November 25, 2009

Green walls have been used to improve air quality and reduce noise in Santiago’s subway system.

Sustainable building

Green walls a growing trend in Santiago, Chile subway stations

SAUL CHERNOS

correspondent

Rush-hour commuters in Chile are breathing easy thanks to new green walls being installed in subway stations in the capital city of Santiago. Green walls are gaining popularity the world over.

The younger and perhaps more daring siblings of the more common green roofs are really not terribly different except that they’re often located indoors and have a vertical perspective.

Ignacio Espoz Babul, director of LatinGreen, a green wall installer in Santiago, described the benefits of platform-level gardens at Cities Alive!, the first annual congress of the World Green Roof Infrastructure Network, hosted last month by the City of Toronto and Green Roofs for Healthy Cities.

Living walls can help improve indoor air quality, fight noise pollution, and make for a pleasant commute for residents and visitors alike, Babul, an engineer by training, told delegates.

“Researchers in (South) Korea have concluded that pollution in the subway system is more severe than pollution from roadways,” he said.

“A study in London showed that dust in underground tunnels contains iron from the wheels and rail interface, quartz silica from brakes, and skin cells, hair cells and clothing fibre from passengers.”

Babul explained that studies show a significant reduction in indoor pollutants when plants are present.

In fact, he said, plants thrive on some of the more common pollutants found in underground subway systems, particularly carbon monoxide and carbon dioxide.

“These are perfect food for the plants,” Babul said.

Equally important for passengers, however, is that the plants absorb a significant amount of noise.

Particularly high-frequency sounds.

Subway users often complain about high noise levels emitted by subway trains, he said, explaining that noise measurements taken on platforms exceeded 100 decibels — enough to cause some hearing distress.

“Your daily ride on the subway can be hard on your nerves,” he said.

In a survey conducted earlier this year, Santiago riders reported increased happiness and energy levels.

They also noticed a more pleasant smell.

And, while subways can sometimes seem dark and dreary, such conditions are suitable for many species.

Underground temperatures in Chile typically range between 18C and 28C, which works well for many tropical plants.

Many species also fare well with relatively low levels of light.

With two test beds — 10 and 20 square metres respectively — successfully completed, plans are afoot to install a full-size living wall at Santa Ana Station, Babul said.

Toronto Transit Commission (TTC) chair Adam Giambrone, a city councillor, didn’t attend the conference, but said that he has toured several green walls and believes they can help clean the air and reduce noise.

However, he said the TTC is hesitant to build green walls at platform level for various reasons, including fire code restrictions.

“It’s a confined space down there,” Giambrone said, explaining there is little danger the plants themselves would catch fire, but they could produce smoke and the plastic materials used to embed them in the wall could also pose a potential danger from fumes if exposed to heat.

Maintenance is also an issue.

“People know how to scrub a cement wall, but TTC staff have been reluctant to figure out how to do maintenance on a green wall,” he said.

The TTC hasn’t completely shied away from greenery, however, unveiling a new green roof at Eglinton West station earlier this year.

“The commission did a cost-benefit analysis over 50 years and looked favourably at it because they were going to redo the roof anyway,” Giambrone said, adding that more green roofs are planned at stations where load-bearing walls are already in place.

He said if fire code and maintenance issues could be resolved, and the city had an outside partner willing to share the cost, living walls might become more feasible.

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