of new condominiums per capita.
John Hannum is a polite American - and an engineer. He’s responsible for designing the heating and cooling systems that make it possible to live in a building made primarily out of glass.
"You can benefit from glass in commercial buildings," says Hannum, carefully choosing his words, so as not to be too harsh about Toronto’s wall of glass, "because glass in commercial buildings allows daylighting in. So glass can be very effective at offsetting energy loads."
But most of Toronto’s new glass towers are residential, and as John points out, glass is much less effective at offsetting the lighting load in residential buildings where most people are away during the day, only returning home at night.
Hannum is more than a polite visitor to Toronto. As a senior engineer with Israel Berg Associates, an international consulting firm which has worked on landmark buildings such as the Twin Towers and the Freedom Tower in New York City, Hannum was in Toronto to give a presentation called "Meeting the Market Demand for Glass."
But even if glass window walls are not the best choice for a residential building, Hannum is a realist about his role in serving the market demand for the look of glass.
"The reality is," says Hannum, "the market wants this stuff. So, rather than ignoring that, we need to embrace it and figure out solutions - triple-glazing the glass, or providing inter-layers within the glass surfaces so that you can improve the insulating value."
Little current incentive for high performance
Engineers are used to engineering their way out of seemingly impossible building designs. But walls built of glass present a unique challenge. With almost zero insulating value, every trick to build a better glass wall costs extra money. That too is reality - the average condo will not be one with the best window-wall money can buy.
Another reality - there's little incentive for developers to build high-performance walls. Neither the market - nor the Ontario building code - demands it. And the developers aren't the ones who'll pay the bills or the ongoing maintenance as the building ages.
"The perverse incentive for developers to build these buildings and not be accountable for the performance of them rears its head in many avenues," says Hannum. "If you're not paying attention to the detail of construction and design, it becomes a real problem."
Here in Toronto, Halsall Associates does engineering audits and reserve fund analysis to help condo boards assess the long-term renovations and ongoing maintenance that Toronto’s glass condo towers will need in the years ahead.
"At a fundamental level," says Doug Webber, leader of Halsall’s green team, as its Green Building Practice is known, "you can't build a poorer performing wall than a glass wall. But there are lots of things we do that aren’t good for us, like the cars we drive or the things we eat."
Webber and his colleague, Sally Thompson, have one of the most difficult juggling acts in town - advising condo boards on how much money to set aside for future repairs without making the cost of preparing for a rainy day so onerous that the building’s maintenance fees are too high compared with its peers.
But both Thompson and Webber acknowledge there are unique problems to living with glass, problems that go beyond the repair bills.
"We do get a lot of complaints," says Thompson, "particularly in the new condominiums, when we do the performance audit - the first-year warranty review - we get a lot of complaints of drafts at windows. People perceive the windows are leaking air, but the reality is it's just convection currents against the window. It's a lot of glass and so a lot of cold air falls off the glass and people perceive that as a draft".
Another issue - many of the glass window walls in Toronto’s new condominium stock will soon have problems with leakage.
Window wall systems require replacement
"So after 5 or so years," says Thompson, "we start having to seal up the joints in the window wall system." There are "quite a few" buildings, says Thompson, where Halsall engineers do major resealing projects after only five or six years.
And although the industry is making changes to improve the durability of those systems (Pro-Deminity, the Ontario Architecture Association’s mandatory insurance program for architects, requires window walls designed after January 2010 to include a rain screen to reduce leakage), Thompson says there are ongoing challenges that will add to the reserve fund contributions.
Solar panels are in place on a Rockefeller Center rooftop in midtown Manhattan.
Owners of all large buildings now
have to report energy usage.
(CP Photo/Mark Lennihan)
Over a period of 40 to 60 years, a window wall is much more expensive to maintain than other wall systems, mostly because the window wall system will require full replacement whereas other systems generally only require repair. Thompson notes that about 20% of the funds put into a reserve fund for a glass-walled building relate to the window wall - about three times as much as would be put aside related to windows in a building with insulated precast concrete or brick walls.
In January, the Ontario building code’s energy requirements will be strengthened, requiring developers to go 25 per cent beyond the Model National Energy Code, a standard set by the federal government. Some architects say that will likely lead to less window-wall construction in condominiums.
But Thompson and Webber agree that the building code, on its own, is not enough to produce higher-performing buildings – that real change will come as architects become more aware of building performance.
Engineering buildings to perform
"It’s about architecture redefining itself," says Thompson. "Is architecture the science of the look of the building? Or is architecture the science of the look AND the performance? Performance that goes beyond keeping water out, to the whole interaction of the systems – the comfort, the leakage resistance, the energy performance, and the facilitation of future, inevitable, maintenance."
But perhaps the most important change that can come to the residential highrise industry say all three engineers is mandatory energy labelling for buildings. In May of 2011, New York City has ordered owners of all large buildings to report annual energy usage - information that's compiled and shared. Also, every ten years, those buildings will perform an energy audit. While the city doesn't require building owners to complete any retrofits, it’s anticipated that by highlighting the data, the new rules will facilitate financing for retrofits and increase the likelihood that landlords will undertake those renovations.
Energy ratings, Thompson says, "drive disclosure for builders and awareness of purchasers, while also encouraging older buildings to upgrade – a win, win, win."