Rooftop Greenscapes Offer A Way To Save Energy

One example of a decorative greenscape rooftop.

ROMULUS, MI — In a few years, it may be common to see gardens growing on top of urban buildings across the United States, providing relatively unusual greenery in the typical sea of concrete and blacktop. Many of these scenes are common in Europe and have been coming over to North America.

Greenscapes are popular for reasons that are obvious and not so obvious. First of all, the park-like atmosphere is aesthetically pleasing and provides a feeling of being in the country while living or working in the city. It may offer a tranquil respite for building occupants, stressed out from the daily grind of urban life.

For building owners and managers, the benefits also include energy savings resulting from having a mass of greenery growing on rooftops — savings that can add up to hundreds and thousands of dollars each year.

At a recent “Greenscapes on Rooftops Workshop,” sponsored by the Roof Consultants Institute (RCI) of Raleigh, NC, and held in Romulus, MI, a group of experts on greenscapes discussed the public and private benefits of green roof treatments and the various types of greenscapes that have been developed.

HEAT-REDUCTION BENEFITS

“Increased heat stress among building occupants creates a great number of health-related problems and also increases the need for air conditioning and refrigeration,” said Dr. Brad Bass, a member of Environment Canada’s Adaptation and Impact Research Group, located in the Institute for Environmental Studies at the University of Toronto, ON, Canada.

Bass listed the benefits of green technology, which for building owners are:

A means to reduce or eliminate other methods of dealing with storm water runoff;

A reduction in energy consumption;

Private green amenity or recreation space; and

A potential for producing high-value crops in urban settings.

For municipalities, Bass said the benefits include:

A reduction of summer temperatures;

Decreased frequency of severe smog episodes; and

Combined sewer overflow.

“It’s obvious that rooftops are heating up the cities and there is a greater need for urban forestry,” said Bass.

He explained that for every 1 degree of temperature increase, energy usage goes up 3% to 5%. A greenscape is designed to moderate heat fluctuations and overall temperature spikes.

“Take a Wal-Mart store in Atlanta [GA], for example,” Bass said. “It costs a lot to air condition a building of that size. Greenery could save up to 35% in energy costs for them.”

And it’s not just building owners who will reap energy savings. If enough urban buildings developed a greenscape strategy, the entire city environment could be a lot easier to live and work in. Not only are the gardens visually beautiful, stated Bass, they can noticeably lower outdoor temperatures.

“With a minimal amount of green roofs, daytime temperatures can be reduced by as much as three degrees,” Bass said.

MEASURABLE RESULTS

Jim Sheahan is the current chairman of the RCI Research Committee and president and founder of J.P. Sheahan Associates Inc., Midland, MI. He reported on findings from a greenscape research study.

Sheahan offered meeting attendees an example comparing a typical rooftop to a rooftop with a greenscape. (He prefers to use the word “garden.”)

He showed a temperature profile for a rooftop during a winter day with no snow on the roof. The garden rooftop maintained a constant temperature compared to a regular rooftop. With snow on the roof, the garden rooftop held temperatures constant, keeping the heat in. The regular rooftop showed more fluctuations.

“Heat gain and loss are more evident on a normal roof,” Sheahan said. “The heat flow differences on a snowless roof and hot roof in summertime show essentially no gain with a garden roof.”

In the summer, the same comparison showed a 120 degrees F fluctuation for the regular roof and a 40? fluctuation for the garden roof.

“Garden rooftops moderated heat flow into and out of the entire building, reducing energy demand on space conditioning,” Sheahan said. “The opposite is true for a regular roof because of the negative heat loss.”

Sheahan hopes studies like this will be used by building designers as well as building owners who are looking to reduce energy costs.

“Our first step is to make information available about our industry,” he said. “We would like details documented so that engineers can be assisted when designing systems for their buildings.”

For more information on the Roof Consultants Institute, call 919-859-0742 or visit www.rci-online.org (website).

Publication date: 09/16/2002

Looking for quick answers on air conditioning, heating and refrigeration topics? Try Ask ACHR NEWS, our new smart AI search tool. Ask ACHR NEWS