Comment: a tower rises from the ashes

Seen from New Jersey, the new World Trade Center tower stands out clearly on the Manhattan skyline. Tall and slender, it appears twice as tall as the other skyscrapers.

I was mindful of the events of September 11, 2001 while visiting New York for the ASHRAE Winter Conference. So I took the group tour of the WTC site and 9/11 Memorial. Located on what was “Ground Zero,” the memorial consists of two low black granite square pools laid over the footprints of the original WTC 1 and 2. At the centre of each pool the water simply falls down into what looks like a bottomless void. It seems a bleak artistic statement, but while I was there the wind whipped the water up high into amazing dancing sprays. (The church near the site that was used as a resting spot by the rescue workers has become a more personalized shrine, with photographs and artifacts on display.)

Near to the black pools the new tower rises sleek and beautiful with its chamfered glass walls and spire reaching to 1,776 feet (541-m), symbolic of the American Declaration of Independence. It is no longer called the “Freedom Tower,” but has become the commercialized “One World Trade Center.”

For people in the construction industry it’s still difficult to think that buildings were the means by which the terrorists were able to wreak so much havoc. The events that unfolded that day represented such a reversal of what buildings are supposed to be — shelters from the storm and other dangers.

Yet around the world 9/11 has not stunted the drive to develop taller and taller towers. The Council for Tall Buildings and Urban Habitat graphs show a steep rise in buildings over 200 metres high. Before 1996 only a handful were being built every year, but aside from a short dip in 2002 the number rises sharply, to 70 completed in 2010, and 81 in 2011. The majority (74%) of these recent developments are in Asia.

Urban designers generally favour tall buildings because they add density, thus reducing sprawl. But are skyscrapers environmentally always the way to go? Manhattan is dense, with plenty of highrises, but traffic creeps along by inches. People might not be using their own cars, but they still need “stuff,” and delivery vans, buses, taxis and pedestrians clog every intersection.

I’ve not been able to study any research on the energy use intensity of towers compared to low-rise structures, but I’d guess that the glass walls, along with elevators and other power-drawing infrastructure that’s necessary in vertical dwellings, offset many of the energy savings gained by living contiguously.

At the ASHRAE conference John Kontokosta of the NYU CUSP centre presented data on New York’s commercial building stock that many designers will find disturbing (“Surprising Disclosures,” p. 41). One of their findings was that the city’s older buildings are more energy efficient than those from the last 20 years. A reason, they felt, was that despite today’s focus on energy efficient designs, the extra amenities and luxury features in today’s towers add to the overall loads. Besides individual building research (CIRS, p. 18), more studies like CUSP’s that look at the big urban picture will be helpful for directing sustainable design in the future.Bronwen Parsons